[PATCHSET v7] io_uring IO interface

[PATCHSET v7] io_uring IO interface

[Jens Axboe]

Here's v7 of the io_uring interface. Not a lot of changes this time
around, mostly corner cases and error handling that hadn't been
exercised yet.

Only new "feature" is an improvement in sequential buffered IO
performance. This is done by piggy backing on to existing async work if
we're sequential to the previous work item, and it hasn't finished yet.
This greatly reduces the overhead, context switches, and increases the
performance a lot. Using io_uring-cp, as test program that does cp with
io_uring, I saw a 5x improvement in speed when copying a large file.
It's now faster than plan 'cp.

The x86/x86-64 system calls were renumbered, so if you are testing,
be sure to pull apply the renumbering. The fio and liburing repos have
been updated.

The liburing git repo now has a man page for io_uring_register(2),
thanks to Jeff Moyer. Outside of that, not much activity there since
last time. Clone the liburing repo here:

git://git.kernel.dk/liburing

Patches are against 5.0-rc3, and can also be found in my io_uring branch
here:

git://git.kernel.dk/linux-block io_uring

Changes since v6:
- Fix leak of iovec in write path for larger writes
- Fix CQ event filling for error handling of workqueue buffered items
- Improve sequential buffered IO performance
- Fix leak of accounted mem in error path for io_uring_create() (Roman)
- Rebase on v5.0-rc3
- Check for entries == 0 in io_uring_create (Jeff)
- Renumber system calls so they are ready for Arnds unification

 Documentation/filesystems/vfs.txt      |    3 +
 arch/x86/entry/syscalls/syscall_32.tbl |    3 +
 arch/x86/entry/syscalls/syscall_64.tbl |    3 +
 block/bio.c                            |   59 +-
 fs/Makefile                            |    1 +
 fs/block_dev.c                         |   19 +-
 fs/file.c                              |   15 +-
 fs/file_table.c                        |    9 +-
 fs/gfs2/file.c                         |    2 +
 fs/io_uring.c                          | 2540 ++++++++++++++++++++++++
 fs/iomap.c                             |   48 +-
 fs/xfs/xfs_file.c                      |    1 +
 include/linux/bio.h                    |   14 +
 include/linux/blk_types.h              |    1 +
 include/linux/file.h                   |    2 +
 include/linux/fs.h                     |    6 +-
 include/linux/iomap.h                  |    1 +
 include/linux/sched/user.h             |    2 +-
 include/linux/syscalls.h               |    7 +
 include/uapi/asm-generic/unistd.h      |    8 +-
 include/uapi/linux/io_uring.h          |  141 ++
 init/Kconfig                           |    9 +
 kernel/sys_ni.c                        |    4 +
 23 files changed, 2857 insertions(+), 41 deletions(-)

-- 
Jens Axboe

[PATCH 01/18] fs: add an iopoll method to struct file_operations

[Jens Axboe]

From: Christoph Hellwig <hch@lst.de>

This new methods is used to explicitly poll for I/O completion for an
iocb.  It must be called for any iocb submitted asynchronously (that
is with a non-null ki_complete) which has the IOCB_HIPRI flag set.

The method is assisted by a new ki_cookie field in struct iocb to store
the polling cookie.

TODO: we can probably union ki_cookie with the existing hint and I/O
priority fields to avoid struct kiocb growth.

Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 Documentation/filesystems/vfs.txt | 3 +++
 include/linux/fs.h                | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index 8dc8e9c2913f..761c6fd24a53 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -857,6 +857,7 @@ struct file_operations {
 	ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
 	ssize_t (*read_iter) (struct kiocb *, struct iov_iter *);
 	ssize_t (*write_iter) (struct kiocb *, struct iov_iter *);
+	int (*iopoll)(struct kiocb *kiocb, bool spin);
 	int (*iterate) (struct file *, struct dir_context *);
 	int (*iterate_shared) (struct file *, struct dir_context *);
 	__poll_t (*poll) (struct file *, struct poll_table_struct *);
@@ -902,6 +903,8 @@ otherwise noted.
 
   write_iter: possibly asynchronous write with iov_iter as source
 
+  iopoll: called when aio wants to poll for completions on HIPRI iocbs
+
   iterate: called when the VFS needs to read the directory contents
 
   iterate_shared: called when the VFS needs to read the directory contents
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 811c77743dad..ccb0b7a63aa5 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -310,6 +310,7 @@ struct kiocb {
 	int			ki_flags;
 	u16			ki_hint;
 	u16			ki_ioprio; /* See linux/ioprio.h */
+	unsigned int		ki_cookie; /* for ->iopoll */
 } __randomize_layout;
 
 static inline bool is_sync_kiocb(struct kiocb *kiocb)
@@ -1786,6 +1787,7 @@ struct file_operations {
 	ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
 	ssize_t (*read_iter) (struct kiocb *, struct iov_iter *);
 	ssize_t (*write_iter) (struct kiocb *, struct iov_iter *);
+	int (*iopoll)(struct kiocb *kiocb, bool spin);
 	int (*iterate) (struct file *, struct dir_context *);
 	int (*iterate_shared) (struct file *, struct dir_context *);
 	__poll_t (*poll) (struct file *, struct poll_table_struct *);
-- 
2.17.1

Re: [PATCH 01/18] fs: add an iopoll method to struct file_operations

[Christoph Hellwig]

On Wed, Jan 23, 2019 at 08:35:12AM -0700, Jens Axboe wrote:
> TODO: we can probably union ki_cookie with the existing hint and I/O
> priority fields to avoid struct kiocb growth.

Please kill this comment.  While this should be doable the semantics
would be a bit nasty, so unless we have to I'd rather skip this work
for now.

Re: [PATCH 01/18] fs: add an iopoll method to struct file_operations

[Jens Axboe]

On 1/28/19 7:25 AM, Christoph Hellwig wrote:
> On Wed, Jan 23, 2019 at 08:35:12AM -0700, Jens Axboe wrote:
>> TODO: we can probably union ki_cookie with the existing hint and I/O
>> priority fields to avoid struct kiocb growth.
> 
> Please kill this comment.  While this should be doable the semantics
> would be a bit nasty, so unless we have to I'd rather skip this work
> for now.

Agree, killed.

-- 
Jens Axboe

[PATCH 02/18] block: wire up block device iopoll method

[Jens Axboe]

From: Christoph Hellwig <hch@lst.de>

Just call blk_poll on the iocb cookie, we can derive the block device
from the inode trivially.

Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/block_dev.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 58a4c1217fa8..f18d076a2596 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -293,6 +293,14 @@ struct blkdev_dio {
 
 static struct bio_set blkdev_dio_pool;
 
+static int blkdev_iopoll(struct kiocb *kiocb, bool wait)
+{
+	struct block_device *bdev = I_BDEV(kiocb->ki_filp->f_mapping->host);
+	struct request_queue *q = bdev_get_queue(bdev);
+
+	return blk_poll(q, READ_ONCE(kiocb->ki_cookie), wait);
+}
+
 static void blkdev_bio_end_io(struct bio *bio)
 {
 	struct blkdev_dio *dio = bio->bi_private;
@@ -410,6 +418,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
 				bio->bi_opf |= REQ_HIPRI;
 
 			qc = submit_bio(bio);
+			WRITE_ONCE(iocb->ki_cookie, qc);
 			break;
 		}
 
@@ -2076,6 +2085,7 @@ const struct file_operations def_blk_fops = {
 	.llseek		= block_llseek,
 	.read_iter	= blkdev_read_iter,
 	.write_iter	= blkdev_write_iter,
+	.iopoll		= blkdev_iopoll,
 	.mmap		= generic_file_mmap,
 	.fsync		= blkdev_fsync,
 	.unlocked_ioctl	= block_ioctl,
-- 
2.17.1

[PATCH 03/18] block: add bio_set_polled() helper

[Jens Axboe]

For the upcoming async polled IO, we can't sleep allocating requests.
If we do, then we introduce a deadlock where the submitter already
has async polled IO in-flight, but can't wait for them to complete
since polled requests must be active found and reaped.

Utilize the helper in the blockdev DIRECT_IO code.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/block_dev.c      |  4 ++--
 include/linux/bio.h | 14 ++++++++++++++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index f18d076a2596..392e2bfb636f 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -247,7 +247,7 @@ __blkdev_direct_IO_simple(struct kiocb *iocb, struct iov_iter *iter,
 		task_io_account_write(ret);
 	}
 	if (iocb->ki_flags & IOCB_HIPRI)
-		bio.bi_opf |= REQ_HIPRI;
+		bio_set_polled(&bio, iocb);
 
 	qc = submit_bio(&bio);
 	for (;;) {
@@ -415,7 +415,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
 		nr_pages = iov_iter_npages(iter, BIO_MAX_PAGES);
 		if (!nr_pages) {
 			if (iocb->ki_flags & IOCB_HIPRI)
-				bio->bi_opf |= REQ_HIPRI;
+				bio_set_polled(bio, iocb);
 
 			qc = submit_bio(bio);
 			WRITE_ONCE(iocb->ki_cookie, qc);
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 7380b094dcca..f6f0a2b3cbc8 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -823,5 +823,19 @@ static inline int bio_integrity_add_page(struct bio *bio, struct page *page,
 
 #endif /* CONFIG_BLK_DEV_INTEGRITY */
 
+/*
+ * Mark a bio as polled. Note that for async polled IO, the caller must
+ * expect -EWOULDBLOCK if we cannot allocate a request (or other resources).
+ * We cannot block waiting for requests on polled IO, as those completions
+ * must be found by the caller. This is different than IRQ driven IO, where
+ * it's safe to wait for IO to complete.
+ */
+static inline void bio_set_polled(struct bio *bio, struct kiocb *kiocb)
+{
+	bio->bi_opf |= REQ_HIPRI;
+	if (!is_sync_kiocb(kiocb))
+		bio->bi_opf |= REQ_NOWAIT;
+}
+
 #endif /* CONFIG_BLOCK */
 #endif /* __LINUX_BIO_H */
-- 
2.17.1

Re: [PATCH 03/18] block: add bio_set_polled() helper

[Christoph Hellwig]

On Wed, Jan 23, 2019 at 08:35:14AM -0700, Jens Axboe wrote:
> For the upcoming async polled IO, we can't sleep allocating requests.
> If we do, then we introduce a deadlock where the submitter already
> has async polled IO in-flight, but can't wait for them to complete
> since polled requests must be active found and reaped.
> 
> Utilize the helper in the blockdev DIRECT_IO code.
> 
> Signed-off-by: Jens Axboe <axboe@kernel.dk>

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>

[PATCH 04/18] iomap: wire up the iopoll method

[Jens Axboe]

From: Christoph Hellwig <hch@lst.de>

Store the request queue the last bio was submitted to in the iocb
private data in addition to the cookie so that we find the right block
device.  Also refactor the common direct I/O bio submission code into a
nice little helper.

Signed-off-by: Christoph Hellwig <hch@lst.de>

Modified to use bio_set_polled().

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/gfs2/file.c        |  2 ++
 fs/iomap.c            | 43 ++++++++++++++++++++++++++++---------------
 fs/xfs/xfs_file.c     |  1 +
 include/linux/iomap.h |  1 +
 4 files changed, 32 insertions(+), 15 deletions(-)

diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c
index a2dea5bc0427..58a768e59712 100644
--- a/fs/gfs2/file.c
+++ b/fs/gfs2/file.c
@@ -1280,6 +1280,7 @@ const struct file_operations gfs2_file_fops = {
 	.llseek		= gfs2_llseek,
 	.read_iter	= gfs2_file_read_iter,
 	.write_iter	= gfs2_file_write_iter,
+	.iopoll		= iomap_dio_iopoll,
 	.unlocked_ioctl	= gfs2_ioctl,
 	.mmap		= gfs2_mmap,
 	.open		= gfs2_open,
@@ -1310,6 +1311,7 @@ const struct file_operations gfs2_file_fops_nolock = {
 	.llseek		= gfs2_llseek,
 	.read_iter	= gfs2_file_read_iter,
 	.write_iter	= gfs2_file_write_iter,
+	.iopoll		= iomap_dio_iopoll,
 	.unlocked_ioctl	= gfs2_ioctl,
 	.mmap		= gfs2_mmap,
 	.open		= gfs2_open,
diff --git a/fs/iomap.c b/fs/iomap.c
index a3088fae567b..4ee50b76b4a1 100644
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -1454,6 +1454,28 @@ struct iomap_dio {
 	};
 };
 
+int iomap_dio_iopoll(struct kiocb *kiocb, bool spin)
+{
+	struct request_queue *q = READ_ONCE(kiocb->private);
+
+	if (!q)
+		return 0;
+	return blk_poll(q, READ_ONCE(kiocb->ki_cookie), spin);
+}
+EXPORT_SYMBOL_GPL(iomap_dio_iopoll);
+
+static void iomap_dio_submit_bio(struct iomap_dio *dio, struct iomap *iomap,
+		struct bio *bio)
+{
+	atomic_inc(&dio->ref);
+
+	if (dio->iocb->ki_flags & IOCB_HIPRI)
+		bio_set_polled(bio, dio->iocb);
+
+	dio->submit.last_queue = bdev_get_queue(iomap->bdev);
+	dio->submit.cookie = submit_bio(bio);
+}
+
 static ssize_t iomap_dio_complete(struct iomap_dio *dio)
 {
 	struct kiocb *iocb = dio->iocb;
@@ -1566,7 +1588,7 @@ static void iomap_dio_bio_end_io(struct bio *bio)
 	}
 }
 
-static blk_qc_t
+static void
 iomap_dio_zero(struct iomap_dio *dio, struct iomap *iomap, loff_t pos,
 		unsigned len)
 {
@@ -1580,15 +1602,10 @@ iomap_dio_zero(struct iomap_dio *dio, struct iomap *iomap, loff_t pos,
 	bio->bi_private = dio;
 	bio->bi_end_io = iomap_dio_bio_end_io;
 
-	if (dio->iocb->ki_flags & IOCB_HIPRI)
-		flags |= REQ_HIPRI;
-
 	get_page(page);
 	__bio_add_page(bio, page, len, 0);
 	bio_set_op_attrs(bio, REQ_OP_WRITE, flags);
-
-	atomic_inc(&dio->ref);
-	return submit_bio(bio);
+	iomap_dio_submit_bio(dio, iomap, bio);
 }
 
 static loff_t
@@ -1691,9 +1708,6 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
 				bio_set_pages_dirty(bio);
 		}
 
-		if (dio->iocb->ki_flags & IOCB_HIPRI)
-			bio->bi_opf |= REQ_HIPRI;
-
 		iov_iter_advance(dio->submit.iter, n);
 
 		dio->size += n;
@@ -1701,11 +1715,7 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
 		copied += n;
 
 		nr_pages = iov_iter_npages(&iter, BIO_MAX_PAGES);
-
-		atomic_inc(&dio->ref);
-
-		dio->submit.last_queue = bdev_get_queue(iomap->bdev);
-		dio->submit.cookie = submit_bio(bio);
+		iomap_dio_submit_bio(dio, iomap, bio);
 	} while (nr_pages);
 
 	/*
@@ -1916,6 +1926,9 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 	if (dio->flags & IOMAP_DIO_WRITE_FUA)
 		dio->flags &= ~IOMAP_DIO_NEED_SYNC;
 
+	WRITE_ONCE(iocb->ki_cookie, dio->submit.cookie);
+	WRITE_ONCE(iocb->private, dio->submit.last_queue);
+
 	if (!atomic_dec_and_test(&dio->ref)) {
 		if (!dio->wait_for_completion)
 			return -EIOCBQUEUED;
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index e47425071e65..60c2da41f0fc 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -1203,6 +1203,7 @@ const struct file_operations xfs_file_operations = {
 	.write_iter	= xfs_file_write_iter,
 	.splice_read	= generic_file_splice_read,
 	.splice_write	= iter_file_splice_write,
+	.iopoll		= iomap_dio_iopoll,
 	.unlocked_ioctl	= xfs_file_ioctl,
 #ifdef CONFIG_COMPAT
 	.compat_ioctl	= xfs_file_compat_ioctl,
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 9a4258154b25..0fefb5455bda 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -162,6 +162,7 @@ typedef int (iomap_dio_end_io_t)(struct kiocb *iocb, ssize_t ret,
 		unsigned flags);
 ssize_t iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 		const struct iomap_ops *ops, iomap_dio_end_io_t end_io);
+int iomap_dio_iopoll(struct kiocb *kiocb, bool spin);
 
 #ifdef CONFIG_SWAP
 struct file;
-- 
2.17.1

[PATCH 05/18] Add io_uring IO interface

[Jens Axboe]

The submission queue (SQ) and completion queue (CQ) rings are shared
between the application and the kernel. This eliminates the need to
copy data back and forth to submit and complete IO.

IO submissions use the io_uring_sqe data structure, and completions
are generated in the form of io_uring_sqe data structures. The SQ
ring is an index into the io_uring_sqe array, which makes it possible
to submit a batch of IOs without them being contiguous in the ring.
The CQ ring is always contiguous, as completion events are inherently
unordered, and hence any io_uring_cqe entry can point back to an
arbitrary submission.

Two new system calls are added for this:

io_uring_setup(entries, params)
	Sets up a context for doing async IO. On success, returns a file
	descriptor that the application can mmap to gain access to the
	SQ ring, CQ ring, and io_uring_sqes.

io_uring_enter(fd, to_submit, min_complete, flags)
	Initiates IO against the rings mapped to this fd, or waits for
	them to complete, or both. The behavior is controlled by the
	parameters passed in. If 'to_submit' is non-zero, then we'll
	try and submit new IO. If IORING_ENTER_GETEVENTS is set, the
	kernel will wait for 'min_complete' events, if they aren't
	already available. It's valid to set IORING_ENTER_GETEVENTS
	and 'min_complete' == 0 at the same time, this allows the
	kernel to return already completed events without waiting
	for them. This is useful only for polling, as for IRQ
	driven IO, the application can just check the CQ ring
	without entering the kernel.

With this setup, it's possible to do async IO with a single system
call. Future developments will enable polled IO with this interface,
and polled submission as well. The latter will enable an application
to do IO without doing ANY system calls at all.

For IRQ driven IO, an application only needs to enter the kernel for
completions if it wants to wait for them to occur.

Each io_uring is backed by a workqueue, to support buffered async IO
as well. We will only punt to an async context if the command would
need to wait for IO on the device side. Any data that can be accessed
directly in the page cache is done inline. This avoids the slowness
issue of usual threadpools, since cached data is accessed as quickly
as a sync interface.

Sample application: http://git.kernel.dk/cgit/fio/plain/t/io_uring.c

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 arch/x86/entry/syscalls/syscall_32.tbl |    2 +
 arch/x86/entry/syscalls/syscall_64.tbl |    2 +
 fs/Makefile                            |    1 +
 fs/io_uring.c                          | 1091 ++++++++++++++++++++++++
 include/linux/syscalls.h               |    5 +
 include/uapi/asm-generic/unistd.h      |    6 +-
 include/uapi/linux/io_uring.h          |   96 +++
 init/Kconfig                           |    9 +
 kernel/sys_ni.c                        |    3 +
 9 files changed, 1214 insertions(+), 1 deletion(-)
 create mode 100644 fs/io_uring.c
 create mode 100644 include/uapi/linux/io_uring.h

diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 3cf7b533b3d1..a6076d1e2154 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -398,3 +398,5 @@
 384	i386	arch_prctl		sys_arch_prctl			__ia32_compat_sys_arch_prctl
 385	i386	io_pgetevents		sys_io_pgetevents		__ia32_compat_sys_io_pgetevents
 386	i386	rseq			sys_rseq			__ia32_sys_rseq
+425	i386	io_uring_setup		sys_io_uring_setup		__ia32_compat_sys_io_uring_setup
+426	i386	io_uring_enter		sys_io_uring_enter		__ia32_sys_io_uring_enter
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index f0b1709a5ffb..6a32a430c8e0 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -343,6 +343,8 @@
 332	common	statx			__x64_sys_statx
 333	common	io_pgetevents		__x64_sys_io_pgetevents
 334	common	rseq			__x64_sys_rseq
+425	common	io_uring_setup		__x64_sys_io_uring_setup
+426	common	io_uring_enter		__x64_sys_io_uring_enter
 
 #
 # x32-specific system call numbers start at 512 to avoid cache impact
diff --git a/fs/Makefile b/fs/Makefile
index 293733f61594..8e15d6fc4340 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -30,6 +30,7 @@ obj-$(CONFIG_TIMERFD)		+= timerfd.o
 obj-$(CONFIG_EVENTFD)		+= eventfd.o
 obj-$(CONFIG_USERFAULTFD)	+= userfaultfd.o
 obj-$(CONFIG_AIO)               += aio.o
+obj-$(CONFIG_IO_URING)		+= io_uring.o
 obj-$(CONFIG_FS_DAX)		+= dax.o
 obj-$(CONFIG_FS_ENCRYPTION)	+= crypto/
 obj-$(CONFIG_FILE_LOCKING)      += locks.o
diff --git a/fs/io_uring.c b/fs/io_uring.c
new file mode 100644
index 000000000000..37ab16007aa6
--- /dev/null
+++ b/fs/io_uring.c
@@ -0,0 +1,1091 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Shared application/kernel submission and completion ring pairs, for
+ * supporting fast/efficient IO.
+ *
+ * Copyright (C) 2018-2019 Jens Axboe
+ */
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/errno.h>
+#include <linux/syscalls.h>
+#include <linux/compat.h>
+#include <linux/refcount.h>
+#include <linux/uio.h>
+
+#include <linux/sched/signal.h>
+#include <linux/fs.h>
+#include <linux/file.h>
+#include <linux/fdtable.h>
+#include <linux/mm.h>
+#include <linux/mman.h>
+#include <linux/mmu_context.h>
+#include <linux/percpu.h>
+#include <linux/slab.h>
+#include <linux/workqueue.h>
+#include <linux/blkdev.h>
+#include <linux/anon_inodes.h>
+#include <linux/sched/mm.h>
+
+#include <linux/uaccess.h>
+#include <linux/nospec.h>
+
+#include <uapi/linux/io_uring.h>
+
+#include "internal.h"
+
+struct io_uring {
+	u32 head ____cacheline_aligned_in_smp;
+	u32 tail ____cacheline_aligned_in_smp;
+};
+
+struct io_sq_ring {
+	struct io_uring		r;
+	u32			ring_mask;
+	u32			ring_entries;
+	u32			dropped;
+	u32			flags;
+	u32			array[];
+};
+
+struct io_cq_ring {
+	struct io_uring		r;
+	u32			ring_mask;
+	u32			ring_entries;
+	u32			overflow;
+	struct io_uring_cqe	cqes[];
+};
+
+struct io_ring_ctx {
+	struct {
+		struct percpu_ref	refs;
+	} ____cacheline_aligned_in_smp;
+
+	struct {
+		unsigned int		flags;
+		bool			compat;
+
+		/* SQ ring */
+		struct io_sq_ring	*sq_ring;
+		unsigned		cached_sq_head;
+		unsigned		sq_entries;
+		unsigned		sq_mask;
+		unsigned		sq_thread_cpu;
+		struct io_uring_sqe	*sq_sqes;
+	} ____cacheline_aligned_in_smp;
+
+	/* IO offload */
+	struct workqueue_struct	*sqo_wq;
+	struct mm_struct	*sqo_mm;
+	struct files_struct	*sqo_files;
+
+	struct {
+		/* CQ ring */
+		struct io_cq_ring	*cq_ring;
+		unsigned		cached_cq_tail;
+		unsigned		cq_entries;
+		unsigned		cq_mask;
+		struct wait_queue_head	cq_wait;
+		struct fasync_struct	*cq_fasync;
+	} ____cacheline_aligned_in_smp;
+
+	struct user_struct	*user;
+
+	struct completion	ctx_done;
+
+	struct {
+		struct mutex		uring_lock;
+		wait_queue_head_t	wait;
+	} ____cacheline_aligned_in_smp;
+
+	struct {
+		spinlock_t		completion_lock;
+	} ____cacheline_aligned_in_smp;
+};
+
+struct sqe_submit {
+	const struct io_uring_sqe *sqe;
+	unsigned index;
+};
+
+struct io_kiocb {
+	union {
+		struct kiocb		rw;
+		struct sqe_submit	submit;
+	};
+
+	struct io_ring_ctx	*ctx;
+	struct list_head	list;
+	unsigned int		flags;
+#define REQ_F_FORCE_NONBLOCK	1	/* inline submission attempt */
+	u64			user_data;
+
+	struct work_struct	work;
+};
+
+#define IO_PLUG_THRESHOLD		2
+
+static struct kmem_cache *req_cachep;
+
+static const struct file_operations io_uring_fops;
+
+static void io_ring_ctx_ref_free(struct percpu_ref *ref)
+{
+	struct io_ring_ctx *ctx = container_of(ref, struct io_ring_ctx, refs);
+
+	complete(&ctx->ctx_done);
+}
+
+static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
+{
+	struct io_ring_ctx *ctx;
+
+	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
+	if (!ctx)
+		return NULL;
+
+	if (percpu_ref_init(&ctx->refs, io_ring_ctx_ref_free, 0, GFP_KERNEL)) {
+		kfree(ctx);
+		return NULL;
+	}
+
+	ctx->flags = p->flags;
+	init_waitqueue_head(&ctx->cq_wait);
+	init_completion(&ctx->ctx_done);
+	mutex_init(&ctx->uring_lock);
+	init_waitqueue_head(&ctx->wait);
+	spin_lock_init(&ctx->completion_lock);
+	return ctx;
+}
+
+static void io_commit_cqring(struct io_ring_ctx *ctx)
+{
+	struct io_cq_ring *ring = ctx->cq_ring;
+
+	if (ctx->cached_cq_tail != ring->r.tail) {
+		/* order cqe stores with ring update */
+		smp_wmb();
+		ring->r.tail = ctx->cached_cq_tail;
+		/* write side barrier of tail update, app has read side */
+		smp_wmb();
+
+		if (wq_has_sleeper(&ctx->cq_wait)) {
+			wake_up_interruptible(&ctx->cq_wait);
+			kill_fasync(&ctx->cq_fasync, SIGIO, POLL_IN);
+		}
+	}
+}
+
+static struct io_uring_cqe *io_get_cqring(struct io_ring_ctx *ctx)
+{
+	struct io_cq_ring *ring = ctx->cq_ring;
+	unsigned tail;
+
+	tail = ctx->cached_cq_tail;
+	smp_rmb();
+	if (tail + 1 == READ_ONCE(ring->r.head))
+		return NULL;
+
+	ctx->cached_cq_tail++;
+	return &ring->cqes[tail & ctx->cq_mask];
+}
+
+static void __io_cqring_add_event(struct io_ring_ctx *ctx, u64 ki_user_data,
+				  long res, unsigned ev_flags)
+{
+	struct io_uring_cqe *cqe;
+
+	/*
+	 * If we can't get a cq entry, userspace overflowed the
+	 * submission (by quite a lot). Increment the overflow count in
+	 * the ring.
+	 */
+	cqe = io_get_cqring(ctx);
+	if (cqe) {
+		cqe->user_data = ki_user_data;
+		cqe->res = res;
+		cqe->flags = ev_flags;
+		io_commit_cqring(ctx);
+	} else
+		ctx->cq_ring->overflow++;
+
+	if (waitqueue_active(&ctx->wait))
+		wake_up(&ctx->wait);
+}
+
+static void io_cqring_add_event(struct io_ring_ctx *ctx, u64 ki_user_data,
+				long res, unsigned ev_flags)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&ctx->completion_lock, flags);
+	__io_cqring_add_event(ctx, ki_user_data, res, ev_flags);
+	spin_unlock_irqrestore(&ctx->completion_lock, flags);
+}
+
+static void io_ring_drop_ctx_refs(struct io_ring_ctx *ctx, unsigned refs)
+{
+	percpu_ref_put_many(&ctx->refs, refs);
+
+	if (waitqueue_active(&ctx->wait))
+		wake_up(&ctx->wait);
+}
+
+static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx)
+{
+	struct io_kiocb *req;
+
+	/* safe to use the non tryget, as we're inside ring ref already */
+	percpu_ref_get(&ctx->refs);
+
+	req = kmem_cache_alloc(req_cachep, GFP_ATOMIC | __GFP_NOWARN);
+	if (req) {
+		req->ctx = ctx;
+		req->flags = 0;
+		return req;
+	}
+
+	io_ring_drop_ctx_refs(ctx, 1);
+	return NULL;
+}
+
+static void io_free_req(struct io_kiocb *req)
+{
+	io_ring_drop_ctx_refs(req->ctx, 1);
+	kmem_cache_free(req_cachep, req);
+}
+
+static void kiocb_end_write(struct kiocb *kiocb)
+{
+	if (kiocb->ki_flags & IOCB_WRITE) {
+		struct inode *inode = file_inode(kiocb->ki_filp);
+
+		/*
+		 * Tell lockdep we inherited freeze protection from submission
+		 * thread.
+		 */
+		if (S_ISREG(inode->i_mode))
+			__sb_writers_acquired(inode->i_sb, SB_FREEZE_WRITE);
+		file_end_write(kiocb->ki_filp);
+	}
+}
+
+static void io_complete_rw(struct kiocb *kiocb, long res, long res2)
+{
+	struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw);
+
+	kiocb_end_write(kiocb);
+
+	fput(kiocb->ki_filp);
+	io_cqring_add_event(req->ctx, req->user_data, res, 0);
+	io_free_req(req);
+}
+
+static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
+		      bool force_nonblock)
+{
+	struct kiocb *kiocb = &req->rw;
+	int ret;
+
+	kiocb->ki_filp = fget(sqe->fd);
+	if (unlikely(!kiocb->ki_filp))
+		return -EBADF;
+	kiocb->ki_pos = sqe->off;
+	kiocb->ki_flags = iocb_flags(kiocb->ki_filp);
+	kiocb->ki_hint = ki_hint_validate(file_write_hint(kiocb->ki_filp));
+	if (sqe->ioprio) {
+		ret = ioprio_check_cap(sqe->ioprio);
+		if (ret)
+			goto out_fput;
+
+		kiocb->ki_ioprio = sqe->ioprio;
+	} else
+		kiocb->ki_ioprio = get_current_ioprio();
+
+	ret = kiocb_set_rw_flags(kiocb, sqe->rw_flags);
+	if (unlikely(ret))
+		goto out_fput;
+	if (force_nonblock) {
+		kiocb->ki_flags |= IOCB_NOWAIT;
+		req->flags |= REQ_F_FORCE_NONBLOCK;
+	}
+	if (kiocb->ki_flags & IOCB_HIPRI) {
+		ret = -EINVAL;
+		goto out_fput;
+	}
+
+	kiocb->ki_complete = io_complete_rw;
+	return 0;
+out_fput:
+	fput(kiocb->ki_filp);
+	return ret;
+}
+
+static inline void io_rw_done(struct kiocb *kiocb, ssize_t ret)
+{
+	switch (ret) {
+	case -EIOCBQUEUED:
+		break;
+	case -ERESTARTSYS:
+	case -ERESTARTNOINTR:
+	case -ERESTARTNOHAND:
+	case -ERESTART_RESTARTBLOCK:
+		/*
+		 * We can't just restart the syscall, since previously
+		 * submitted sqes may already be in progress. Just fail this
+		 * IO with EINTR.
+		 */
+		ret = -EINTR;
+		/* fall through */
+	default:
+		kiocb->ki_complete(kiocb, ret, 0);
+	}
+}
+
+static int io_import_iovec(struct io_ring_ctx *ctx, int rw,
+			   const struct io_uring_sqe *sqe,
+			   struct iovec **iovec, struct iov_iter *iter)
+{
+	void __user *buf = u64_to_user_ptr(sqe->addr);
+
+#ifdef CONFIG_COMPAT
+	if (ctx->compat)
+		return compat_import_iovec(rw, buf, sqe->len, UIO_FASTIOV,
+						iovec, iter);
+#endif
+	return import_iovec(rw, buf, sqe->len, UIO_FASTIOV, iovec, iter);
+}
+
+static ssize_t io_read(struct io_kiocb *req, const struct io_uring_sqe *sqe,
+		       bool force_nonblock)
+{
+	struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
+	struct kiocb *kiocb = &req->rw;
+	struct iov_iter iter;
+	struct file *file;
+	ssize_t ret;
+
+	ret = io_prep_rw(req, sqe, force_nonblock);
+	if (ret)
+		return ret;
+	file = kiocb->ki_filp;
+
+	ret = -EBADF;
+	if (unlikely(!(file->f_mode & FMODE_READ)))
+		goto out_fput;
+	ret = -EINVAL;
+	if (unlikely(!file->f_op->read_iter))
+		goto out_fput;
+
+	ret = io_import_iovec(req->ctx, READ, sqe, &iovec, &iter);
+	if (ret)
+		goto out_fput;
+
+	ret = rw_verify_area(READ, file, &kiocb->ki_pos, iov_iter_count(&iter));
+	if (!ret) {
+		ssize_t ret2;
+
+		/* Catch -EAGAIN return for forced non-blocking submission */
+		ret2 = call_read_iter(file, kiocb, &iter);
+		if (!force_nonblock || ret2 != -EAGAIN)
+			io_rw_done(kiocb, ret2);
+		else
+			ret = -EAGAIN;
+	}
+	kfree(iovec);
+out_fput:
+	if (unlikely(ret))
+		fput(file);
+	return ret;
+}
+
+static ssize_t io_write(struct io_kiocb *req, const struct io_uring_sqe *sqe,
+			bool force_nonblock)
+{
+	struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
+	struct kiocb *kiocb = &req->rw;
+	struct iov_iter iter;
+	struct file *file;
+	ssize_t ret;
+
+	ret = io_prep_rw(req, sqe, force_nonblock);
+	if (ret)
+		return ret;
+	file = kiocb->ki_filp;
+
+	ret = -EAGAIN;
+	if (force_nonblock && !(kiocb->ki_flags & IOCB_DIRECT))
+		goto out_fput;
+
+	ret = -EBADF;
+	if (unlikely(!(file->f_mode & FMODE_WRITE)))
+		goto out_fput;
+	ret = -EINVAL;
+	if (unlikely(!file->f_op->write_iter))
+		goto out_fput;
+
+	ret = io_import_iovec(req->ctx, WRITE, sqe, &iovec, &iter);
+	if (ret)
+		goto out_fput;
+
+	ret = rw_verify_area(WRITE, file, &kiocb->ki_pos,
+				iov_iter_count(&iter));
+	if (!ret) {
+		/*
+		 * Open-code file_start_write here to grab freeze protection,
+		 * which will be released by another thread in
+		 * io_complete_rw().  Fool lockdep by telling it the lock got
+		 * released so that it doesn't complain about the held lock when
+		 * we return to userspace.
+		 */
+		if (S_ISREG(file_inode(file)->i_mode)) {
+			__sb_start_write(file_inode(file)->i_sb,
+						SB_FREEZE_WRITE, true);
+			__sb_writers_release(file_inode(file)->i_sb,
+						SB_FREEZE_WRITE);
+		}
+		kiocb->ki_flags |= IOCB_WRITE;
+		io_rw_done(kiocb, call_write_iter(file, kiocb, &iter));
+	}
+	kfree(iovec);
+out_fput:
+	if (unlikely(ret))
+		fput(file);
+	return ret;
+}
+
+/*
+ * IORING_OP_NOP just posts a completion event, nothing else.
+ */
+static int io_nop(struct io_kiocb *req, const struct io_uring_sqe *sqe)
+{
+	struct io_ring_ctx *ctx = req->ctx;
+
+	__io_cqring_add_event(ctx, sqe->user_data, 0, 0);
+	io_free_req(req);
+	return 0;
+}
+
+static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
+			   struct sqe_submit *s, bool force_nonblock)
+{
+	const struct io_uring_sqe *sqe = s->sqe;
+	ssize_t ret;
+
+	if (unlikely(s->index >= ctx->sq_entries))
+		return -EINVAL;
+	req->user_data = sqe->user_data;
+
+	ret = -EINVAL;
+	switch (sqe->opcode) {
+	case IORING_OP_NOP:
+		ret = io_nop(req, sqe);
+		break;
+	case IORING_OP_READV:
+		ret = io_read(req, sqe, force_nonblock);
+		break;
+	case IORING_OP_WRITEV:
+		ret = io_write(req, sqe, force_nonblock);
+		break;
+	default:
+		ret = -EINVAL;
+		break;
+	}
+
+	return ret;
+}
+
+static void io_sq_wq_submit_work(struct work_struct *work)
+{
+	struct io_kiocb *req = container_of(work, struct io_kiocb, work);
+	struct sqe_submit *s = &req->submit;
+	u64 user_data = s->sqe->user_data;
+	struct io_ring_ctx *ctx = req->ctx;
+	mm_segment_t old_fs = get_fs();
+	struct files_struct *old_files;
+	int ret;
+
+	 /* Ensure we clear previously set forced non-block flag */
+	req->flags &= ~REQ_F_FORCE_NONBLOCK;
+
+	old_files = current->files;
+	current->files = ctx->sqo_files;
+
+	if (!mmget_not_zero(ctx->sqo_mm)) {
+		ret = -EFAULT;
+		goto err;
+	}
+
+	use_mm(ctx->sqo_mm);
+	set_fs(USER_DS);
+
+	ret = __io_submit_sqe(ctx, req, s, false);
+
+	set_fs(old_fs);
+	unuse_mm(ctx->sqo_mm);
+	mmput(ctx->sqo_mm);
+err:
+	if (ret) {
+		io_cqring_add_event(ctx, user_data, ret, 0);
+		io_free_req(req);
+	}
+	current->files = old_files;
+}
+
+static int io_submit_sqe(struct io_ring_ctx *ctx, struct sqe_submit *s)
+{
+	struct io_kiocb *req;
+	ssize_t ret;
+
+	/* enforce forwards compatibility on users */
+	if (unlikely(s->sqe->flags))
+		return -EINVAL;
+
+	req = io_get_req(ctx);
+	if (unlikely(!req))
+		return -EAGAIN;
+
+	ret = __io_submit_sqe(ctx, req, s, true);
+	if (ret == -EAGAIN) {
+		memcpy(&req->submit, s, sizeof(*s));
+		INIT_WORK(&req->work, io_sq_wq_submit_work);
+		queue_work(ctx->sqo_wq, &req->work);
+		ret = 0;
+	}
+	if (ret)
+		io_free_req(req);
+
+	return ret;
+}
+
+static void io_commit_sqring(struct io_ring_ctx *ctx)
+{
+	struct io_sq_ring *ring = ctx->sq_ring;
+
+	if (ctx->cached_sq_head != ring->r.head) {
+		ring->r.head = ctx->cached_sq_head;
+		/* write side barrier of head update, app has read side */
+		smp_wmb();
+	}
+}
+
+/*
+ * Undo last io_get_sqring()
+ */
+static void io_drop_sqring(struct io_ring_ctx *ctx)
+{
+	ctx->cached_sq_head--;
+}
+
+static bool io_get_sqring(struct io_ring_ctx *ctx, struct sqe_submit *s)
+{
+	struct io_sq_ring *ring = ctx->sq_ring;
+	unsigned head;
+
+	head = ctx->cached_sq_head;
+	smp_rmb();
+	if (head == READ_ONCE(ring->r.tail))
+		return false;
+
+	head = ring->array[head & ctx->sq_mask];
+	if (head < ctx->sq_entries) {
+		s->index = head;
+		s->sqe = &ctx->sq_sqes[head];
+		ctx->cached_sq_head++;
+		return true;
+	}
+
+	/* drop invalid entries */
+	ctx->cached_sq_head++;
+	ring->dropped++;
+	smp_wmb();
+	return false;
+}
+
+static int io_ring_submit(struct io_ring_ctx *ctx, unsigned int to_submit)
+{
+	int i, ret = 0, submit = 0;
+	struct blk_plug plug;
+
+	if (to_submit > IO_PLUG_THRESHOLD)
+		blk_start_plug(&plug);
+
+	for (i = 0; i < to_submit; i++) {
+		struct sqe_submit s;
+
+		if (!io_get_sqring(ctx, &s))
+			break;
+
+		ret = io_submit_sqe(ctx, &s);
+		if (ret) {
+			io_drop_sqring(ctx);
+			break;
+		}
+
+		submit++;
+	}
+	io_commit_sqring(ctx);
+
+	if (to_submit > IO_PLUG_THRESHOLD)
+		blk_finish_plug(&plug);
+
+	return submit ? submit : ret;
+}
+
+/*
+ * Wait until events become available, if we don't already have some. The
+ * application must reap them itself, as they reside on the shared cq ring.
+ */
+static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events)
+{
+	struct io_cq_ring *ring = ctx->cq_ring;
+	DEFINE_WAIT(wait);
+	int ret = 0;
+
+	smp_rmb();
+	if (ring->r.head != ring->r.tail)
+		return 0;
+	if (!min_events)
+		return 0;
+
+	do {
+		prepare_to_wait(&ctx->wait, &wait, TASK_INTERRUPTIBLE);
+
+		ret = 0;
+		smp_rmb();
+		if (ring->r.head != ring->r.tail)
+			break;
+
+		schedule();
+
+		ret = -EINTR;
+		if (signal_pending(current))
+			break;
+	} while (1);
+
+	finish_wait(&ctx->wait, &wait);
+	return ring->r.head == ring->r.tail ? ret : 0;
+}
+
+static int __io_uring_enter(struct io_ring_ctx *ctx, unsigned to_submit,
+			    unsigned min_complete, unsigned flags)
+{
+	int ret = 0;
+
+	if (to_submit) {
+		ret = io_ring_submit(ctx, to_submit);
+		if (ret < 0)
+			return ret;
+	}
+	if (flags & IORING_ENTER_GETEVENTS) {
+		int get_ret;
+
+		if (!ret && to_submit)
+			min_complete = 0;
+
+		get_ret = io_cqring_wait(ctx, min_complete);
+		if (get_ret < 0 && !ret)
+			ret = get_ret;
+	}
+
+	return ret;
+}
+
+static int io_sq_offload_start(struct io_ring_ctx *ctx)
+{
+	int ret;
+
+	ctx->sqo_mm = current->mm;
+
+	/*
+	 * This is safe since 'current' has the fd installed, and if that gets
+	 * closed on exit, then fops->release() is invoked which waits for the
+	 * async contexts to flush and exit before exiting.
+	 */
+	ret = -EBADF;
+	ctx->sqo_files = current->files;
+	if (!ctx->sqo_files)
+		goto err;
+
+	/* Do QD, or 2 * CPUS, whatever is smallest */
+	ctx->sqo_wq = alloc_workqueue("io_ring-wq", WQ_UNBOUND | WQ_FREEZABLE,
+			min(ctx->sq_entries - 1, 2 * num_online_cpus()));
+	if (!ctx->sqo_wq) {
+		ret = -ENOMEM;
+		goto err;
+	}
+
+	return 0;
+err:
+	if (ctx->sqo_files)
+		ctx->sqo_files = NULL;
+	ctx->sqo_mm = NULL;
+	return ret;
+}
+
+static void io_sq_offload_stop(struct io_ring_ctx *ctx)
+{
+	if (ctx->sqo_wq) {
+		destroy_workqueue(ctx->sqo_wq);
+		ctx->sqo_wq = NULL;
+	}
+}
+
+static void __io_unaccount_mem(struct user_struct *user, unsigned long nr_pages)
+{
+	atomic_long_sub(nr_pages, &user->locked_vm);
+}
+
+static void io_unaccount_mem(struct io_ring_ctx *ctx, unsigned long nr_pages)
+{
+	if (ctx->user)
+		__io_unaccount_mem(ctx->user, nr_pages);
+}
+
+static int __io_account_mem(struct user_struct *user, unsigned long nr_pages)
+{
+	unsigned long page_limit, cur_pages, new_pages;
+
+	/* Don't allow more pages than we can safely lock */
+	page_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
+
+	do {
+		cur_pages = atomic_long_read(&user->locked_vm);
+		new_pages = cur_pages + nr_pages;
+		if (new_pages > page_limit)
+			return -ENOMEM;
+	} while (atomic_long_cmpxchg(&user->locked_vm, cur_pages,
+					new_pages) != cur_pages);
+
+	return 0;
+}
+
+static unsigned long ring_pages(unsigned sq_entries, unsigned cq_entries)
+{
+	struct io_sq_ring *sq_ring;
+	struct io_cq_ring *cq_ring;
+	size_t bytes;
+
+	bytes = struct_size(sq_ring, array, sq_entries);
+	bytes += array_size(sizeof(struct io_uring_sqe), sq_entries);
+	bytes += struct_size(cq_ring, cqes, cq_entries);
+
+	return (bytes + PAGE_SIZE - 1) / PAGE_SIZE;
+}
+
+static void io_free_scq_urings(struct io_ring_ctx *ctx)
+{
+	if (ctx->sq_ring) {
+		page_frag_free(ctx->sq_ring);
+		ctx->sq_ring = NULL;
+	}
+	if (ctx->sq_sqes) {
+		page_frag_free(ctx->sq_sqes);
+		ctx->sq_sqes = NULL;
+	}
+	if (ctx->cq_ring) {
+		page_frag_free(ctx->cq_ring);
+		ctx->cq_ring = NULL;
+	}
+}
+
+static void io_ring_ctx_free(struct io_ring_ctx *ctx)
+{
+	io_sq_offload_stop(ctx);
+	io_free_scq_urings(ctx);
+	percpu_ref_exit(&ctx->refs);
+	io_unaccount_mem(ctx, ring_pages(ctx->sq_entries, ctx->cq_entries));
+	kfree(ctx);
+}
+
+static __poll_t io_uring_poll(struct file *file, poll_table *wait)
+{
+	struct io_ring_ctx *ctx = file->private_data;
+	__poll_t mask = 0;
+
+	poll_wait(file, &ctx->cq_wait, wait);
+	smp_rmb();
+	if (ctx->sq_ring->r.tail + 1 != ctx->cached_sq_head)
+		mask |= EPOLLOUT | EPOLLWRNORM;
+	if (ctx->cq_ring->r.head != ctx->cached_cq_tail)
+		mask |= EPOLLIN | EPOLLRDNORM;
+
+	return mask;
+}
+
+static int io_uring_fasync(int fd, struct file *file, int on)
+{
+	struct io_ring_ctx *ctx = file->private_data;
+
+	return fasync_helper(fd, file, on, &ctx->cq_fasync);
+}
+
+static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
+{
+	mutex_lock(&ctx->uring_lock);
+	percpu_ref_kill(&ctx->refs);
+	mutex_unlock(&ctx->uring_lock);
+
+	wait_for_completion(&ctx->ctx_done);
+	io_ring_ctx_free(ctx);
+}
+
+static int io_uring_release(struct inode *inode, struct file *file)
+{
+	struct io_ring_ctx *ctx = file->private_data;
+
+	file->private_data = NULL;
+	io_ring_ctx_wait_and_kill(ctx);
+	return 0;
+}
+
+static int io_uring_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	loff_t offset = (loff_t) vma->vm_pgoff << PAGE_SHIFT;
+	unsigned long sz = vma->vm_end - vma->vm_start;
+	struct io_ring_ctx *ctx = file->private_data;
+	unsigned long pfn;
+	struct page *page;
+	void *ptr;
+
+	switch (offset) {
+	case IORING_OFF_SQ_RING:
+		ptr = ctx->sq_ring;
+		break;
+	case IORING_OFF_SQES:
+		ptr = ctx->sq_sqes;
+		break;
+	case IORING_OFF_CQ_RING:
+		ptr = ctx->cq_ring;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	page = virt_to_head_page(ptr);
+	if (sz > (PAGE_SIZE << compound_order(page)))
+		return -EINVAL;
+
+	pfn = virt_to_phys(ptr) >> PAGE_SHIFT;
+	return remap_pfn_range(vma, vma->vm_start, pfn, sz, vma->vm_page_prot);
+}
+
+SYSCALL_DEFINE4(io_uring_enter, unsigned int, fd, u32, to_submit,
+		u32, min_complete, u32, flags)
+{
+	struct io_ring_ctx *ctx;
+	long ret = -EBADF;
+	struct fd f;
+
+	f = fdget(fd);
+	if (!f.file)
+		return -EBADF;
+
+	ret = -EOPNOTSUPP;
+	if (f.file->f_op != &io_uring_fops)
+		goto out_fput;
+
+	ret = -ENXIO;
+	ctx = f.file->private_data;
+	if (!percpu_ref_tryget(&ctx->refs))
+		goto out_fput;
+
+	ret = -EBUSY;
+	if (mutex_trylock(&ctx->uring_lock)) {
+		ret = __io_uring_enter(ctx, to_submit, min_complete, flags);
+		mutex_unlock(&ctx->uring_lock);
+	}
+	io_ring_drop_ctx_refs(ctx, 1);
+out_fput:
+	fdput(f);
+	return ret;
+}
+
+static const struct file_operations io_uring_fops = {
+	.release	= io_uring_release,
+	.mmap		= io_uring_mmap,
+	.poll		= io_uring_poll,
+	.fasync		= io_uring_fasync,
+};
+
+static void *io_mem_alloc(size_t size)
+{
+	gfp_t gfp_flags = GFP_KERNEL | __GFP_ZERO | __GFP_NOWARN | __GFP_COMP |
+				__GFP_NORETRY;
+
+	return (void *) __get_free_pages(gfp_flags, get_order(size));
+}
+
+static int io_allocate_scq_urings(struct io_ring_ctx *ctx,
+				  struct io_uring_params *p)
+{
+	struct io_sq_ring *sq_ring;
+	struct io_cq_ring *cq_ring;
+	size_t size;
+	int ret;
+
+	sq_ring = io_mem_alloc(struct_size(sq_ring, array, p->sq_entries));
+	if (!sq_ring)
+		return -ENOMEM;
+
+	ctx->sq_ring = sq_ring;
+	sq_ring->ring_mask = p->sq_entries - 1;
+	sq_ring->ring_entries = p->sq_entries;
+	ctx->sq_mask = sq_ring->ring_mask;
+	ctx->sq_entries = sq_ring->ring_entries;
+
+	ret = -EOVERFLOW;
+	size = array_size(sizeof(struct io_uring_sqe), p->sq_entries);
+	if (size == SIZE_MAX)
+		goto err;
+	ret = -ENOMEM;
+	ctx->sq_sqes = io_mem_alloc(size);
+	if (!ctx->sq_sqes)
+		goto err;
+
+	cq_ring = io_mem_alloc(struct_size(cq_ring, cqes, p->cq_entries));
+	if (!cq_ring)
+		goto err;
+
+	ctx->cq_ring = cq_ring;
+	cq_ring->ring_mask = p->cq_entries - 1;
+	cq_ring->ring_entries = p->cq_entries;
+	ctx->cq_mask = cq_ring->ring_mask;
+	ctx->cq_entries = cq_ring->ring_entries;
+	return 0;
+err:
+	io_free_scq_urings(ctx);
+	return ret;
+}
+
+static void io_fill_offsets(struct io_uring_params *p)
+{
+	memset(&p->sq_off, 0, sizeof(p->sq_off));
+	p->sq_off.head = offsetof(struct io_sq_ring, r.head);
+	p->sq_off.tail = offsetof(struct io_sq_ring, r.tail);
+	p->sq_off.ring_mask = offsetof(struct io_sq_ring, ring_mask);
+	p->sq_off.ring_entries = offsetof(struct io_sq_ring, ring_entries);
+	p->sq_off.flags = offsetof(struct io_sq_ring, flags);
+	p->sq_off.dropped = offsetof(struct io_sq_ring, dropped);
+	p->sq_off.array = offsetof(struct io_sq_ring, array);
+
+	memset(&p->cq_off, 0, sizeof(p->cq_off));
+	p->cq_off.head = offsetof(struct io_cq_ring, r.head);
+	p->cq_off.tail = offsetof(struct io_cq_ring, r.tail);
+	p->cq_off.ring_mask = offsetof(struct io_cq_ring, ring_mask);
+	p->cq_off.ring_entries = offsetof(struct io_cq_ring, ring_entries);
+	p->cq_off.overflow = offsetof(struct io_cq_ring, overflow);
+	p->cq_off.cqes = offsetof(struct io_cq_ring, cqes);
+}
+
+static int io_uring_create(unsigned entries, struct io_uring_params *p,
+			   bool compat)
+{
+	struct user_struct *user = NULL;
+	struct io_ring_ctx *ctx;
+	int ret;
+
+	if (!entries || entries > IORING_MAX_ENTRIES)
+		return -EINVAL;
+
+	/*
+	 * Use twice as many entries for the CQ ring. It's possible for the
+	 * application to drive a higher depth than the size of the SQ ring,
+	 * since the sqes are only used at submission time. This allows for
+	 * some flexibility in overcommitting a bit.
+	 */
+	p->sq_entries = roundup_pow_of_two(entries);
+	p->cq_entries = 2 * p->sq_entries;
+
+	if (!capable(CAP_IPC_LOCK)) {
+		user = get_uid(current_user());
+		ret = __io_account_mem(user, ring_pages(p->sq_entries,
+							p->cq_entries));
+		if (ret) {
+			free_uid(user);
+			return ret;
+		}
+	}
+
+	ctx = io_ring_ctx_alloc(p);
+	if (!ctx) {
+		__io_unaccount_mem(user, ring_pages(p->sq_entries,
+							p->cq_entries));
+		free_uid(user);
+		return -ENOMEM;
+	}
+	ctx->compat = compat;
+	ctx->user = user;
+
+	ret = io_allocate_scq_urings(ctx, p);
+	if (ret)
+		goto err;
+
+	ret = io_sq_offload_start(ctx);
+	if (ret)
+		goto err;
+
+	ret = anon_inode_getfd("[io_uring]", &io_uring_fops, ctx,
+				O_RDWR | O_CLOEXEC);
+	if (ret < 0)
+		goto err;
+
+	io_fill_offsets(p);
+	return ret;
+err:
+	io_ring_ctx_wait_and_kill(ctx);
+	return ret;
+}
+
+/*
+ * Sets up an aio uring context, and returns the fd. Applications asks for a
+ * ring size, we return the actual sq/cq ring sizes (among other things) in the
+ * params structure passed in.
+ */
+static long io_uring_setup(u32 entries, struct io_uring_params __user *params,
+			   bool compat)
+{
+	struct io_uring_params p;
+	long ret;
+	int i;
+
+	if (copy_from_user(&p, params, sizeof(p)))
+		return -EFAULT;
+	for (i = 0; i < ARRAY_SIZE(p.resv); i++) {
+		if (p.resv[i])
+			return -EINVAL;
+	}
+
+	if (p.flags)
+		return -EINVAL;
+
+	ret = io_uring_create(entries, &p, compat);
+	if (ret < 0)
+		return ret;
+
+	if (copy_to_user(params, &p, sizeof(p)))
+		return -EFAULT;
+
+	return ret;
+}
+
+SYSCALL_DEFINE2(io_uring_setup, u32, entries,
+		struct io_uring_params __user *, params)
+{
+	return io_uring_setup(entries, params, false);
+}
+
+#ifdef CONFIG_COMPAT
+COMPAT_SYSCALL_DEFINE2(io_uring_setup, u32, entries,
+		       struct io_uring_params __user *, params)
+{
+	return io_uring_setup(entries, params, true);
+}
+#endif
+
+static int __init io_uring_init(void)
+{
+	req_cachep = KMEM_CACHE(io_kiocb, SLAB_HWCACHE_ALIGN | SLAB_PANIC);
+	return 0;
+};
+__initcall(io_uring_init);
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 257cccba3062..542757a4c898 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -69,6 +69,7 @@ struct file_handle;
 struct sigaltstack;
 struct rseq;
 union bpf_attr;
+struct io_uring_params;
 
 #include <linux/types.h>
 #include <linux/aio_abi.h>
@@ -309,6 +310,10 @@ asmlinkage long sys_io_pgetevents_time32(aio_context_t ctx_id,
 				struct io_event __user *events,
 				struct old_timespec32 __user *timeout,
 				const struct __aio_sigset *sig);
+asmlinkage long sys_io_uring_setup(u32 entries,
+				struct io_uring_params __user *p);
+asmlinkage long sys_io_uring_enter(unsigned int fd, u32 to_submit,
+				u32 min_complete, u32 flags);
 
 /* fs/xattr.c */
 asmlinkage long sys_setxattr(const char __user *path, const char __user *name,
diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index d90127298f12..87871e7b7ea7 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -740,9 +740,13 @@ __SC_COMP(__NR_io_pgetevents, sys_io_pgetevents, compat_sys_io_pgetevents)
 __SYSCALL(__NR_rseq, sys_rseq)
 #define __NR_kexec_file_load 294
 __SYSCALL(__NR_kexec_file_load,     sys_kexec_file_load)
+#define __NR_io_uring_setup 425
+__SYSCALL(__NR_io_uring_setup, sys_io_uring_setup)
+#define __NR_io_uring_enter 426
+__SYSCALL(__NR_io_uring_enter, sys_io_uring_enter)
 
 #undef __NR_syscalls
-#define __NR_syscalls 295
+#define __NR_syscalls 427
 
 /*
  * 32 bit systems traditionally used different
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
new file mode 100644
index 000000000000..ce65db9269a8
--- /dev/null
+++ b/include/uapi/linux/io_uring.h
@@ -0,0 +1,96 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * Header file for the io_uring interface.
+ *
+ * Copyright (C) 2019 Jens Axboe
+ * Copyright (C) 2019 Christoph Hellwig
+ */
+#ifndef LINUX_IO_URING_H
+#define LINUX_IO_URING_H
+
+#include <linux/fs.h>
+#include <linux/types.h>
+
+#define IORING_MAX_ENTRIES	4096
+
+/*
+ * IO submission data structure (Submission Queue Entry)
+ */
+struct io_uring_sqe {
+	__u8	opcode;		/* type of operation for this sqe */
+	__u8	flags;		/* as of now unused */
+	__u16	ioprio;		/* ioprio for the request */
+	__s32	fd;		/* file descriptor to do IO on */
+	__u64	off;		/* offset into file */
+	__u64	addr;		/* pointer to buffer or iovecs */
+	__u32	len;		/* buffer size or number of iovecs */
+	union {
+		__kernel_rwf_t	rw_flags;
+		__u32		__resv;
+	};
+	__u64	user_data;	/* data to be passed back at completion time */
+	__u64	__pad2[3];
+};
+
+#define IORING_OP_NOP		0
+#define IORING_OP_READV		1
+#define IORING_OP_WRITEV	2
+
+/*
+ * IO completion data structure (Completion Queue Entry)
+ */
+struct io_uring_cqe {
+	__u64	user_data;	/* sqe->data submission passed back */
+	__s32	res;		/* result code for this event */
+	__u32	flags;
+};
+
+/*
+ * Magic offsets for the application to mmap the data it needs
+ */
+#define IORING_OFF_SQ_RING		0ULL
+#define IORING_OFF_CQ_RING		0x8000000ULL
+#define IORING_OFF_SQES			0x10000000ULL
+
+/*
+ * Filled with the offset for mmap(2)
+ */
+struct io_sqring_offsets {
+	__u32 head;
+	__u32 tail;
+	__u32 ring_mask;
+	__u32 ring_entries;
+	__u32 flags;
+	__u32 dropped;
+	__u32 array;
+	__u32 resv[3];
+};
+
+struct io_cqring_offsets {
+	__u32 head;
+	__u32 tail;
+	__u32 ring_mask;
+	__u32 ring_entries;
+	__u32 overflow;
+	__u32 cqes;
+	__u32 resv[4];
+};
+
+/*
+ * io_uring_enter(2) flags
+ */
+#define IORING_ENTER_GETEVENTS	(1 << 0)
+
+/*
+ * Passed in for io_uring_setup(2). Copied back with updated info on success
+ */
+struct io_uring_params {
+	__u32 sq_entries;
+	__u32 cq_entries;
+	__u32 flags;
+	__u16 resv[10];
+	struct io_sqring_offsets sq_off;
+	struct io_cqring_offsets cq_off;
+};
+
+#endif
diff --git a/init/Kconfig b/init/Kconfig
index 513fa544a134..0cf723867e69 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1403,6 +1403,15 @@ config AIO
 	  by some high performance threaded applications. Disabling
 	  this option saves about 7k.
 
+config IO_URING
+	bool "Enable IO uring support" if EXPERT
+	select ANON_INODES
+	default y
+	help
+	  This option enables support for the io_uring interface, enabling
+	  applications to submit and completion IO through submission and
+	  completion rings that are shared between the kernel and application.
+
 config ADVISE_SYSCALLS
 	bool "Enable madvise/fadvise syscalls" if EXPERT
 	default y
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index ab9d0e3c6d50..d754811ec780 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -46,6 +46,9 @@ COND_SYSCALL(io_getevents);
 COND_SYSCALL(io_pgetevents);
 COND_SYSCALL_COMPAT(io_getevents);
 COND_SYSCALL_COMPAT(io_pgetevents);
+COND_SYSCALL(io_uring_setup);
+COND_SYSCALL_COMPAT(io_uring_setup);
+COND_SYSCALL(io_uring_enter);
 
 /* fs/xattr.c */
 
-- 
2.17.1

Re: [PATCH 05/18] Add io_uring IO interface

[Christoph Hellwig]

[please make sure linux-api and linux-man are CCed on new syscalls
so that we get API experts to review them]

> io_uring_enter(fd, to_submit, min_complete, flags)
> 	Initiates IO against the rings mapped to this fd, or waits for
> 	them to complete, or both. The behavior is controlled by the
> 	parameters passed in. If 'to_submit' is non-zero, then we'll
> 	try and submit new IO. If IORING_ENTER_GETEVENTS is set, the
> 	kernel will wait for 'min_complete' events, if they aren't
> 	already available. It's valid to set IORING_ENTER_GETEVENTS
> 	and 'min_complete' == 0 at the same time, this allows the
> 	kernel to return already completed events without waiting
> 	for them. This is useful only for polling, as for IRQ
> 	driven IO, the application can just check the CQ ring
> 	without entering the kernel.

Especially with poll support now in the series, don't we need a ѕigmask
argument similar to pselect/ppoll/io_pgetevents now to deal with signal
blocking during waiting for events?

> +struct sqe_submit {
> +	const struct io_uring_sqe *sqe;
> +	unsigned index;
> +};

Can you make sure all the structs use tab indentation for their
field names?  Maybe even the same for all structs just to be nice
to my eyes?

> +static int io_import_iovec(struct io_ring_ctx *ctx, int rw,
> +			   const struct io_uring_sqe *sqe,
> +			   struct iovec **iovec, struct iov_iter *iter)
> +{
> +	void __user *buf = u64_to_user_ptr(sqe->addr);
> +
> +#ifdef CONFIG_COMPAT
> +	if (ctx->compat)
> +		return compat_import_iovec(rw, buf, sqe->len, UIO_FASTIOV,
> +						iovec, iter);
> +#endif

I think we can just check in_compat_syscall() here, which means we
can kill the ->compat member, and the separate compat version of the
setup syscall.

> +/*
> + * IORING_OP_NOP just posts a completion event, nothing else.
> + */
> +static int io_nop(struct io_kiocb *req, const struct io_uring_sqe *sqe)
> +{
> +	struct io_ring_ctx *ctx = req->ctx;
> +
> +	__io_cqring_add_event(ctx, sqe->user_data, 0, 0);

Can you explain why not taking the completion lock is safe here?  And
why we want to have such a somewhat dangerous special case just for the
no-op benchmarking aid?

> +static bool io_get_sqring(struct io_ring_ctx *ctx, struct sqe_submit *s)
> +{
> +	struct io_sq_ring *ring = ctx->sq_ring;
> +	unsigned head;
> +
> +	head = ctx->cached_sq_head;
> +	smp_rmb();
> +	if (head == READ_ONCE(ring->r.tail))
> +		return false;

Do we really need to optimize the sq_head == tail case so much? Or
am I missing why we are using the cached sq head case here?  Maybe
add some more comments for a start.

> +static int __io_uring_enter(struct io_ring_ctx *ctx, unsigned to_submit,
> +			    unsigned min_complete, unsigned flags)
> +{
> +	int ret = 0;
> +
> +	if (to_submit) {
> +		ret = io_ring_submit(ctx, to_submit);
> +		if (ret < 0)
> +			return ret;
> +	}
> +	if (flags & IORING_ENTER_GETEVENTS) {
> +		int get_ret;
> +
> +		if (!ret && to_submit)
> +			min_complete = 0;

Why do we have this special case?  Does it need some documentation?

> +
> +		get_ret = io_cqring_wait(ctx, min_complete);
> +		if (get_ret < 0 && !ret)
> +			ret = get_ret;
> +	}
> +
> +	return ret;

Maybe using different names and slightly different semantics for the
return values would clear some of this up?

	if (to_submit) {
		submitted = io_ring_submit(ctx, to_submit);
		if (submitted < 0)
			return submitted;
	}
	if (flags & IORING_ENTER_GETEVENTS) {
		...
		ret = io_cqring_wait(ctx, min_complete);
	}

	return submitted ? submitted : ret;

> +static int io_sq_offload_start(struct io_ring_ctx *ctx)

> +static void io_sq_offload_stop(struct io_ring_ctx *ctx)

Can we just merge these two functions into the callers?  Currently
the flow is a little odd with these helpers that don't seem to be
too clear about their responsibilities.

> +static void io_free_scq_urings(struct io_ring_ctx *ctx)
> +{
> +	if (ctx->sq_ring) {
> +		page_frag_free(ctx->sq_ring);
> +		ctx->sq_ring = NULL;
> +	}
> +	if (ctx->sq_sqes) {
> +		page_frag_free(ctx->sq_sqes);
> +		ctx->sq_sqes = NULL;
> +	}
> +	if (ctx->cq_ring) {
> +		page_frag_free(ctx->cq_ring);
> +		ctx->cq_ring = NULL;
> +	}

Why is this using the page_frag helpers?  Also the callers just free
these ctx structure, so there isn't much of a point zeroing them out.

Also I'd be tempted to open code the freeing in io_allocate_scq_urings
instead of caling the helper, which would avoid the NULL checks and
make the error handling code a little more obvious.

> +	if (mutex_trylock(&ctx->uring_lock)) {
> +		ret = __io_uring_enter(ctx, to_submit, min_complete, flags);

do we even need the separate __io_uring_enter helper?

> +static void io_fill_offsets(struct io_uring_params *p)

Do we really need this as a separate helper?

Re: [PATCH 05/18] Add io_uring IO interface

[Jens Axboe]

On 1/28/19 7:57 AM, Christoph Hellwig wrote:
> [please make sure linux-api and linux-man are CCed on new syscalls
> so that we get API experts to review them]

I already did review with Arnd on those parts, I'll add linux-api and
linux-man for the next posting.

>> io_uring_enter(fd, to_submit, min_complete, flags)
>> 	Initiates IO against the rings mapped to this fd, or waits for
>> 	them to complete, or both. The behavior is controlled by the
>> 	parameters passed in. If 'to_submit' is non-zero, then we'll
>> 	try and submit new IO. If IORING_ENTER_GETEVENTS is set, the
>> 	kernel will wait for 'min_complete' events, if they aren't
>> 	already available. It's valid to set IORING_ENTER_GETEVENTS
>> 	and 'min_complete' == 0 at the same time, this allows the
>> 	kernel to return already completed events without waiting
>> 	for them. This is useful only for polling, as for IRQ
>> 	driven IO, the application can just check the CQ ring
>> 	without entering the kernel.
> 
> Especially with poll support now in the series, don't we need a ѕigmask
> argument similar to pselect/ppoll/io_pgetevents now to deal with signal
> blocking during waiting for events?

I guess we do.

>> +struct sqe_submit {
>> +	const struct io_uring_sqe *sqe;
>> +	unsigned index;
>> +};
> 
> Can you make sure all the structs use tab indentation for their
> field names?  Maybe even the same for all structs just to be nice
> to my eyes?

Sure, fixed.

>> +static int io_import_iovec(struct io_ring_ctx *ctx, int rw,
>> +			   const struct io_uring_sqe *sqe,
>> +			   struct iovec **iovec, struct iov_iter *iter)
>> +{
>> +	void __user *buf = u64_to_user_ptr(sqe->addr);
>> +
>> +#ifdef CONFIG_COMPAT
>> +	if (ctx->compat)
>> +		return compat_import_iovec(rw, buf, sqe->len, UIO_FASTIOV,
>> +						iovec, iter);
>> +#endif
> 
> I think we can just check in_compat_syscall() here, which means we
> can kill the ->compat member, and the separate compat version of the
> setup syscall.

Good point, I'll switch to using that so we don't have to track it.

>> +/*
>> + * IORING_OP_NOP just posts a completion event, nothing else.
>> + */
>> +static int io_nop(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>> +{
>> +	struct io_ring_ctx *ctx = req->ctx;
>> +
>> +	__io_cqring_add_event(ctx, sqe->user_data, 0, 0);
> 
> Can you explain why not taking the completion lock is safe here?  And
> why we want to have such a somewhat dangerous special case just for the
> no-op benchmarking aid?

Was going to say it's safe because we always fill the ring inside the
ring mutex, but that won't work if we intermingle with non-polled IO.
I'll switch it to using the normal locked variant.

>> +static bool io_get_sqring(struct io_ring_ctx *ctx, struct sqe_submit *s)
>> +{
>> +	struct io_sq_ring *ring = ctx->sq_ring;
>> +	unsigned head;
>> +
>> +	head = ctx->cached_sq_head;
>> +	smp_rmb();
>> +	if (head == READ_ONCE(ring->r.tail))
>> +		return false;
> 
> Do we really need to optimize the sq_head == tail case so much? Or
> am I missing why we are using the cached sq head case here?  Maybe
> add some more comments for a start.

It basically serves two purposes:

1) When we grab multiple events, only have to update the actual ring
   tail once. This is a big deal, especially on archs where the barriers
   are more expensive.

2) It means the kernel tracks the sq tail and cq head, instead of
   completely relying on the application. This seems a much saner
   choice.

>> +static int __io_uring_enter(struct io_ring_ctx *ctx, unsigned to_submit,
>> +			    unsigned min_complete, unsigned flags)
>> +{
>> +	int ret = 0;
>> +
>> +	if (to_submit) {
>> +		ret = io_ring_submit(ctx, to_submit);
>> +		if (ret < 0)
>> +			return ret;
>> +	}
>> +	if (flags & IORING_ENTER_GETEVENTS) {
>> +		int get_ret;
>> +
>> +		if (!ret && to_submit)
>> +			min_complete = 0;
> 
> Why do we have this special case?  Does it need some documentation?

At least for polled IO, if we don't submit what we were asked to, then
we can't reliably poll for the passed in number of events. The
min_complete from the application could very well include the
expectation that to_submit were submitted as well.

I'll add a comment.

>> +
>> +		get_ret = io_cqring_wait(ctx, min_complete);
>> +		if (get_ret < 0 && !ret)
>> +			ret = get_ret;
>> +	}
>> +
>> +	return ret;
> 
> Maybe using different names and slightly different semantics for the
> return values would clear some of this up?
> 
> 	if (to_submit) {
> 		submitted = io_ring_submit(ctx, to_submit);
> 		if (submitted < 0)
> 			return submitted;
> 	}
> 	if (flags & IORING_ENTER_GETEVENTS) {
> 		...
> 		ret = io_cqring_wait(ctx, min_complete);
> 	}
> 
> 	return submitted ? submitted : ret;

That would probably make it more readable, I'll make this change.

>> +static int io_sq_offload_start(struct io_ring_ctx *ctx)
> 
>> +static void io_sq_offload_stop(struct io_ring_ctx *ctx)
> 
> Can we just merge these two functions into the callers?  Currently
> the flow is a little odd with these helpers that don't seem to be
> too clear about their responsibilities.

In the initial patch I agree, but with the later thread addition, I like
having it in a separate helper. At least for the start, the top side is
more trivial.

>> +static void io_free_scq_urings(struct io_ring_ctx *ctx)
>> +{
>> +	if (ctx->sq_ring) {
>> +		page_frag_free(ctx->sq_ring);
>> +		ctx->sq_ring = NULL;
>> +	}
>> +	if (ctx->sq_sqes) {
>> +		page_frag_free(ctx->sq_sqes);
>> +		ctx->sq_sqes = NULL;
>> +	}
>> +	if (ctx->cq_ring) {
>> +		page_frag_free(ctx->cq_ring);
>> +		ctx->cq_ring = NULL;
>> +	}
> 
> Why is this using the page_frag helpers?  Also the callers just free
> these ctx structure, so there isn't much of a point zeroing them out.

Why not use the page frag helpers? No point in open-coding it. I can
kill the zeroing, double call would be a bug anyway.

> Also I'd be tempted to open code the freeing in io_allocate_scq_urings
> instead of caling the helper, which would avoid the NULL checks and
> make the error handling code a little more obvious.

OK

>> +	if (mutex_trylock(&ctx->uring_lock)) {
>> +		ret = __io_uring_enter(ctx, to_submit, min_complete, flags);
> 
> do we even need the separate __io_uring_enter helper?

I like having it nicely separated.

>> +static void io_fill_offsets(struct io_uring_params *p)
> 
> Do we really need this as a separate helper?

That does seem pointless, folded in.

-- 
Jens Axboe

Re: [PATCH 05/18] Add io_uring IO interface

[Christoph Hellwig]

On Mon, Jan 28, 2019 at 09:26:42AM -0700, Jens Axboe wrote:
> >> +static void io_free_scq_urings(struct io_ring_ctx *ctx)
> >> +{
> >> +	if (ctx->sq_ring) {
> >> +		page_frag_free(ctx->sq_ring);
> >> +		ctx->sq_ring = NULL;
> >> +	}
> >> +	if (ctx->sq_sqes) {
> >> +		page_frag_free(ctx->sq_sqes);
> >> +		ctx->sq_sqes = NULL;
> >> +	}
> >> +	if (ctx->cq_ring) {
> >> +		page_frag_free(ctx->cq_ring);
> >> +		ctx->cq_ring = NULL;
> >> +	}
> > 
> > Why is this using the page_frag helpers?  Also the callers just free
> > these ctx structure, so there isn't much of a point zeroing them out.
> 
> Why not use the page frag helpers? No point in open-coding it. I can
> kill the zeroing, double call would be a bug anyway.

Because they are at a different level of abstraction, and someone
might change the implementation, and is unlikely to catch the io_uring
mix of interfaces.  If you think this is really useful we should also
export the helpers under a different name and with documentation.
(and add a __get_free_pages version that returns a pointer..)

Re: [PATCH 05/18] Add io_uring IO interface

[Jens Axboe]

On 1/28/19 9:34 AM, Christoph Hellwig wrote:
> On Mon, Jan 28, 2019 at 09:26:42AM -0700, Jens Axboe wrote:
>>>> +static void io_free_scq_urings(struct io_ring_ctx *ctx)
>>>> +{
>>>> +	if (ctx->sq_ring) {
>>>> +		page_frag_free(ctx->sq_ring);
>>>> +		ctx->sq_ring = NULL;
>>>> +	}
>>>> +	if (ctx->sq_sqes) {
>>>> +		page_frag_free(ctx->sq_sqes);
>>>> +		ctx->sq_sqes = NULL;
>>>> +	}
>>>> +	if (ctx->cq_ring) {
>>>> +		page_frag_free(ctx->cq_ring);
>>>> +		ctx->cq_ring = NULL;
>>>> +	}
>>>
>>> Why is this using the page_frag helpers?  Also the callers just free
>>> these ctx structure, so there isn't much of a point zeroing them out.
>>
>> Why not use the page frag helpers? No point in open-coding it. I can
>> kill the zeroing, double call would be a bug anyway.
> 
> Because they are at a different level of abstraction, and someone
> might change the implementation, and is unlikely to catch the io_uring
> mix of interfaces.  If you think this is really useful we should also
> export the helpers under a different name and with documentation.
> (and add a __get_free_pages version that returns a pointer..)

Fair enough, I'll avoid using the page_frag_free().

-- 
Jens Axboe

Re: [PATCH 05/18] Add io_uring IO interface

[Jens Axboe]

On 1/28/19 7:57 AM, Christoph Hellwig wrote:
> [please make sure linux-api and linux-man are CCed on new syscalls
> so that we get API experts to review them]
> 
>> io_uring_enter(fd, to_submit, min_complete, flags)
>> 	Initiates IO against the rings mapped to this fd, or waits for
>> 	them to complete, or both. The behavior is controlled by the
>> 	parameters passed in. If 'to_submit' is non-zero, then we'll
>> 	try and submit new IO. If IORING_ENTER_GETEVENTS is set, the
>> 	kernel will wait for 'min_complete' events, if they aren't
>> 	already available. It's valid to set IORING_ENTER_GETEVENTS
>> 	and 'min_complete' == 0 at the same time, this allows the
>> 	kernel to return already completed events without waiting
>> 	for them. This is useful only for polling, as for IRQ
>> 	driven IO, the application can just check the CQ ring
>> 	without entering the kernel.
> 
> Especially with poll support now in the series, don't we need a ѕigmask
> argument similar to pselect/ppoll/io_pgetevents now to deal with signal
> blocking during waiting for events?

Is there any way to avoid passing in the sigset_t size? If it's just a
32-bit/64-bit thing, surely the in_compat_syscall() could cover it? Or
are there other cases that need to be catered to?

-- 
Jens Axboe

Re: [PATCH 05/18] Add io_uring IO interface

[Christoph Hellwig]

On Mon, Jan 28, 2019 at 11:25:12AM -0700, Jens Axboe wrote:
> > Especially with poll support now in the series, don't we need a ѕigmask
> > argument similar to pselect/ppoll/io_pgetevents now to deal with signal
> > blocking during waiting for events?
> 
> Is there any way to avoid passing in the sigset_t size? If it's just a
> 32-bit/64-bit thing, surely the in_compat_syscall() could cover it? Or
> are there other cases that need to be catered to?

As far as I can tell we never look at it, never looked at it and don't
have any plans to look at it anytime soon.  But when I tried to omit
it for io_pgetevents I got stong pushback and thus had to add the
crazy double indirection calling convention.

Re: [PATCH 05/18] Add io_uring IO interface

[Arnd Bergmann]

On Tue, Jan 29, 2019 at 7:30 AM Christoph Hellwig <hch@lst.de> wrote:
>
> On Mon, Jan 28, 2019 at 11:25:12AM -0700, Jens Axboe wrote:
> > > Especially with poll support now in the series, don't we need a ѕigmask
> > > argument similar to pselect/ppoll/io_pgetevents now to deal with signal
> > > blocking during waiting for events?
> >
> > Is there any way to avoid passing in the sigset_t size? If it's just a
> > 32-bit/64-bit thing, surely the in_compat_syscall() could cover it? Or
> > are there other cases that need to be catered to?
>
> As far as I can tell we never look at it, never looked at it and don't
> have any plans to look at it anytime soon.  But when I tried to omit
> it for io_pgetevents I got stong pushback and thus had to add the
> crazy double indirection calling convention.

Deepa has recently reworked the handling for the sigset_t handling
to be more consistent. As I understand it, we only ever check the
size argument to ensure that user and kernel space agree on
the size, as it there had been some historic differences.

If you pass a signal mask to a syscall, you should now just use the
set_user_sigmask()/set_compat_user_sigmask()/restore_user_sigmask()
helpers. The compat version is required for the incompatible bit order
between 32-bit and 64-bit big-endian architectures (on little-endian, compat
and native signal masks are compatible), and to deal with the one
architecture that has an _NSIG defined to something other than 64:
MIPS uses 128 because of a historic accident.

I think Deepa originally suggested combining set_user_sigmask()
and set_compat_user_sigmask(), using an in_compat_syscall()
check. This would let us simplify a number of compat syscalls
(ppoll, ppoll_time32, pselect6, pselect6_time32, epoll_pwait()
io_pgetevents_time64, io_pgetevents_time32). I advised against
changing it at the time for consistency with other compat syscalls,
but it's something we can still do now.

There was a recent discussion about the size of sigset_t in glibc,
which is 1024 bits there instead of 64 bits in the kernel, the idea
being that the kernel might eventually grow more signals at
some point in the future, as we did when we extended from 32
to 64 a long time ago with the addition of the rt_sig* signals;
see the thread around
https://www.spinics.net/lists/linux-snps-arc/msg04860.html

    Arnd

Re: [PATCH 05/18] Add io_uring IO interface

[Jens Axboe]

On 1/29/19 4:58 AM, Arnd Bergmann wrote:
> On Tue, Jan 29, 2019 at 7:30 AM Christoph Hellwig <hch@lst.de> wrote:
>>
>> On Mon, Jan 28, 2019 at 11:25:12AM -0700, Jens Axboe wrote:
>>>> Especially with poll support now in the series, don't we need a ѕigmask
>>>> argument similar to pselect/ppoll/io_pgetevents now to deal with signal
>>>> blocking during waiting for events?
>>>
>>> Is there any way to avoid passing in the sigset_t size? If it's just a
>>> 32-bit/64-bit thing, surely the in_compat_syscall() could cover it? Or
>>> are there other cases that need to be catered to?
>>
>> As far as I can tell we never look at it, never looked at it and don't
>> have any plans to look at it anytime soon.  But when I tried to omit
>> it for io_pgetevents I got stong pushback and thus had to add the
>> crazy double indirection calling convention.
> 
> Deepa has recently reworked the handling for the sigset_t handling
> to be more consistent. As I understand it, we only ever check the
> size argument to ensure that user and kernel space agree on
> the size, as it there had been some historic differences.
> 
> If you pass a signal mask to a syscall, you should now just use the
> set_user_sigmask()/set_compat_user_sigmask()/restore_user_sigmask()
> helpers. The compat version is required for the incompatible bit order
> between 32-bit and 64-bit big-endian architectures (on little-endian, compat
> and native signal masks are compatible), and to deal with the one
> architecture that has an _NSIG defined to something other than 64:
> MIPS uses 128 because of a historic accident.
> 
> I think Deepa originally suggested combining set_user_sigmask()
> and set_compat_user_sigmask(), using an in_compat_syscall()
> check. This would let us simplify a number of compat syscalls
> (ppoll, ppoll_time32, pselect6, pselect6_time32, epoll_pwait()
> io_pgetevents_time64, io_pgetevents_time32). I advised against
> changing it at the time for consistency with other compat syscalls,
> but it's something we can still do now.

That's good info. I am currently using set_user_sigmask() for it.
I'd really like to avoid having to pass in a sigset_t size for the
system call, however. What's the best way of achieving that? Can I get
away with doing something like this:

	if (in_compat_syscall()) {
		const compat_sigset_t __user *compat_sig;

		compat_sig = (const compat_sigset_t __user *) sig;
		ret = set_compat_user_sigmask(compat_sig, &ksigmask,
						&sigsaved, _NSIG_WORDS);
	} else {
		ret = set_user_sigmask(sig, &ksigmask, &sigsaved,
						_NSIG_WORDS);
	}

-- 
Jens Axboe

Re: [PATCH 05/18] Add io_uring IO interface

[Arnd Bergmann]

On Tue, Jan 29, 2019 at 4:20 PM Jens Axboe <axboe@kernel.dk> wrote:
> On 1/29/19 4:58 AM, Arnd Bergmann wrote:
> > On Tue, Jan 29, 2019 at 7:30 AM Christoph Hellwig <hch@lst.de> wrote:
> >>> On Mon, Jan 28, 2019 at 11:25:12AM -0700, Jens Axboe wrote:
> >>>> Especially with poll support now in the series, don't we need a ѕigmask
> >>>> argument similar to pselect/ppoll/io_pgetevents now to deal with signal
> >>>> blocking during waiting for events?
> >>>
> >>> Is there any way to avoid passing in the sigset_t size? If it's just a
> >>> 32-bit/64-bit thing, surely the in_compat_syscall() could cover it? Or
> >>> are there other cases that need to be catered to?
> >>
> >> As far as I can tell we never look at it, never looked at it and don't
> >> have any plans to look at it anytime soon.  But when I tried to omit
> >> it for io_pgetevents I got stong pushback and thus had to add the
> >> crazy double indirection calling convention.
>
> That's good info. I am currently using set_user_sigmask() for it.
> I'd really like to avoid having to pass in a sigset_t size for the
> system call, however.

I really wouldn't do it, given that all other signal handling interfaces
are prepared for longer signal masks. You /could/ probably extend
it later with a flags bit to signify a longer mask instead of using
the entire register to hold the bit length, it just seems really
inconsistent with all other system calls.

      Arnd




> What's the best way of achieving that? Can I get
> away with doing something like this:
>
>         if (in_compat_syscall()) {
>                 const compat_sigset_t __user *compat_sig;
>
>                 compat_sig = (const compat_sigset_t __user *) sig;
>                 ret = set_compat_user_sigmask(compat_sig, &ksigmask,
>                                                 &sigsaved, _NSIG_WORDS);
>         } else {
>                 ret = set_user_sigmask(sig, &ksigmask, &sigsaved,
>                                                 _NSIG_WORDS);
>         }

Re: [PATCH 05/18] Add io_uring IO interface

[Jens Axboe]

On 1/29/19 9:18 AM, Arnd Bergmann wrote:
> On Tue, Jan 29, 2019 at 4:20 PM Jens Axboe <axboe@kernel.dk> wrote:
>> On 1/29/19 4:58 AM, Arnd Bergmann wrote:
>>> On Tue, Jan 29, 2019 at 7:30 AM Christoph Hellwig <hch@lst.de> wrote:
>>>>> On Mon, Jan 28, 2019 at 11:25:12AM -0700, Jens Axboe wrote:
>>>>>> Especially with poll support now in the series, don't we need a ѕigmask
>>>>>> argument similar to pselect/ppoll/io_pgetevents now to deal with signal
>>>>>> blocking during waiting for events?
>>>>>
>>>>> Is there any way to avoid passing in the sigset_t size? If it's just a
>>>>> 32-bit/64-bit thing, surely the in_compat_syscall() could cover it? Or
>>>>> are there other cases that need to be catered to?
>>>>
>>>> As far as I can tell we never look at it, never looked at it and don't
>>>> have any plans to look at it anytime soon.  But when I tried to omit
>>>> it for io_pgetevents I got stong pushback and thus had to add the
>>>> crazy double indirection calling convention.
>>
>> That's good info. I am currently using set_user_sigmask() for it.
>> I'd really like to avoid having to pass in a sigset_t size for the
>> system call, however.
> 
> I really wouldn't do it, given that all other signal handling interfaces
> are prepared for longer signal masks. You /could/ probably extend
> it later with a flags bit to signify a longer mask instead of using
> the entire register to hold the bit length, it just seems really
> inconsistent with all other system calls.

Damnit! OK, I'll keep what I currently have then.

-- 
Jens Axboe

Re: [PATCH 05/18] Add io_uring IO interface

[Arnd Bergmann]

On Tue, Jan 29, 2019 at 5:19 PM Jens Axboe <axboe@kernel.dk> wrote:
> On 1/29/19 9:18 AM, Arnd Bergmann wrote:
> > On Tue, Jan 29, 2019 at 4:20 PM Jens Axboe <axboe@kernel.dk> wrote:
> >> That's good info. I am currently using set_user_sigmask() for it.
> >> I'd really like to avoid having to pass in a sigset_t size for the
> >> system call, however.
> >
> > I really wouldn't do it, given that all other signal handling interfaces
> > are prepared for longer signal masks. You /could/ probably extend
> > it later with a flags bit to signify a longer mask instead of using
> > the entire register to hold the bit length, it just seems really
> > inconsistent with all other system calls.
>
> Damnit! OK, I'll keep what I currently have then.

As long as you stay within the 6-argument syscall contraints,
the cost of passing the length is basically free, right?

Is there anything else you are worried about?

     Arnd

Re: [PATCH 05/18] Add io_uring IO interface

[Jens Axboe]

On 1/29/19 9:26 AM, Arnd Bergmann wrote:
> On Tue, Jan 29, 2019 at 5:19 PM Jens Axboe <axboe@kernel.dk> wrote:
>> On 1/29/19 9:18 AM, Arnd Bergmann wrote:
>>> On Tue, Jan 29, 2019 at 4:20 PM Jens Axboe <axboe@kernel.dk> wrote:
>>>> That's good info. I am currently using set_user_sigmask() for it.
>>>> I'd really like to avoid having to pass in a sigset_t size for the
>>>> system call, however.
>>>
>>> I really wouldn't do it, given that all other signal handling interfaces
>>> are prepared for longer signal masks. You /could/ probably extend
>>> it later with a flags bit to signify a longer mask instead of using
>>> the entire register to hold the bit length, it just seems really
>>> inconsistent with all other system calls.
>>
>> Damnit! OK, I'll keep what I currently have then.
> 
> As long as you stay within the 6-argument syscall contraints,
> the cost of passing the length is basically free, right?
> 
> Is there anything else you are worried about?

My main worry is not the extra argument, more that we're at capacity
for the system call. If we wanted to add a timeout parameter, then we'd
need to bundle them up, which sucks.

But I think we're fine, I'll go with what I have.

-- 
Jens Axboe

Re: [PATCH 05/18] Add io_uring IO interface

[Arnd Bergmann]

On Tue, Jan 29, 2019 at 5:28 PM Jens Axboe <axboe@kernel.dk> wrote:
>
> On 1/29/19 9:26 AM, Arnd Bergmann wrote:
> > On Tue, Jan 29, 2019 at 5:19 PM Jens Axboe <axboe@kernel.dk> wrote:
> >> On 1/29/19 9:18 AM, Arnd Bergmann wrote:
> >>> On Tue, Jan 29, 2019 at 4:20 PM Jens Axboe <axboe@kernel.dk> wrote:
> >>>> That's good info. I am currently using set_user_sigmask() for it.
> >>>> I'd really like to avoid having to pass in a sigset_t size for the
> >>>> system call, however.
> >>>
> >>> I really wouldn't do it, given that all other signal handling interfaces
> >>> are prepared for longer signal masks. You /could/ probably extend
> >>> it later with a flags bit to signify a longer mask instead of using
> >>> the entire register to hold the bit length, it just seems really
> >>> inconsistent with all other system calls.
> >>
> >> Damnit! OK, I'll keep what I currently have then.
> >
> > As long as you stay within the 6-argument syscall contraints,
> > the cost of passing the length is basically free, right?
> >
> > Is there anything else you are worried about?
>
> My main worry is not the extra argument, more that we're at capacity
> for the system call. If we wanted to add a timeout parameter, then we'd
> need to bundle them up, which sucks.

Ok, got it. If it turns out that we do need the timeout argument after all,
you could avoid one indirection level by grouping the sigset_t with
min_complete, timeout_ns and/or sigset_size, as long as the
sigset_t comes last (similar to struct sigaction).

Another (also awkward) trick might be to combine min_complete and
sigset_size into a 32-bit integer argument, as each of them can
fit into 16 bits.

      Arnd

Re: [PATCH 05/18] Add io_uring IO interface

[Andy Lutomirski]

On Mon, Jan 28, 2019 at 6:57 AM Christoph Hellwig <hch@lst.de> wrote:
>
> [please make sure linux-api and linux-man are CCed on new syscalls
> so that we get API experts to review them]

> > +static int io_import_iovec(struct io_ring_ctx *ctx, int rw,
> > +                        const struct io_uring_sqe *sqe,
> > +                        struct iovec **iovec, struct iov_iter *iter)
> > +{
> > +     void __user *buf = u64_to_user_ptr(sqe->addr);
> > +
> > +#ifdef CONFIG_COMPAT
> > +     if (ctx->compat)
> > +             return compat_import_iovec(rw, buf, sqe->len, UIO_FASTIOV,
> > +                                             iovec, iter);
> > +#endif
>
> I think we can just check in_compat_syscall() here, which means we
> can kill the ->compat member, and the separate compat version of the
> setup syscall.
>

Since this whole API is new, I don't suppose you could introduce a
struct iovec64 or similar and just make the ABI be identical for
64-bit and 32-bit code?

--Andy

Re: [PATCH 05/18] Add io_uring IO interface

[Jens Axboe]

On 1/28/19 5:47 PM, Andy Lutomirski wrote:
> On Mon, Jan 28, 2019 at 6:57 AM Christoph Hellwig <hch@lst.de> wrote:
>>
>> [please make sure linux-api and linux-man are CCed on new syscalls
>> so that we get API experts to review them]
> 
>>> +static int io_import_iovec(struct io_ring_ctx *ctx, int rw,
>>> +                        const struct io_uring_sqe *sqe,
>>> +                        struct iovec **iovec, struct iov_iter *iter)
>>> +{
>>> +     void __user *buf = u64_to_user_ptr(sqe->addr);
>>> +
>>> +#ifdef CONFIG_COMPAT
>>> +     if (ctx->compat)
>>> +             return compat_import_iovec(rw, buf, sqe->len, UIO_FASTIOV,
>>> +                                             iovec, iter);
>>> +#endif
>>
>> I think we can just check in_compat_syscall() here, which means we
>> can kill the ->compat member, and the separate compat version of the
>> setup syscall.
>>
> 
> Since this whole API is new, I don't suppose you could introduce a
> struct iovec64 or similar and just make the ABI be identical for
> 64-bit and 32-bit code?

Sure, that would be straight forward. Is there a strong reason to do
so outside of "that would be nice"? It's not like it's a huge amount
of code.

-- 
Jens Axboe

Re: [PATCH 05/18] Add io_uring IO interface

[Christoph Hellwig]

On Mon, Jan 28, 2019 at 06:20:08PM -0700, Jens Axboe wrote:
> Sure, that would be straight forward. Is there a strong reason to do
> so outside of "that would be nice"? It's not like it's a huge amount
> of code.

And it would be really painful for userspace.  Because now you
can't pass struct iovec through from a higher level, but will instead
of to copy the iovec to a different type in the submission path.

Re: [PATCH 05/18] Add io_uring IO interface

[Arnd Bergmann]

On Tue, Jan 29, 2019 at 7:45 AM Christoph Hellwig <hch@lst.de> wrote:
>
> On Mon, Jan 28, 2019 at 06:20:08PM -0700, Jens Axboe wrote:
> > Sure, that would be straight forward. Is there a strong reason to do
> > so outside of "that would be nice"? It's not like it's a huge amount
> > of code.
>
> And it would be really painful for userspace.  Because now you
> can't pass struct iovec through from a higher level, but will instead
> of to copy the iovec to a different type in the submission path.

Agreed. However, if we decide to add the in_compat_syscall() check
to set_user_sigmask()/set_compat_user_sigmask(), we probably want
to do the same thing in import_iovec()/compat_import_iovec() and
rw_copy_check_uvector()/compat_rw_copy_check_uvector().

      Arnd

Re: [PATCH 05/18] Add io_uring IO interface

[Andy Lutomirski]

>>> On Jan 28, 2019, at 5:20 PM, Jens Axboe <axboe@kernel.dk> wrote:
>>>
>>> On 1/28/19 5:47 PM, Andy Lutomirski wrote:
>>> On Mon, Jan 28, 2019 at 6:57 AM Christoph Hellwig <hch@lst.de> wrote:
>>>
>>> [please make sure linux-api and linux-man are CCed on new syscalls
>>> so that we get API experts to review them]
>>
>>>> +static int io_import_iovec(struct io_ring_ctx *ctx, int rw,
>>>> +                        const struct io_uring_sqe *sqe,
>>>> +                        struct iovec **iovec, struct iov_iter *iter)
>>>> +{
>>>> +     void __user *buf = u64_to_user_ptr(sqe->addr);
>>>> +
>>>> +#ifdef CONFIG_COMPAT
>>>> +     if (ctx->compat)
>>>> +             return compat_import_iovec(rw, buf, sqe->len, UIO_FASTIOV,
>>>> +                                             iovec, iter);
>>>> +#endif
>>>
>>> I think we can just check in_compat_syscall() here, which means we
>>> can kill the ->compat member, and the separate compat version of the
>>> setup syscall.
>>
>> Since this whole API is new, I don't suppose you could introduce a
>> struct iovec64 or similar and just make the ABI be identical for
>> 64-bit and 32-bit code?
>
> Sure, that would be straight forward. Is there a strong reason to do
> so outside of "that would be nice"? It's not like it's a huge amount
> of code.

Here are some minor-ish benefits:

 - It avoids having a code path that is only used with 32 bit code on
64 bit kernels and is therefore rarely tested.  (In this particular
case, the code path doesn't diverge much, but for most compat
syscalls, it's almost an entirely separate implementation of the main
syscall code.)

 - It makes life easier for tools like strace.

 - It minimizes the chance of making a giant mess on x32, which isn't
really native or compat.

--Andy

Re: [PATCH 05/18] Add io_uring IO interface

[Jens Axboe]

On 1/30/19 10:11 PM, Andy Lutomirski wrote:
>>>> On Jan 28, 2019, at 5:20 PM, Jens Axboe <axboe@kernel.dk> wrote:
>>>>
>>>> On 1/28/19 5:47 PM, Andy Lutomirski wrote:
>>>> On Mon, Jan 28, 2019 at 6:57 AM Christoph Hellwig <hch@lst.de> wrote:
>>>>
>>>> [please make sure linux-api and linux-man are CCed on new syscalls
>>>> so that we get API experts to review them]
>>>
>>>>> +static int io_import_iovec(struct io_ring_ctx *ctx, int rw,
>>>>> +                        const struct io_uring_sqe *sqe,
>>>>> +                        struct iovec **iovec, struct iov_iter *iter)
>>>>> +{
>>>>> +     void __user *buf = u64_to_user_ptr(sqe->addr);
>>>>> +
>>>>> +#ifdef CONFIG_COMPAT
>>>>> +     if (ctx->compat)
>>>>> +             return compat_import_iovec(rw, buf, sqe->len, UIO_FASTIOV,
>>>>> +                                             iovec, iter);
>>>>> +#endif
>>>>
>>>> I think we can just check in_compat_syscall() here, which means we
>>>> can kill the ->compat member, and the separate compat version of the
>>>> setup syscall.
>>>
>>> Since this whole API is new, I don't suppose you could introduce a
>>> struct iovec64 or similar and just make the ABI be identical for
>>> 64-bit and 32-bit code?
>>
>> Sure, that would be straight forward. Is there a strong reason to do
>> so outside of "that would be nice"? It's not like it's a huge amount
>> of code.
> 
> Here are some minor-ish benefits:
> 
>  - It avoids having a code path that is only used with 32 bit code on
> 64 bit kernels and is therefore rarely tested.  (In this particular
> case, the code path doesn't diverge much, but for most compat
> syscalls, it's almost an entirely separate implementation of the main
> syscall code.)
> 
>  - It makes life easier for tools like strace.
> 
>  - It minimizes the chance of making a giant mess on x32, which isn't
> really native or compat.

Not really anything major here, at least not to the extent that
suffering the pain of having a different iovec for this is warranted.

-- 
Jens Axboe

[PATCH 06/18] io_uring: add fsync support

[Jens Axboe]

From: Christoph Hellwig <hch@lst.de>

Add a new fsync opcode, which either syncs a range if one is passed,
or the whole file if the offset and length fields are both cleared
to zero.  A flag is provided to use fdatasync semantics, that is only
force out metadata which is required to retrieve the file data, but
not others like metadata.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c                 | 34 ++++++++++++++++++++++++++++++++++
 include/uapi/linux/io_uring.h |  8 +++++++-
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 37ab16007aa6..35d25b49ad94 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4,6 +4,7 @@
  * supporting fast/efficient IO.
  *
  * Copyright (C) 2018-2019 Jens Axboe
+ * Copyright (c) 2018-2019 Christoph Hellwig
  */
 #include <linux/kernel.h>
 #include <linux/init.h>
@@ -466,6 +467,36 @@ static int io_nop(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	return 0;
 }
 
+static int io_fsync(struct io_kiocb *req, const struct io_uring_sqe *sqe,
+		    bool force_nonblock)
+{
+	struct io_ring_ctx *ctx = req->ctx;
+	loff_t end = sqe->off + sqe->len;
+	struct file *file;
+	int ret;
+
+	/* fsync always requires a blocking context */
+	if (force_nonblock)
+		return -EAGAIN;
+
+	if (unlikely(sqe->addr || sqe->ioprio))
+		return -EINVAL;
+	if (unlikely(sqe->fsync_flags & ~IORING_FSYNC_DATASYNC))
+		return -EINVAL;
+
+	file = fget(sqe->fd);
+	if (unlikely(!file))
+		return -EBADF;
+
+	ret = vfs_fsync_range(file, sqe->off, end > 0 ? end : LLONG_MAX,
+			sqe->fsync_flags & IORING_FSYNC_DATASYNC);
+
+	fput(file);
+	io_cqring_add_event(ctx, sqe->user_data, ret, 0);
+	io_free_req(req);
+	return 0;
+}
+
 static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 			   struct sqe_submit *s, bool force_nonblock)
 {
@@ -487,6 +518,9 @@ static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 	case IORING_OP_WRITEV:
 		ret = io_write(req, sqe, force_nonblock);
 		break;
+	case IORING_OP_FSYNC:
+		ret = io_fsync(req, sqe, force_nonblock);
+		break;
 	default:
 		ret = -EINVAL;
 		break;
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index ce65db9269a8..ca503ded73e3 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -26,7 +26,7 @@ struct io_uring_sqe {
 	__u32	len;		/* buffer size or number of iovecs */
 	union {
 		__kernel_rwf_t	rw_flags;
-		__u32		__resv;
+		__u32		fsync_flags;
 	};
 	__u64	user_data;	/* data to be passed back at completion time */
 	__u64	__pad2[3];
@@ -35,6 +35,12 @@ struct io_uring_sqe {
 #define IORING_OP_NOP		0
 #define IORING_OP_READV		1
 #define IORING_OP_WRITEV	2
+#define IORING_OP_FSYNC		3
+
+/*
+ * sqe->fsync_flags
+ */
+#define IORING_FSYNC_DATASYNC	(1 << 0)
 
 /*
  * IO completion data structure (Completion Queue Entry)
-- 
2.17.1

[PATCH 07/13] io_uring: add support for pre-mapped user IO buffers

[Jens Axboe]

If we have fixed user buffers, we can map them into the kernel when we
setup the io_context. That avoids the need to do get_user_pages() for
each and every IO.

To utilize this feature, the application must call io_uring_register()
after having setup an io_uring context, passing in
IORING_REGISTER_BUFFERS as the opcode. The argument must be a pointer
to an iovec array, and the nr_args should contain how many iovecs the
application wishes to map.

If successful, these buffers are now mapped into the kernel, eligible
for IO. To use these fixed buffers, the application must use the
IORING_OP_READ_FIXED and IORING_OP_WRITE_FIXED opcodes, and then
set sqe->index to the desired buffer index. sqe->addr..sqe->addr+seq->len
must point to somewhere inside the indexed buffer.

The application may register buffers throughout the lifetime of the
io_uring context. It can call io_uring_register() with
IORING_UNREGISTER_BUFFERS as the opcode to unregister the current set of
buffers, and then register a new set. The application need not
unregister buffers explicitly before shutting down the io_uring context.

It's perfectly valid to setup a larger buffer, and then sometimes only
use parts of it for an IO. As long as the range is within the originally
mapped region, it will work just fine.

For now, buffers must not be file backed. If file backed buffers are
passed in, the registration will fail with -1/EOPNOTSUPP. This
restriction may be relaxed in the future.

RLIMIT_MEMLOCK is used to check how much memory we can pin. A somewhat
arbitrary 1G per buffer size is also imposed.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 arch/x86/entry/syscalls/syscall_32.tbl |   1 +
 arch/x86/entry/syscalls/syscall_64.tbl |   1 +
 fs/io_uring.c                          | 357 ++++++++++++++++++++++++-
 include/linux/sched/user.h             |   2 +-
 include/linux/syscalls.h               |   2 +
 include/uapi/linux/io_uring.h          |  13 +-
 kernel/sys_ni.c                        |   1 +
 7 files changed, 364 insertions(+), 13 deletions(-)

diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 194e79c0032e..7e89016f8118 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -400,3 +400,4 @@
 386	i386	rseq			sys_rseq			__ia32_sys_rseq
 425	i386	io_uring_setup		sys_io_uring_setup		__ia32_compat_sys_io_uring_setup
 426	i386	io_uring_enter		sys_io_uring_enter		__ia32_sys_io_uring_enter
+427	i386	io_uring_register	sys_io_uring_register		__ia32_sys_io_uring_register
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index 453ff7a79002..8e05d4f05d88 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -345,6 +345,7 @@
 334	common	rseq			__x64_sys_rseq
 425	common	io_uring_setup		__x64_sys_io_uring_setup
 426	common	io_uring_enter		__x64_sys_io_uring_enter
+427	common	io_uring_register	__x64_sys_io_uring_register
 
 #
 # x32-specific system call numbers start at 512 to avoid cache impact
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 497bea0f29c5..63ad09e7cdc7 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -25,8 +25,11 @@
 #include <linux/slab.h>
 #include <linux/workqueue.h>
 #include <linux/blkdev.h>
+#include <linux/bvec.h>
 #include <linux/anon_inodes.h>
 #include <linux/sched/mm.h>
+#include <linux/sizes.h>
+#include <linux/nospec.h>
 
 #include <linux/uaccess.h>
 #include <linux/nospec.h>
@@ -57,6 +60,13 @@ struct io_cq_ring {
 	struct io_uring_cqe	cqes[];
 };
 
+struct io_mapped_ubuf {
+	u64		ubuf;
+	size_t		len;
+	struct		bio_vec *bvec;
+	unsigned int	nr_bvecs;
+};
+
 struct io_ring_ctx {
 	struct {
 		struct percpu_ref	refs;
@@ -90,6 +100,10 @@ struct io_ring_ctx {
 		struct fasync_struct	*cq_fasync;
 	} ____cacheline_aligned_in_smp;
 
+	/* if used, fixed mapped user buffers */
+	unsigned		nr_user_bufs;
+	struct io_mapped_ubuf	*user_bufs;
+
 	struct user_struct	*user;
 
 	struct completion	ctx_done;
@@ -664,12 +678,51 @@ static inline void io_rw_done(struct kiocb *kiocb, ssize_t ret)
 	}
 }
 
+static int io_import_fixed(struct io_ring_ctx *ctx, int rw,
+			   const struct io_uring_sqe *sqe,
+			   struct iov_iter *iter)
+{
+	struct io_mapped_ubuf *imu;
+	size_t len = sqe->len;
+	size_t offset;
+	int index;
+
+	/* attempt to use fixed buffers without having provided iovecs */
+	if (unlikely(!ctx->user_bufs))
+		return -EFAULT;
+	if (unlikely(sqe->buf_index >= ctx->nr_user_bufs))
+		return -EFAULT;
+
+	index = array_index_nospec(sqe->buf_index, ctx->sq_entries);
+	imu = &ctx->user_bufs[index];
+	if ((unsigned long) sqe->addr < imu->ubuf ||
+	    (unsigned long) sqe->addr + len > imu->ubuf + imu->len)
+		return -EFAULT;
+
+	/*
+	 * May not be a start of buffer, set size appropriately
+	 * and advance us to the beginning.
+	 */
+	offset = (unsigned long) sqe->addr - imu->ubuf;
+	iov_iter_bvec(iter, rw, imu->bvec, imu->nr_bvecs, offset + len);
+	if (offset)
+		iov_iter_advance(iter, offset);
+	return 0;
+}
+
 static int io_import_iovec(struct io_ring_ctx *ctx, int rw,
 			   const struct io_uring_sqe *sqe,
 			   struct iovec **iovec, struct iov_iter *iter)
 {
 	void __user *buf = u64_to_user_ptr(sqe->addr);
 
+	if (sqe->opcode == IORING_OP_READ_FIXED ||
+	    sqe->opcode == IORING_OP_WRITE_FIXED) {
+		ssize_t ret = io_import_fixed(ctx, rw, sqe, iter);
+		*iovec = NULL;
+		return ret;
+	}
+
 #ifdef CONFIG_COMPAT
 	if (ctx->compat)
 		return compat_import_iovec(rw, buf, sqe->len, UIO_FASTIOV,
@@ -805,7 +858,7 @@ static int io_fsync(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 
 	if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
 		return -EINVAL;
-	if (unlikely(sqe->addr || sqe->ioprio))
+	if (unlikely(sqe->addr || sqe->ioprio || sqe->buf_index))
 		return -EINVAL;
 	if (unlikely(sqe->fsync_flags & ~IORING_FSYNC_DATASYNC))
 		return -EINVAL;
@@ -840,9 +893,19 @@ static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 		ret = io_nop(req, sqe);
 		break;
 	case IORING_OP_READV:
+		if (unlikely(sqe->buf_index))
+			return -EINVAL;
 		ret = io_read(req, sqe, force_nonblock, state);
 		break;
 	case IORING_OP_WRITEV:
+		if (unlikely(sqe->buf_index))
+			return -EINVAL;
+		ret = io_write(req, sqe, force_nonblock, state);
+		break;
+	case IORING_OP_READ_FIXED:
+		ret = io_read(req, sqe, force_nonblock, state);
+		break;
+	case IORING_OP_WRITE_FIXED:
 		ret = io_write(req, sqe, force_nonblock, state);
 		break;
 	case IORING_OP_FSYNC:
@@ -865,14 +928,21 @@ static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 	return 0;
 }
 
+static inline bool io_sqe_needs_user(const struct io_uring_sqe *sqe)
+{
+	return !(sqe->opcode == IORING_OP_READ_FIXED ||
+		 sqe->opcode == IORING_OP_WRITE_FIXED);
+}
+
 static void io_sq_wq_submit_work(struct work_struct *work)
 {
 	struct io_kiocb *req = container_of(work, struct io_kiocb, work);
 	struct sqe_submit *s = &req->submit;
 	u64 user_data = s->sqe->user_data;
 	struct io_ring_ctx *ctx = req->ctx;
-	mm_segment_t old_fs = get_fs();
 	struct files_struct *old_files;
+	mm_segment_t old_fs;
+	bool needs_user;
 	int ret;
 
 	 /* Ensure we clear previously set forced non-block flag */
@@ -881,19 +951,28 @@ static void io_sq_wq_submit_work(struct work_struct *work)
 	old_files = current->files;
 	current->files = ctx->sqo_files;
 
-	if (!mmget_not_zero(ctx->sqo_mm)) {
-		ret = -EFAULT;
-		goto err;
+	/*
+	 * If we're doing IO to fixed buffers, we don't need to get/set
+	 * user context
+	 */
+	needs_user = io_sqe_needs_user(s->sqe);
+	if (needs_user) {
+		if (!mmget_not_zero(ctx->sqo_mm)) {
+			ret = -EFAULT;
+			goto err;
+		}
+		use_mm(ctx->sqo_mm);
+		old_fs = get_fs();
+		set_fs(USER_DS);
 	}
 
-	use_mm(ctx->sqo_mm);
-	set_fs(USER_DS);
-
 	ret = __io_submit_sqe(ctx, req, s, false, NULL);
 
-	set_fs(old_fs);
-	unuse_mm(ctx->sqo_mm);
-	mmput(ctx->sqo_mm);
+	if (needs_user) {
+		set_fs(old_fs);
+		unuse_mm(ctx->sqo_mm);
+		mmput(ctx->sqo_mm);
+	}
 err:
 	if (ret) {
 		io_cqring_add_event(ctx, user_data, ret, 0);
@@ -1163,6 +1242,14 @@ static int __io_account_mem(struct user_struct *user, unsigned long nr_pages)
 	return 0;
 }
 
+static int io_account_mem(struct io_ring_ctx *ctx, unsigned long nr_pages)
+{
+	if (ctx->user)
+		return __io_account_mem(ctx->user, nr_pages);
+
+	return 0;
+}
+
 static unsigned long ring_pages(unsigned sq_entries, unsigned cq_entries)
 {
 	struct io_sq_ring *sq_ring;
@@ -1176,6 +1263,190 @@ static unsigned long ring_pages(unsigned sq_entries, unsigned cq_entries)
 	return (bytes + PAGE_SIZE - 1) / PAGE_SIZE;
 }
 
+static int io_sqe_buffer_unregister(struct io_ring_ctx *ctx)
+{
+	int i, j;
+
+	if (!ctx->user_bufs)
+		return -ENXIO;
+
+	for (i = 0; i < ctx->sq_entries; i++) {
+		struct io_mapped_ubuf *imu = &ctx->user_bufs[i];
+
+		for (j = 0; j < imu->nr_bvecs; j++)
+			put_page(imu->bvec[j].bv_page);
+
+		io_unaccount_mem(ctx, imu->nr_bvecs);
+		kfree(imu->bvec);
+		imu->nr_bvecs = 0;
+	}
+
+	kfree(ctx->user_bufs);
+	ctx->user_bufs = NULL;
+	free_uid(ctx->user);
+	ctx->user = NULL;
+	return 0;
+}
+
+static int io_copy_iov(struct io_ring_ctx *ctx, struct iovec *dst,
+		       void __user *arg, unsigned index)
+{
+	struct iovec __user *src;
+
+#ifdef CONFIG_COMPAT
+	if (ctx->compat) {
+		struct compat_iovec __user *ciovs;
+		struct compat_iovec ciov;
+
+		ciovs = (struct compat_iovec __user *) arg;
+		if (copy_from_user(&ciov, &ciovs[index], sizeof(ciov)))
+			return -EFAULT;
+
+		dst->iov_base = (void __user *) (unsigned long) ciov.iov_base;
+		dst->iov_len = ciov.iov_len;
+		return 0;
+	}
+#endif
+	src = (struct iovec __user *) arg;
+	if (copy_from_user(dst, &src[index], sizeof(*dst)))
+		return -EFAULT;
+	return 0;
+}
+
+static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg,
+				  unsigned nr_args)
+{
+	struct vm_area_struct **vmas = NULL;
+	struct page **pages = NULL;
+	int i, j, got_pages = 0;
+	int ret = -EINVAL;
+
+	if (ctx->user_bufs)
+		return -EBUSY;
+	if (!nr_args || nr_args > UIO_MAXIOV)
+		return -EINVAL;
+
+	ctx->user_bufs = kcalloc(nr_args, sizeof(struct io_mapped_ubuf),
+					GFP_KERNEL);
+	if (!ctx->user_bufs)
+		return -ENOMEM;
+
+	if (!capable(CAP_IPC_LOCK))
+		ctx->user = get_uid(current_user());
+
+	for (i = 0; i < nr_args; i++) {
+		struct io_mapped_ubuf *imu = &ctx->user_bufs[i];
+		unsigned long off, start, end, ubuf;
+		int pret, nr_pages;
+		struct iovec iov;
+		size_t size;
+
+		ret = io_copy_iov(ctx, &iov, arg, i);
+		if (ret)
+			break;
+
+		/*
+		 * Don't impose further limits on the size and buffer
+		 * constraints here, we'll -EINVAL later when IO is
+		 * submitted if they are wrong.
+		 */
+		ret = -EFAULT;
+		if (!iov.iov_base)
+			goto err;
+
+		/* arbitrary limit, but we need something */
+		if (iov.iov_len > SZ_1G)
+			goto err;
+
+		ubuf = (unsigned long) iov.iov_base;
+		end = (ubuf + iov.iov_len + PAGE_SIZE - 1) >> PAGE_SHIFT;
+		start = ubuf >> PAGE_SHIFT;
+		nr_pages = end - start;
+
+		ret = io_account_mem(ctx, nr_pages);
+		if (ret)
+			goto err;
+
+		if (!pages || nr_pages > got_pages) {
+			kfree(vmas);
+			kfree(pages);
+			pages = kmalloc_array(nr_pages, sizeof(struct page *),
+						GFP_KERNEL);
+			vmas = kmalloc_array(nr_pages,
+					sizeof(struct vma_area_struct *),
+					GFP_KERNEL);
+			if (!pages || !vmas) {
+				io_unaccount_mem(ctx, nr_pages);
+				goto err;
+			}
+			got_pages = nr_pages;
+		}
+
+		imu->bvec = kmalloc_array(nr_pages, sizeof(struct bio_vec),
+						GFP_KERNEL);
+		if (!imu->bvec) {
+			io_unaccount_mem(ctx, nr_pages);
+			goto err;
+		}
+
+		down_write(&current->mm->mmap_sem);
+		pret = get_user_pages_longterm(ubuf, nr_pages, FOLL_WRITE,
+						pages, vmas);
+		if (pret == nr_pages) {
+			/* don't support file backed memory */
+			for (j = 0; j < nr_pages; j++) {
+				struct vm_area_struct *vma = vmas[j];
+
+				if (vma->vm_file) {
+					ret = -EOPNOTSUPP;
+					break;
+				}
+			}
+		} else {
+			ret = pret < 0 ? pret : -EFAULT;
+		}
+		up_write(&current->mm->mmap_sem);
+		if (ret) {
+			/*
+			 * if we did partial map, or found file backed vmas,
+			 * release any pages we did get
+			 */
+			if (pret > 0) {
+				for (j = 0; j < pret; j++)
+					put_page(pages[j]);
+			}
+			io_unaccount_mem(ctx, nr_pages);
+			goto err;
+		}
+
+		off = ubuf & ~PAGE_MASK;
+		size = iov.iov_len;
+		for (j = 0; j < nr_pages; j++) {
+			size_t vec_len;
+
+			vec_len = min_t(size_t, size, PAGE_SIZE - off);
+			imu->bvec[j].bv_page = pages[j];
+			imu->bvec[j].bv_len = vec_len;
+			imu->bvec[j].bv_offset = off;
+			off = 0;
+			size -= vec_len;
+		}
+		/* store original address for later verification */
+		imu->ubuf = ubuf;
+		imu->len = iov.iov_len;
+		imu->nr_bvecs = nr_pages;
+	}
+	kfree(pages);
+	kfree(vmas);
+	ctx->nr_user_bufs = nr_args;
+	return 0;
+err:
+	kfree(pages);
+	kfree(vmas);
+	io_sqe_buffer_unregister(ctx);
+	return ret;
+}
+
 static void io_free_scq_urings(struct io_ring_ctx *ctx)
 {
 	if (ctx->sq_ring) {
@@ -1197,6 +1468,7 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx)
 	io_sq_offload_stop(ctx);
 	io_iopoll_reap_events(ctx);
 	io_free_scq_urings(ctx);
+	io_sqe_buffer_unregister(ctx);
 	percpu_ref_exit(&ctx->refs);
 	io_unaccount_mem(ctx, ring_pages(ctx->sq_entries, ctx->cq_entries));
 	kfree(ctx);
@@ -1488,6 +1760,69 @@ COMPAT_SYSCALL_DEFINE2(io_uring_setup, u32, entries,
 }
 #endif
 
+static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
+			       void __user *arg, unsigned nr_args)
+{
+	int ret;
+
+	/* Drop our initial ref and wait for the ctx to be fully idle */
+	percpu_ref_put(&ctx->refs);
+	percpu_ref_kill(&ctx->refs);
+	wait_for_completion(&ctx->ctx_done);
+
+	switch (opcode) {
+	case IORING_REGISTER_BUFFERS:
+		ret = io_sqe_buffer_register(ctx, arg, nr_args);
+		break;
+	case IORING_UNREGISTER_BUFFERS:
+		ret = -EINVAL;
+		if (arg || nr_args)
+			break;
+		ret = io_sqe_buffer_unregister(ctx);
+		break;
+	default:
+		ret = -EINVAL;
+		break;
+	}
+
+	/* bring the ctx back to life */
+	reinit_completion(&ctx->ctx_done);
+	percpu_ref_resurrect(&ctx->refs);
+	percpu_ref_get(&ctx->refs);
+	return ret;
+}
+
+SYSCALL_DEFINE4(io_uring_register, unsigned int, fd, unsigned int, opcode,
+		void __user *, arg, unsigned int, nr_args)
+{
+	struct io_ring_ctx *ctx;
+	long ret = -EBADF;
+	struct fd f;
+
+	f = fdget(fd);
+	if (!f.file)
+		return -EBADF;
+
+	ret = -EOPNOTSUPP;
+	if (f.file->f_op != &io_uring_fops)
+		goto out_fput;
+
+	ret = -ENXIO;
+	ctx = f.file->private_data;
+	if (!percpu_ref_tryget(&ctx->refs))
+		goto out_fput;
+
+	ret = -EBUSY;
+	if (mutex_trylock(&ctx->uring_lock)) {
+		ret = __io_uring_register(ctx, opcode, arg, nr_args);
+		mutex_unlock(&ctx->uring_lock);
+	}
+	io_ring_drop_ctx_refs(ctx, 1);
+out_fput:
+	fdput(f);
+	return ret;
+}
+
 static int __init io_uring_init(void)
 {
 	req_cachep = KMEM_CACHE(io_kiocb, SLAB_HWCACHE_ALIGN | SLAB_PANIC);
diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h
index 39ad98c09c58..c7b5f86b91a1 100644
--- a/include/linux/sched/user.h
+++ b/include/linux/sched/user.h
@@ -40,7 +40,7 @@ struct user_struct {
 	kuid_t uid;
 
 #if defined(CONFIG_PERF_EVENTS) || defined(CONFIG_BPF_SYSCALL) || \
-    defined(CONFIG_NET)
+    defined(CONFIG_NET) || defined(CONFIG_IO_URING)
 	atomic_long_t locked_vm;
 #endif
 
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 542757a4c898..101f7024d154 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -314,6 +314,8 @@ asmlinkage long sys_io_uring_setup(u32 entries,
 				struct io_uring_params __user *p);
 asmlinkage long sys_io_uring_enter(unsigned int fd, u32 to_submit,
 				u32 min_complete, u32 flags);
+asmlinkage long sys_io_uring_register(unsigned int fd, unsigned int op,
+				void __user *arg, unsigned int nr_args);
 
 /* fs/xattr.c */
 asmlinkage long sys_setxattr(const char __user *path, const char __user *name,
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 4fc5fbd07688..03ce7133c3b2 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -29,7 +29,10 @@ struct io_uring_sqe {
 		__u32		fsync_flags;
 	};
 	__u64	user_data;	/* data to be passed back at completion time */
-	__u64	__pad2[3];
+	union {
+		__u16	buf_index;	/* index into fixed buffers, if used */
+		__u64	__pad2[3];
+	};
 };
 
 /*
@@ -41,6 +44,8 @@ struct io_uring_sqe {
 #define IORING_OP_READV		1
 #define IORING_OP_WRITEV	2
 #define IORING_OP_FSYNC		3
+#define IORING_OP_READ_FIXED	4
+#define IORING_OP_WRITE_FIXED	5
 
 /*
  * sqe->fsync_flags
@@ -104,4 +109,10 @@ struct io_uring_params {
 	struct io_cqring_offsets cq_off;
 };
 
+/*
+ * io_uring_register(2) opcodes and arguments
+ */
+#define IORING_REGISTER_BUFFERS		0
+#define IORING_UNREGISTER_BUFFERS	1
+
 #endif
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index d754811ec780..38567718c397 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -49,6 +49,7 @@ COND_SYSCALL_COMPAT(io_pgetevents);
 COND_SYSCALL(io_uring_setup);
 COND_SYSCALL_COMPAT(io_uring_setup);
 COND_SYSCALL(io_uring_enter);
+COND_SYSCALL(io_uring_register);
 
 /* fs/xattr.c */
 
-- 
2.17.1

[PATCH 07/18] io_uring: support for IO polling

[Jens Axboe]

Add support for a polled io_uring context. When a read or write is
submitted to a polled context, the application must poll for completions
on the CQ ring through io_uring_enter(2). Polled IO may not generate
IRQ completions, hence they need to be actively found by the application
itself.

To use polling, io_uring_setup() must be used with the
IORING_SETUP_IOPOLL flag being set. It is illegal to mix and match
polled and non-polled IO on an io_uring.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c                 | 263 ++++++++++++++++++++++++++++++++--
 include/uapi/linux/io_uring.h |   5 +
 2 files changed, 257 insertions(+), 11 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 35d25b49ad94..f17c2dc73e40 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -101,6 +101,8 @@ struct io_ring_ctx {
 
 	struct {
 		spinlock_t		completion_lock;
+		unsigned		poll_multi_file;
+		struct list_head	poll_list;
 	} ____cacheline_aligned_in_smp;
 };
 
@@ -119,12 +121,16 @@ struct io_kiocb {
 	struct list_head	list;
 	unsigned int		flags;
 #define REQ_F_FORCE_NONBLOCK	1	/* inline submission attempt */
+#define REQ_F_IOPOLL_COMPLETED	2	/* polled IO has completed */
+#define REQ_F_IOPOLL_EAGAIN	4	/* submission got EAGAIN */
 	u64			user_data;
+	u64			res;
 
 	struct work_struct	work;
 };
 
 #define IO_PLUG_THRESHOLD		2
+#define IO_IOPOLL_BATCH			8
 
 static struct kmem_cache *req_cachep;
 
@@ -156,6 +162,7 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 	mutex_init(&ctx->uring_lock);
 	init_waitqueue_head(&ctx->wait);
 	spin_lock_init(&ctx->completion_lock);
+	INIT_LIST_HEAD(&ctx->poll_list);
 	return ctx;
 }
 
@@ -191,8 +198,8 @@ static struct io_uring_cqe *io_get_cqring(struct io_ring_ctx *ctx)
 	return &ring->cqes[tail & ctx->cq_mask];
 }
 
-static void __io_cqring_add_event(struct io_ring_ctx *ctx, u64 ki_user_data,
-				  long res, unsigned ev_flags)
+static void io_cqring_fill_event(struct io_ring_ctx *ctx, u64 ki_user_data,
+				 long res, unsigned ev_flags)
 {
 	struct io_uring_cqe *cqe;
 
@@ -206,9 +213,15 @@ static void __io_cqring_add_event(struct io_ring_ctx *ctx, u64 ki_user_data,
 		cqe->user_data = ki_user_data;
 		cqe->res = res;
 		cqe->flags = ev_flags;
-		io_commit_cqring(ctx);
 	} else
 		ctx->cq_ring->overflow++;
+}
+
+static void __io_cqring_add_event(struct io_ring_ctx *ctx, u64 ki_user_data,
+				  long res, unsigned ev_flags)
+{
+	io_cqring_fill_event(ctx, ki_user_data, res, ev_flags);
+	io_commit_cqring(ctx);
 
 	if (waitqueue_active(&ctx->wait))
 		wake_up(&ctx->wait);
@@ -250,12 +263,158 @@ static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx)
 	return NULL;
 }
 
+static void io_free_req_many(struct io_ring_ctx *ctx, void **reqs, int *nr)
+{
+	if (*nr) {
+		kmem_cache_free_bulk(req_cachep, *nr, reqs);
+		io_ring_drop_ctx_refs(ctx, *nr);
+		*nr = 0;
+	}
+}
+
 static void io_free_req(struct io_kiocb *req)
 {
 	io_ring_drop_ctx_refs(req->ctx, 1);
 	kmem_cache_free(req_cachep, req);
 }
 
+/*
+ * Find and free completed poll iocbs
+ */
+static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
+			       struct list_head *done)
+{
+	void *reqs[IO_IOPOLL_BATCH];
+	struct io_kiocb *req;
+	int to_free = 0;
+
+	while (!list_empty(done)) {
+		req = list_first_entry(done, struct io_kiocb, list);
+		list_del(&req->list);
+
+		io_cqring_fill_event(ctx, req->user_data, req->res, 0);
+
+		reqs[to_free++] = req;
+		(*nr_events)++;
+
+		fput(req->rw.ki_filp);
+		if (to_free == ARRAY_SIZE(reqs))
+			io_free_req_many(ctx, reqs, &to_free);
+	}
+	io_commit_cqring(ctx);
+
+	if (to_free)
+		io_free_req_many(ctx, reqs, &to_free);
+}
+
+static int io_do_iopoll(struct io_ring_ctx *ctx, unsigned int *nr_events,
+			long min)
+{
+	struct io_kiocb *req, *tmp;
+	LIST_HEAD(done);
+	bool spin;
+	int ret;
+
+	/*
+	 * Only spin for completions if we don't have multiple devices hanging
+	 * off our complete list, and we're under the requested amount.
+	 */
+	spin = !ctx->poll_multi_file && (*nr_events < min);
+
+	ret = 0;
+	list_for_each_entry_safe(req, tmp, &ctx->poll_list, list) {
+		struct kiocb *kiocb = &req->rw;
+
+		/*
+		 * Move completed entries to our local list. If we find a
+		 * request that requires polling, break out and complete
+		 * the done list first, if we have entries there.
+		 */
+		if (req->flags & REQ_F_IOPOLL_COMPLETED) {
+			list_move_tail(&req->list, &done);
+			continue;
+		}
+		if (!list_empty(&done))
+			break;
+
+		ret = kiocb->ki_filp->f_op->iopoll(kiocb, spin);
+		if (ret < 0)
+			break;
+
+		if (ret && spin)
+			spin = false;
+		ret = 0;
+	}
+
+	if (!list_empty(&done))
+		io_iopoll_complete(ctx, nr_events, &done);
+
+	return ret;
+}
+
+/*
+ * Poll for a mininum of 'min' events. Note that if min == 0 we consider that a
+ * non-spinning poll check - we'll still enter the driver poll loop, but only
+ * as a non-spinning completion check.
+ */
+static int io_iopoll_getevents(struct io_ring_ctx *ctx, unsigned int *nr_events,
+				long min)
+{
+	int ret;
+
+	do {
+		if (list_empty(&ctx->poll_list))
+			return 0;
+
+		ret = io_do_iopoll(ctx, nr_events, min);
+		if (ret < 0)
+			break;
+	} while (min && *nr_events < min);
+
+	if (ret < 0)
+		return ret;
+
+	return *nr_events < min;
+}
+
+/*
+ * We can't just wait for polled events to come to us, we have to actively
+ * find and complete them.
+ */
+static void io_iopoll_reap_events(struct io_ring_ctx *ctx)
+{
+	if (!(ctx->flags & IORING_SETUP_IOPOLL))
+		return;
+
+	mutex_lock(&ctx->uring_lock);
+	while (!list_empty(&ctx->poll_list)) {
+		unsigned int nr_events = 0;
+
+		io_iopoll_getevents(ctx, &nr_events, 1);
+	}
+	mutex_unlock(&ctx->uring_lock);
+}
+
+static int io_iopoll_check(struct io_ring_ctx *ctx, unsigned *nr_events,
+			   long min)
+{
+	int ret = 0;
+
+	while (!*nr_events || !need_resched()) {
+		int tmin = 0;
+
+		if (*nr_events < min)
+			tmin = min - *nr_events;
+
+		ret = io_iopoll_getevents(ctx, nr_events, tmin);
+		if (ret <= 0)
+			break;
+		ret = 0;
+	}
+
+	return ret;
+}
+
 static void kiocb_end_write(struct kiocb *kiocb)
 {
 	if (kiocb->ki_flags & IOCB_WRITE) {
@@ -282,9 +441,60 @@ static void io_complete_rw(struct kiocb *kiocb, long res, long res2)
 	io_free_req(req);
 }
 
+static void io_complete_rw_iopoll(struct kiocb *kiocb, long res, long res2)
+{
+	struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw);
+
+	kiocb_end_write(kiocb);
+
+	if (unlikely(res == -EAGAIN)) {
+		req->flags |= REQ_F_IOPOLL_EAGAIN;
+	} else {
+		req->flags |= REQ_F_IOPOLL_COMPLETED;
+		req->res = res;
+	}
+}
+
+/*
+ * After the iocb has been issued, it's safe to be found on the poll list.
+ * Adding the kiocb to the list AFTER submission ensures that we don't
+ * find it from a io_iopoll_getevents() thread before the issuer is done
+ * accessing the kiocb cookie.
+ */
+static void io_iopoll_req_issued(struct io_kiocb *req)
+{
+	struct io_ring_ctx *ctx = req->ctx;
+
+	/*
+	 * Track whether we have multiple files in our lists. This will impact
+	 * how we do polling eventually, not spinning if we're on potentially
+	 * different devices.
+	 */
+	if (list_empty(&ctx->poll_list)) {
+		ctx->poll_multi_file = 0;
+	} else if (!ctx->poll_multi_file) {
+		struct io_kiocb *list_req;
+
+		list_req = list_first_entry(&ctx->poll_list, struct io_kiocb,
+						list);
+		if (list_req->rw.ki_filp != req->rw.ki_filp)
+			ctx->poll_multi_file = 1;
+	}
+
+	/*
+	 * For fast devices, IO may have already completed. If it has, add
+	 * it to the front so we find it first.
+	 */
+	if (req->flags & REQ_F_IOPOLL_COMPLETED)
+		list_add(&req->list, &ctx->poll_list);
+	else
+		list_add_tail(&req->list, &ctx->poll_list);
+}
+
 static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 		      bool force_nonblock)
 {
+	struct io_ring_ctx *ctx = req->ctx;
 	struct kiocb *kiocb = &req->rw;
 	int ret;
 
@@ -310,12 +520,21 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 		kiocb->ki_flags |= IOCB_NOWAIT;
 		req->flags |= REQ_F_FORCE_NONBLOCK;
 	}
-	if (kiocb->ki_flags & IOCB_HIPRI) {
-		ret = -EINVAL;
-		goto out_fput;
-	}
+	if (ctx->flags & IORING_SETUP_IOPOLL) {
+		ret = -EOPNOTSUPP;
+		if (!(kiocb->ki_flags & IOCB_DIRECT) ||
+		    !kiocb->ki_filp->f_op->iopoll)
+			goto out_fput;
 
-	kiocb->ki_complete = io_complete_rw;
+		kiocb->ki_flags |= IOCB_HIPRI;
+		kiocb->ki_complete = io_complete_rw_iopoll;
+	} else {
+		if (kiocb->ki_flags & IOCB_HIPRI) {
+			ret = -EINVAL;
+			goto out_fput;
+		}
+		kiocb->ki_complete = io_complete_rw;
+	}
 	return 0;
 out_fput:
 	fput(kiocb->ki_filp);
@@ -462,6 +681,9 @@ static int io_nop(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 {
 	struct io_ring_ctx *ctx = req->ctx;
 
+	if (unlikely(ctx->flags & IORING_SETUP_IOPOLL))
+		return -EINVAL;
+
 	__io_cqring_add_event(ctx, sqe->user_data, 0, 0);
 	io_free_req(req);
 	return 0;
@@ -479,6 +701,8 @@ static int io_fsync(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	if (force_nonblock)
 		return -EAGAIN;
 
+	if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
+		return -EINVAL;
 	if (unlikely(sqe->addr || sqe->ioprio))
 		return -EINVAL;
 	if (unlikely(sqe->fsync_flags & ~IORING_FSYNC_DATASYNC))
@@ -526,7 +750,16 @@ static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 		break;
 	}
 
-	return ret;
+	if (ret)
+		return ret;
+
+	if (ctx->flags & IORING_SETUP_IOPOLL) {
+		if (req->flags & REQ_F_IOPOLL_EAGAIN)
+			return -EAGAIN;
+		io_iopoll_req_issued(req);
+	}
+
+	return 0;
 }
 
 static void io_sq_wq_submit_work(struct work_struct *work)
@@ -712,12 +945,18 @@ static int __io_uring_enter(struct io_ring_ctx *ctx, unsigned to_submit,
 			return ret;
 	}
 	if (flags & IORING_ENTER_GETEVENTS) {
+		unsigned nr_events = 0;
 		int get_ret;
 
 		if (!ret && to_submit)
 			min_complete = 0;
 
-		get_ret = io_cqring_wait(ctx, min_complete);
+		if (ctx->flags & IORING_SETUP_IOPOLL)
+			get_ret = io_iopoll_check(ctx, &nr_events,
+							min_complete);
+		else
+			get_ret = io_cqring_wait(ctx, min_complete);
+
 		if (get_ret < 0 && !ret)
 			ret = get_ret;
 	}
@@ -826,6 +1065,7 @@ static void io_free_scq_urings(struct io_ring_ctx *ctx)
 static void io_ring_ctx_free(struct io_ring_ctx *ctx)
 {
 	io_sq_offload_stop(ctx);
+	io_iopoll_reap_events(ctx);
 	io_free_scq_urings(ctx);
 	percpu_ref_exit(&ctx->refs);
 	io_unaccount_mem(ctx, ring_pages(ctx->sq_entries, ctx->cq_entries));
@@ -860,6 +1100,7 @@ static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
 	percpu_ref_kill(&ctx->refs);
 	mutex_unlock(&ctx->uring_lock);
 
+	io_iopoll_reap_events(ctx);
 	wait_for_completion(&ctx->ctx_done);
 	io_ring_ctx_free(ctx);
 }
@@ -1090,7 +1331,7 @@ static long io_uring_setup(u32 entries, struct io_uring_params __user *params,
 			return -EINVAL;
 	}
 
-	if (p.flags)
+	if (p.flags & ~IORING_SETUP_IOPOLL)
 		return -EINVAL;
 
 	ret = io_uring_create(entries, &p, compat);
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index ca503ded73e3..4fc5fbd07688 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -32,6 +32,11 @@ struct io_uring_sqe {
 	__u64	__pad2[3];
 };
 
+/*
+ * io_uring_setup() flags
+ */
+#define IORING_SETUP_IOPOLL	(1 << 0)	/* io_context is polled */
+
 #define IORING_OP_NOP		0
 #define IORING_OP_READV		1
 #define IORING_OP_WRITEV	2
-- 
2.17.1

Re: [PATCH 07/18] io_uring: support for IO polling

[Christoph Hellwig]

>  	struct {
>  		spinlock_t		completion_lock;
> +		unsigned		poll_multi_file;

This seems to be used as a bool.

>  
> -static void __io_cqring_add_event(struct io_ring_ctx *ctx, u64 ki_user_data,
> -				  long res, unsigned ev_flags)
> +static void io_cqring_fill_event(struct io_ring_ctx *ctx, u64 ki_user_data,
> +				 long res, unsigned ev_flags)
>  {
>  	struct io_uring_cqe *cqe;
>  
> @@ -206,9 +213,15 @@ static void __io_cqring_add_event(struct io_ring_ctx *ctx, u64 ki_user_data,
>  		cqe->user_data = ki_user_data;
>  		cqe->res = res;
>  		cqe->flags = ev_flags;
> -		io_commit_cqring(ctx);
>  	} else
>  		ctx->cq_ring->overflow++;
> +}

Maybe we should have created this low-level helper already in the
patch introducing the code?

Re: [PATCH 07/18] io_uring: support for IO polling

[Jens Axboe]

On 1/28/19 8:02 AM, Christoph Hellwig wrote:
>>  	struct {
>>  		spinlock_t		completion_lock;
>> +		unsigned		poll_multi_file;
> 
> This seems to be used as a bool.

Fixed

>> -static void __io_cqring_add_event(struct io_ring_ctx *ctx, u64 ki_user_data,
>> -				  long res, unsigned ev_flags)
>> +static void io_cqring_fill_event(struct io_ring_ctx *ctx, u64 ki_user_data,
>> +				 long res, unsigned ev_flags)
>>  {
>>  	struct io_uring_cqe *cqe;
>>  
>> @@ -206,9 +213,15 @@ static void __io_cqring_add_event(struct io_ring_ctx *ctx, u64 ki_user_data,
>>  		cqe->user_data = ki_user_data;
>>  		cqe->res = res;
>>  		cqe->flags = ev_flags;
>> -		io_commit_cqring(ctx);
>>  	} else
>>  		ctx->cq_ring->overflow++;
>> +}
> 
> Maybe we should have created this low-level helper already in the
> patch introducing the code?

I think that can go both ways. If we create it early, it'll just be a
pointless helper. Don't really care too much about this particular case.

-- 
Jens Axboe

Re: [PATCH 07/18] io_uring: support for IO polling

[Christoph Hellwig]

On Mon, Jan 28, 2019 at 09:46:17AM -0700, Jens Axboe wrote:
> I think that can go both ways. If we create it early, it'll just be a
> pointless helper. Don't really care too much about this particular case.

Without the no-op locking fix we don't really need the current
__io_cqring_add_event anymore, so we'd still have two somewhat
reasonably defined helpers.

Re: [PATCH 07/18] io_uring: support for IO polling

[Jens Axboe]

On 1/28/19 11:27 PM, Christoph Hellwig wrote:
> On Mon, Jan 28, 2019 at 09:46:17AM -0700, Jens Axboe wrote:
>> I think that can go both ways. If we create it early, it'll just be a
>> pointless helper. Don't really care too much about this particular case.
> 
> Without the no-op locking fix we don't really need the current
> __io_cqring_add_event anymore, so we'd still have two somewhat
> reasonably defined helpers.

Yeah, killed it, which also fixes your complaint about adding a new
helper in the poll patch.

-- 
Jens Axboe

[PATCH 08/18] fs: add fget_many() and fput_many()

[Jens Axboe]

Some uses cases repeatedly get and put references to the same file, but
the only exposed interface is doing these one at the time. As each of
these entail an atomic inc or dec on a shared structure, that cost can
add up.

Add fget_many(), which works just like fget(), except it takes an
argument for how many references to get on the file. Ditto fput_many(),
which can drop an arbitrary number of references to a file.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/file.c            | 15 ++++++++++-----
 fs/file_table.c      |  9 +++++++--
 include/linux/file.h |  2 ++
 include/linux/fs.h   |  4 +++-
 4 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/fs/file.c b/fs/file.c
index 3209ee271c41..e0d7ce70e860 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -705,7 +705,7 @@ void do_close_on_exec(struct files_struct *files)
 	spin_unlock(&files->file_lock);
 }
 
-static struct file *__fget(unsigned int fd, fmode_t mask)
+static struct file *__fget(unsigned int fd, fmode_t mask, unsigned int refs)
 {
 	struct files_struct *files = current->files;
 	struct file *file;
@@ -720,7 +720,7 @@ static struct file *__fget(unsigned int fd, fmode_t mask)
 		 */
 		if (file->f_mode & mask)
 			file = NULL;
-		else if (!get_file_rcu(file))
+		else if (!get_file_rcu_many(file, refs))
 			goto loop;
 	}
 	rcu_read_unlock();
@@ -728,15 +728,20 @@ static struct file *__fget(unsigned int fd, fmode_t mask)
 	return file;
 }
 
+struct file *fget_many(unsigned int fd, unsigned int refs)
+{
+	return __fget(fd, FMODE_PATH, refs);
+}
+
 struct file *fget(unsigned int fd)
 {
-	return __fget(fd, FMODE_PATH);
+	return fget_many(fd, 1);
 }
 EXPORT_SYMBOL(fget);
 
 struct file *fget_raw(unsigned int fd)
 {
-	return __fget(fd, 0);
+	return __fget(fd, 0, 1);
 }
 EXPORT_SYMBOL(fget_raw);
 
@@ -767,7 +772,7 @@ static unsigned long __fget_light(unsigned int fd, fmode_t mask)
 			return 0;
 		return (unsigned long)file;
 	} else {
-		file = __fget(fd, mask);
+		file = __fget(fd, mask, 1);
 		if (!file)
 			return 0;
 		return FDPUT_FPUT | (unsigned long)file;
diff --git a/fs/file_table.c b/fs/file_table.c
index 5679e7fcb6b0..155d7514a094 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -326,9 +326,9 @@ void flush_delayed_fput(void)
 
 static DECLARE_DELAYED_WORK(delayed_fput_work, delayed_fput);
 
-void fput(struct file *file)
+void fput_many(struct file *file, unsigned int refs)
 {
-	if (atomic_long_dec_and_test(&file->f_count)) {
+	if (atomic_long_sub_and_test(refs, &file->f_count)) {
 		struct task_struct *task = current;
 
 		if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) {
@@ -347,6 +347,11 @@ void fput(struct file *file)
 	}
 }
 
+void fput(struct file *file)
+{
+	fput_many(file, 1);
+}
+
 /*
  * synchronous analog of fput(); for kernel threads that might be needed
  * in some umount() (and thus can't use flush_delayed_fput() without
diff --git a/include/linux/file.h b/include/linux/file.h
index 6b2fb032416c..3fcddff56bc4 100644
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -13,6 +13,7 @@
 struct file;
 
 extern void fput(struct file *);
+extern void fput_many(struct file *, unsigned int);
 
 struct file_operations;
 struct vfsmount;
@@ -44,6 +45,7 @@ static inline void fdput(struct fd fd)
 }
 
 extern struct file *fget(unsigned int fd);
+extern struct file *fget_many(unsigned int fd, unsigned int refs);
 extern struct file *fget_raw(unsigned int fd);
 extern unsigned long __fdget(unsigned int fd);
 extern unsigned long __fdget_raw(unsigned int fd);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index ccb0b7a63aa5..acaad78b6781 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -952,7 +952,9 @@ static inline struct file *get_file(struct file *f)
 	atomic_long_inc(&f->f_count);
 	return f;
 }
-#define get_file_rcu(x) atomic_long_inc_not_zero(&(x)->f_count)
+#define get_file_rcu_many(x, cnt)	\
+	atomic_long_add_unless(&(x)->f_count, (cnt), 0)
+#define get_file_rcu(x) get_file_rcu_many((x), 1)
 #define fput_atomic(x)	atomic_long_add_unless(&(x)->f_count, -1, 1)
 #define file_count(x)	atomic_long_read(&(x)->f_count)
 
-- 
2.17.1

Re: [PATCH 08/18] fs: add fget_many() and fput_many()

[Christoph Hellwig]

> +struct file *fget_many(unsigned int fd, unsigned int refs)
> +{
> +	return __fget(fd, FMODE_PATH, refs);
> +}
> +
>  struct file *fget(unsigned int fd)
>  {
> -	return __fget(fd, FMODE_PATH);
> +	return fget_many(fd, 1);

I'd still prefer removing the double indirection in this call, but
I know you disagree.

>  }
>  EXPORT_SYMBOL(fget);
>  
>  struct file *fget_raw(unsigned int fd)
>  {
> -	return __fget(fd, 0);
> +	return __fget(fd, 0, 1);
>  }
>  EXPORT_SYMBOL(fget_raw);

Especially as we already avoid it here..

Otherwise looks fine to me:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH 08/18] fs: add fget_many() and fput_many()

[Jens Axboe]

On 1/28/19 7:29 AM, Christoph Hellwig wrote:
>> +struct file *fget_many(unsigned int fd, unsigned int refs)
>> +{
>> +	return __fget(fd, FMODE_PATH, refs);
>> +}
>> +
>>  struct file *fget(unsigned int fd)
>>  {
>> -	return __fget(fd, FMODE_PATH);
>> +	return fget_many(fd, 1);
> 
> I'd still prefer removing the double indirection in this call, but
> I know you disagree.

Not a big deal, I can kill it.

-- 
Jens Axboe

[PATCH 08/13] io_uring: add file set registration

[Jens Axboe]

We normally have to fget/fput for each IO we do on a file. Even with
the batching we do, the cost of the atomic inc/dec of the file usage
count adds up.

This adds IORING_REGISTER_FILES, and IORING_UNREGISTER_FILES opcodes
for the io_uring_register(2) system call. The arguments passed in must
be an array of __s32 holding file descriptors, and nr_args should hold
the number of file descriptors the application wishes to pin for the
duration of the io_uring context (or until IORING_UNREGISTER_FILES is
called).

When used, the application must set IOSQE_FIXED_FILE in the sqe->flags
member. Then, instead of setting sqe->fd to the real fd, it sets sqe->fd
to the index in the array passed in to IORING_REGISTER_FILES.

Files are automatically unregistered when the io_uring context is
torn down. An application need only unregister if it wishes to
register a few set of fds.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c                 | 125 +++++++++++++++++++++++++++++-----
 include/uapi/linux/io_uring.h |   9 ++-
 2 files changed, 116 insertions(+), 18 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 63ad09e7cdc7..86add82e1008 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -100,6 +100,10 @@ struct io_ring_ctx {
 		struct fasync_struct	*cq_fasync;
 	} ____cacheline_aligned_in_smp;
 
+	/* if used, fixed file set */
+	struct file		**user_files;
+	unsigned		nr_user_files;
+
 	/* if used, fixed mapped user buffers */
 	unsigned		nr_user_bufs;
 	struct io_mapped_ubuf	*user_bufs;
@@ -137,6 +141,7 @@ struct io_kiocb {
 #define REQ_F_FORCE_NONBLOCK	1	/* inline submission attempt */
 #define REQ_F_IOPOLL_COMPLETED	2	/* polled IO has completed */
 #define REQ_F_IOPOLL_EAGAIN	4	/* submission got EAGAIN */
+#define REQ_F_FIXED_FILE	8	/* ctx owns file */
 	u64			user_data;
 	u64			res;
 
@@ -359,15 +364,17 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
 		 * Batched puts of the same file, to avoid dirtying the
 		 * file usage count multiple times, if avoidable.
 		 */
-		if (!file) {
-			file = req->rw.ki_filp;
-			file_count = 1;
-		} else if (file == req->rw.ki_filp) {
-			file_count++;
-		} else {
-			fput_many(file, file_count);
-			file = req->rw.ki_filp;
-			file_count = 1;
+		if (!(req->flags & REQ_F_FIXED_FILE)) {
+			if (!file) {
+				file = req->rw.ki_filp;
+				file_count = 1;
+			} else if (file == req->rw.ki_filp) {
+				file_count++;
+			} else {
+				fput_many(file, file_count);
+				file = req->rw.ki_filp;
+				file_count = 1;
+			}
 		}
 
 		if (to_free == ARRAY_SIZE(reqs))
@@ -504,13 +511,19 @@ static void kiocb_end_write(struct kiocb *kiocb)
 	}
 }
 
+static void io_fput(struct io_kiocb *req)
+{
+	if (!(req->flags & REQ_F_FIXED_FILE))
+		fput(req->rw.ki_filp);
+}
+
 static void io_complete_rw(struct kiocb *kiocb, long res, long res2)
 {
 	struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw);
 
 	kiocb_end_write(kiocb);
 
-	fput(kiocb->ki_filp);
+	io_fput(req);
 	io_cqring_add_event(req->ctx, req->user_data, res, 0);
 	io_free_req(req);
 }
@@ -614,7 +627,14 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	struct kiocb *kiocb = &req->rw;
 	int ret;
 
-	kiocb->ki_filp = io_file_get(state, sqe->fd);
+	if (sqe->flags & IOSQE_FIXED_FILE) {
+		if (unlikely(!ctx->user_files || sqe->fd >= ctx->nr_user_files))
+			return -EBADF;
+		kiocb->ki_filp = ctx->user_files[sqe->fd];
+		req->flags |= REQ_F_FIXED_FILE;
+	} else {
+		kiocb->ki_filp = io_file_get(state, sqe->fd);
+	}
 	if (unlikely(!kiocb->ki_filp))
 		return -EBADF;
 	kiocb->ki_pos = sqe->off;
@@ -653,7 +673,8 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	}
 	return 0;
 out_fput:
-	io_file_put(state, kiocb->ki_filp);
+	if (!(sqe->flags & IOSQE_FIXED_FILE))
+		io_file_put(state, kiocb->ki_filp);
 	return ret;
 }
 
@@ -770,7 +791,7 @@ static ssize_t io_read(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	kfree(iovec);
 out_fput:
 	if (unlikely(ret))
-		fput(file);
+		io_fput(req);
 	return ret;
 }
 
@@ -825,7 +846,7 @@ static ssize_t io_write(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	kfree(iovec);
 out_fput:
 	if (unlikely(ret))
-		fput(file);
+		io_fput(req);
 	return ret;
 }
 
@@ -863,14 +884,23 @@ static int io_fsync(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	if (unlikely(sqe->fsync_flags & ~IORING_FSYNC_DATASYNC))
 		return -EINVAL;
 
-	file = fget(sqe->fd);
+	if (sqe->flags & IOSQE_FIXED_FILE) {
+		if (unlikely(!ctx->user_files || sqe->fd >= ctx->nr_user_files))
+			return -EBADF;
+		file = ctx->user_files[sqe->fd];
+	} else {
+		file = fget(sqe->fd);
+	}
+
 	if (unlikely(!file))
 		return -EBADF;
 
 	ret = vfs_fsync_range(file, sqe->off, end > 0 ? end : LLONG_MAX,
 			sqe->fsync_flags & IORING_FSYNC_DATASYNC);
 
-	fput(file);
+	if (!(sqe->flags & IOSQE_FIXED_FILE))
+		fput(file);
+
 	io_cqring_add_event(ctx, sqe->user_data, ret, 0);
 	io_free_req(req);
 	return 0;
@@ -988,7 +1018,7 @@ static int io_submit_sqe(struct io_ring_ctx *ctx, struct sqe_submit *s,
 	ssize_t ret;
 
 	/* enforce forwards compatibility on users */
-	if (unlikely(s->sqe->flags))
+	if (unlikely(s->sqe->flags & ~IOSQE_FIXED_FILE))
 		return -EINVAL;
 
 	req = io_get_req(ctx, state);
@@ -1173,6 +1203,57 @@ static int __io_uring_enter(struct io_ring_ctx *ctx, unsigned to_submit,
 	return ret;
 }
 
+static int io_sqe_files_unregister(struct io_ring_ctx *ctx)
+{
+	int i;
+
+	if (!ctx->user_files)
+		return -ENXIO;
+
+	for (i = 0; i < ctx->nr_user_files; i++)
+		fput(ctx->user_files[i]);
+
+	kfree(ctx->user_files);
+	ctx->user_files = NULL;
+	ctx->nr_user_files = 0;
+	return 0;
+}
+
+static int io_sqe_files_register(struct io_ring_ctx *ctx, void __user *arg,
+				 unsigned nr_args)
+{
+	__s32 __user *fds = (__s32 __user *) arg;
+	int fd, i, ret = 0;
+
+	if (ctx->user_files)
+		return -EBUSY;
+	if (!nr_args)
+		return -EINVAL;
+
+	ctx->user_files = kcalloc(nr_args, sizeof(struct file *), GFP_KERNEL);
+	if (!ctx->user_files)
+		return -ENOMEM;
+
+	for (i = 0; i < nr_args; i++) {
+		ret = -EFAULT;
+		if (copy_from_user(&fd, &fds[i], sizeof(fd)))
+			break;
+
+		ctx->user_files[i] = fget(fd);
+
+		ret = -EBADF;
+		if (!ctx->user_files[i])
+			break;
+		ctx->nr_user_files++;
+		ret = 0;
+	}
+
+	if (ret)
+		io_sqe_files_unregister(ctx);
+
+	return ret;
+}
+
 static int io_sq_offload_start(struct io_ring_ctx *ctx)
 {
 	int ret;
@@ -1468,6 +1549,7 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx)
 	io_sq_offload_stop(ctx);
 	io_iopoll_reap_events(ctx);
 	io_free_scq_urings(ctx);
+	io_sqe_files_unregister(ctx);
 	io_sqe_buffer_unregister(ctx);
 	percpu_ref_exit(&ctx->refs);
 	io_unaccount_mem(ctx, ring_pages(ctx->sq_entries, ctx->cq_entries));
@@ -1780,6 +1862,15 @@ static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
 			break;
 		ret = io_sqe_buffer_unregister(ctx);
 		break;
+	case IORING_REGISTER_FILES:
+		ret = io_sqe_files_register(ctx, arg, nr_args);
+		break;
+	case IORING_UNREGISTER_FILES:
+		ret = -EINVAL;
+		if (arg || nr_args)
+			break;
+		ret = io_sqe_files_unregister(ctx);
+		break;
 	default:
 		ret = -EINVAL;
 		break;
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 03ce7133c3b2..8323320077ec 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -18,7 +18,7 @@
  */
 struct io_uring_sqe {
 	__u8	opcode;		/* type of operation for this sqe */
-	__u8	flags;		/* as of now unused */
+	__u8	flags;		/* IOSQE_ flags */
 	__u16	ioprio;		/* ioprio for the request */
 	__s32	fd;		/* file descriptor to do IO on */
 	__u64	off;		/* offset into file */
@@ -35,6 +35,11 @@ struct io_uring_sqe {
 	};
 };
 
+/*
+ * sqe->flags
+ */
+#define IOSQE_FIXED_FILE	(1 << 0)	/* use fixed fileset */
+
 /*
  * io_uring_setup() flags
  */
@@ -114,5 +119,7 @@ struct io_uring_params {
  */
 #define IORING_REGISTER_BUFFERS		0
 #define IORING_UNREGISTER_BUFFERS	1
+#define IORING_REGISTER_FILES		2
+#define IORING_UNREGISTER_FILES		3
 
 #endif
-- 
2.17.1

[PATCH 09/13] io_uring: add submission polling

[Jens Axboe]

This enables an application to do IO, without ever entering the kernel.
By using the SQ ring to fill in new sqes and watching for completions
on the CQ ring, we can submit and reap IOs without doing a single system
call. The kernel side thread will poll for new submissions, and in case
of HIPRI/polled IO, it'll also poll for completions.

Proof of concept. If the thread has been idle for 1 second, it will set
sq_ring->flags |= IORING_SQ_NEED_WAKEUP. The application will have to
call io_uring_enter() to start things back up again. If IO is kept busy,
that will never be needed. Basically an application that has this
feature enabled will guard it's io_uring_enter(2) call with:

read_barrier();
if (*sq_ring->flags & IORING_SQ_NEED_WAKEUP)
	io_uring_enter(fd, to_submit, 0, 0);

instead of calling it unconditionally.

Improvements:

1) Maybe have smarter backoff. Busy loop for X time, then go to
   monitor/mwait, finally the schedule we have now after an idle
   second. Might not be worth the complexity.

2) Probably want the application to pass in the appropriate grace
   period, not hard code it at 1 second.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c                 | 219 +++++++++++++++++++++++++++++++++-
 include/uapi/linux/io_uring.h |  10 +-
 2 files changed, 222 insertions(+), 7 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 86add82e1008..2deda7b1b3dd 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -24,6 +24,7 @@
 #include <linux/percpu.h>
 #include <linux/slab.h>
 #include <linux/workqueue.h>
+#include <linux/kthread.h>
 #include <linux/blkdev.h>
 #include <linux/bvec.h>
 #include <linux/anon_inodes.h>
@@ -87,8 +88,10 @@ struct io_ring_ctx {
 
 	/* IO offload */
 	struct workqueue_struct	*sqo_wq;
+	struct task_struct	*sqo_thread;	/* if using sq thread polling */
 	struct mm_struct	*sqo_mm;
 	struct files_struct	*sqo_files;
+	wait_queue_head_t	sqo_wait;
 
 	struct {
 		/* CQ ring */
@@ -264,6 +267,9 @@ static void __io_cqring_add_event(struct io_ring_ctx *ctx, u64 ki_user_data,
 
 	if (waitqueue_active(&ctx->wait))
 		wake_up(&ctx->wait);
+	if ((ctx->flags & IORING_SETUP_SQPOLL) &&
+	    waitqueue_active(&ctx->sqo_wait))
+		wake_up(&ctx->sqo_wait);
 }
 
 static void io_cqring_add_event(struct io_ring_ctx *ctx, u64 ki_user_data,
@@ -1106,6 +1112,168 @@ static bool io_get_sqring(struct io_ring_ctx *ctx, struct sqe_submit *s)
 	return false;
 }
 
+static int io_submit_sqes(struct io_ring_ctx *ctx, struct sqe_submit *sqes,
+			  unsigned int nr, bool mm_fault)
+{
+	struct io_submit_state state, *statep = NULL;
+	int ret, i, submitted = 0;
+
+	if (nr > IO_PLUG_THRESHOLD) {
+		io_submit_state_start(&state, ctx, nr);
+		statep = &state;
+	}
+
+	for (i = 0; i < nr; i++) {
+		if (unlikely(mm_fault))
+			ret = -EFAULT;
+		else
+			ret = io_submit_sqe(ctx, &sqes[i], statep);
+		if (!ret) {
+			submitted++;
+			continue;
+		}
+
+		io_cqring_add_event(ctx, sqes[i].sqe->user_data, ret, 0);
+	}
+
+	if (statep)
+		io_submit_state_end(&state);
+
+	return submitted;
+}
+
+static int io_sq_thread(void *data)
+{
+	struct sqe_submit sqes[IO_IOPOLL_BATCH];
+	struct io_ring_ctx *ctx = data;
+	struct mm_struct *cur_mm = NULL;
+	struct files_struct *old_files;
+	mm_segment_t old_fs;
+	DEFINE_WAIT(wait);
+	unsigned inflight;
+	unsigned long timeout;
+
+	old_files = current->files;
+	current->files = ctx->sqo_files;
+
+	old_fs = get_fs();
+	set_fs(USER_DS);
+
+	timeout = inflight = 0;
+	while (!kthread_should_stop()) {
+		bool all_fixed, mm_fault = false;
+		int i;
+
+		if (inflight) {
+			unsigned int nr_events = 0;
+
+			/*
+			 * Normal IO, just pretend everything completed.
+			 * We don't have to poll completions for that.
+			 */
+			if (ctx->flags & IORING_SETUP_IOPOLL) {
+				/*
+				 * App should not use IORING_ENTER_GETEVENTS
+				 * with thread polling, but if it does, then
+				 * ensure we are mutually exclusive.
+				 */
+				if (mutex_trylock(&ctx->uring_lock)) {
+					io_iopoll_check(ctx, &nr_events, 0);
+					mutex_unlock(&ctx->uring_lock);
+				}
+			} else {
+				nr_events = inflight;
+			}
+
+			inflight -= nr_events;
+			if (!inflight)
+				timeout = jiffies + HZ;
+		}
+
+		if (!io_get_sqring(ctx, &sqes[0])) {
+			/*
+			 * We're polling, let us spin for a second without
+			 * work before going to sleep.
+			 */
+			if (inflight || !time_after(jiffies, timeout)) {
+				cpu_relax();
+				continue;
+			}
+
+			/*
+			 * Drop cur_mm before scheduling, we can't hold it for
+			 * long periods (or over schedule()). Do this before
+			 * adding ourselves to the waitqueue, as the unuse/drop
+			 * may sleep.
+			 */
+			if (cur_mm) {
+				unuse_mm(cur_mm);
+				mmput(cur_mm);
+				cur_mm = NULL;
+			}
+
+			prepare_to_wait(&ctx->sqo_wait, &wait,
+						TASK_INTERRUPTIBLE);
+
+			/* Tell userspace we may need a wakeup call */
+			ctx->sq_ring->flags |= IORING_SQ_NEED_WAKEUP;
+			smp_wmb();
+
+			if (!io_get_sqring(ctx, &sqes[0])) {
+				if (kthread_should_park())
+					kthread_parkme();
+				if (kthread_should_stop()) {
+					finish_wait(&ctx->sqo_wait, &wait);
+					break;
+				}
+				if (signal_pending(current))
+					flush_signals(current);
+				schedule();
+				finish_wait(&ctx->sqo_wait, &wait);
+
+				ctx->sq_ring->flags &= ~IORING_SQ_NEED_WAKEUP;
+				smp_wmb();
+				continue;
+			}
+			finish_wait(&ctx->sqo_wait, &wait);
+
+			ctx->sq_ring->flags &= ~IORING_SQ_NEED_WAKEUP;
+			smp_wmb();
+		}
+
+		i = 0;
+		all_fixed = true;
+		do {
+			if (all_fixed && io_sqe_needs_user(sqes[i].sqe))
+				all_fixed = false;
+
+			i++;
+			if (i == ARRAY_SIZE(sqes))
+				break;
+		} while (io_get_sqring(ctx, &sqes[i]));
+
+		io_commit_sqring(ctx);
+
+		/* Unless all new commands are FIXED regions, grab mm */
+		if (!all_fixed && !cur_mm) {
+			mm_fault = !mmget_not_zero(ctx->sqo_mm);
+			if (!mm_fault) {
+				use_mm(ctx->sqo_mm);
+				cur_mm = ctx->sqo_mm;
+			}
+		}
+
+		inflight += io_submit_sqes(ctx, sqes, i, mm_fault);
+	}
+	current->files = old_files;
+	set_fs(old_fs);
+	if (cur_mm) {
+		unuse_mm(cur_mm);
+		mmput(cur_mm);
+	}
+	return 0;
+}
+
 static int io_ring_submit(struct io_ring_ctx *ctx, unsigned int to_submit)
 {
 	struct io_submit_state state, *statep = NULL;
@@ -1179,9 +1347,14 @@ static int __io_uring_enter(struct io_ring_ctx *ctx, unsigned to_submit,
 	int ret = 0;
 
 	if (to_submit) {
-		ret = io_ring_submit(ctx, to_submit);
-		if (ret < 0)
-			return ret;
+		if (ctx->flags & IORING_SETUP_SQPOLL) {
+			wake_up(&ctx->sqo_wait);
+			ret = to_submit;
+		} else {
+			ret = io_ring_submit(ctx, to_submit);
+			if (ret < 0)
+				return ret;
+		}
 	}
 	if (flags & IORING_ENTER_GETEVENTS) {
 		unsigned nr_events = 0;
@@ -1254,10 +1427,12 @@ static int io_sqe_files_register(struct io_ring_ctx *ctx, void __user *arg,
 	return ret;
 }
 
-static int io_sq_offload_start(struct io_ring_ctx *ctx)
+static int io_sq_offload_start(struct io_ring_ctx *ctx,
+			       struct io_uring_params *p)
 {
 	int ret;
 
+	init_waitqueue_head(&ctx->sqo_wait);
 	ctx->sqo_mm = current->mm;
 
 	/*
@@ -1270,6 +1445,27 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx)
 	if (!ctx->sqo_files)
 		goto err;
 
+	if (ctx->flags & IORING_SETUP_SQPOLL) {
+		if (p->flags & IORING_SETUP_SQ_AFF) {
+			ctx->sqo_thread = kthread_create_on_cpu(io_sq_thread,
+							ctx, p->sq_thread_cpu,
+							"io_uring-sq");
+		} else {
+			ctx->sqo_thread = kthread_create(io_sq_thread, ctx,
+							"io_uring-sq");
+		}
+		if (IS_ERR(ctx->sqo_thread)) {
+			ret = PTR_ERR(ctx->sqo_thread);
+			ctx->sqo_thread = NULL;
+			goto err;
+		}
+		wake_up_process(ctx->sqo_thread);
+	} else if (p->flags & IORING_SETUP_SQ_AFF) {
+		/* Can't have SQ_AFF without SQPOLL */
+		ret = -EINVAL;
+		goto err;
+	}
+
 	/* Do QD, or 2 * CPUS, whatever is smallest */
 	ctx->sqo_wq = alloc_workqueue("io_ring-wq", WQ_UNBOUND | WQ_FREEZABLE,
 			min(ctx->sq_entries - 1, 2 * num_online_cpus()));
@@ -1280,6 +1476,11 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx)
 
 	return 0;
 err:
+	if (ctx->sqo_thread) {
+		kthread_park(ctx->sqo_thread);
+		kthread_stop(ctx->sqo_thread);
+		ctx->sqo_thread = NULL;
+	}
 	if (ctx->sqo_files)
 		ctx->sqo_files = NULL;
 	ctx->sqo_mm = NULL;
@@ -1288,6 +1489,11 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx)
 
 static void io_sq_offload_stop(struct io_ring_ctx *ctx)
 {
+	if (ctx->sqo_thread) {
+		kthread_park(ctx->sqo_thread);
+		kthread_stop(ctx->sqo_thread);
+		ctx->sqo_thread = NULL;
+	}
 	if (ctx->sqo_wq) {
 		destroy_workqueue(ctx->sqo_wq);
 		ctx->sqo_wq = NULL;
@@ -1780,7 +1986,7 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p,
 	if (ret)
 		goto err;
 
-	ret = io_sq_offload_start(ctx);
+	ret = io_sq_offload_start(ctx, p);
 	if (ret)
 		goto err;
 
@@ -1815,7 +2021,8 @@ static long io_uring_setup(u32 entries, struct io_uring_params __user *params,
 			return -EINVAL;
 	}
 
-	if (p.flags & ~IORING_SETUP_IOPOLL)
+	if (p.flags & ~(IORING_SETUP_IOPOLL | IORING_SETUP_SQPOLL |
+			IORING_SETUP_SQ_AFF))
 		return -EINVAL;
 
 	ret = io_uring_create(entries, &p, compat);
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 8323320077ec..37c7402be9ca 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -44,6 +44,8 @@ struct io_uring_sqe {
  * io_uring_setup() flags
  */
 #define IORING_SETUP_IOPOLL	(1 << 0)	/* io_context is polled */
+#define IORING_SETUP_SQPOLL	(1 << 1)	/* SQ poll thread */
+#define IORING_SETUP_SQ_AFF	(1 << 2)	/* sq_thread_cpu is valid */
 
 #define IORING_OP_NOP		0
 #define IORING_OP_READV		1
@@ -87,6 +89,11 @@ struct io_sqring_offsets {
 	__u32 resv[3];
 };
 
+/*
+ * sq_ring->flags
+ */
+#define IORING_SQ_NEED_WAKEUP	(1 << 0) /* needs io_uring_enter wakeup */
+
 struct io_cqring_offsets {
 	__u32 head;
 	__u32 tail;
@@ -109,7 +116,8 @@ struct io_uring_params {
 	__u32 sq_entries;
 	__u32 cq_entries;
 	__u32 flags;
-	__u16 resv[10];
+	__u16 sq_thread_cpu;
+	__u16 resv[9];
 	struct io_sqring_offsets sq_off;
 	struct io_cqring_offsets cq_off;
 };
-- 
2.17.1

Re: [PATCH 09/13] io_uring: add submission polling

[Christoph Hellwig]

On Wed, Jan 23, 2019 at 08:35:22AM -0700, Jens Axboe wrote:
> Proof of concept.

Is that still true?

> 1) Maybe have smarter backoff. Busy loop for X time, then go to
>    monitor/mwait, finally the schedule we have now after an idle
>    second. Might not be worth the complexity.
> 
> 2) Probably want the application to pass in the appropriate grace
>    period, not hard code it at 1 second.

2) actually sounds really useful.  Should we look into it ASAP?

>  
>  	struct {
>  		/* CQ ring */
> @@ -264,6 +267,9 @@ static void __io_cqring_add_event(struct io_ring_ctx *ctx, u64 ki_user_data,
>  
>  	if (waitqueue_active(&ctx->wait))
>  		wake_up(&ctx->wait);
> +	if ((ctx->flags & IORING_SETUP_SQPOLL) &&
> +	    waitqueue_active(&ctx->sqo_wait))

waitqueue_active is really cheap and sqo_wait should not otherwise
by active.  Do we really need the flags check here?

> +			/*
> +			 * Normal IO, just pretend everything completed.
> +			 * We don't have to poll completions for that.
> +			 */
> +			if (ctx->flags & IORING_SETUP_IOPOLL) {
> +				/*
> +				 * App should not use IORING_ENTER_GETEVENTS
> +				 * with thread polling, but if it does, then
> +				 * ensure we are mutually exclusive.

Should we just return an error early on in this case instead?

>  	if (to_submit) {
> +		if (ctx->flags & IORING_SETUP_SQPOLL) {
> +			wake_up(&ctx->sqo_wait);
> +			ret = to_submit;

Do these semantics really make sense?  Maybe we should have an
IORING_ENTER_WAKE_SQ instead of overloading the to_submit argument?
Especially as we don't really care about returning the number passed in.

> +	if (ctx->sqo_thread) {
> +		kthread_park(ctx->sqo_thread);

Can you explain why we need the whole kthread_park game?  It is only
intended to deal with pausing a thread, and if need it to shut down
a thread we have a bug somewhere.

>  static void io_sq_offload_stop(struct io_ring_ctx *ctx)
>  {
> +	if (ctx->sqo_thread) {
> +		kthread_park(ctx->sqo_thread);
> +		kthread_stop(ctx->sqo_thread);
> +		ctx->sqo_thread = NULL;

Also there isn't really much of a point in setting pointers to NULL
just before freeing the containing structure.  In the best case this
now papers over bugs that poisoning or kasan would otherwise find.

Re: [PATCH 09/13] io_uring: add submission polling

[Jens Axboe]

On 1/28/19 8:09 AM, Christoph Hellwig wrote:
> On Wed, Jan 23, 2019 at 08:35:22AM -0700, Jens Axboe wrote:
>> Proof of concept.
> 
> Is that still true?

I guess I can remove it now, dates back to when it was initially just
a test. But it should be solid, I'll kill that part.

>> 1) Maybe have smarter backoff. Busy loop for X time, then go to
>>    monitor/mwait, finally the schedule we have now after an idle
>>    second. Might not be worth the complexity.
>>
>> 2) Probably want the application to pass in the appropriate grace
>>    period, not hard code it at 1 second.
> 
> 2) actually sounds really useful.  Should we look into it ASAP?

I think so. Question is what kind of granularity we need for this. I
think we can go pretty coarse and keep it in msec, using a short to
pass this in like we do for the thread CPU. That gives us 0..65535 msec,
which should be plenty of range.

>>  	struct {
>>  		/* CQ ring */
>> @@ -264,6 +267,9 @@ static void __io_cqring_add_event(struct io_ring_ctx *ctx, u64 ki_user_data,
>>  
>>  	if (waitqueue_active(&ctx->wait))
>>  		wake_up(&ctx->wait);
>> +	if ((ctx->flags & IORING_SETUP_SQPOLL) &&
>> +	    waitqueue_active(&ctx->sqo_wait))
> 
> waitqueue_active is really cheap and sqo_wait should not otherwise
> by active.  Do we really need the flags check here?

Probably not, I'll kill it.

>> +			/*
>> +			 * Normal IO, just pretend everything completed.
>> +			 * We don't have to poll completions for that.
>> +			 */
>> +			if (ctx->flags & IORING_SETUP_IOPOLL) {
>> +				/*
>> +				 * App should not use IORING_ENTER_GETEVENTS
>> +				 * with thread polling, but if it does, then
>> +				 * ensure we are mutually exclusive.
> 
> Should we just return an error early on in this case instead?

I think that'd make it awkward, since it's out-of-line. If the app is doing
things it shouldn't in this case, its own io_uring_enter() would most likely
fail occasionally with -EBUSY anyway.

>>  	if (to_submit) {
>> +		if (ctx->flags & IORING_SETUP_SQPOLL) {
>> +			wake_up(&ctx->sqo_wait);
>> +			ret = to_submit;
> 
> Do these semantics really make sense?  Maybe we should have an
> IORING_ENTER_WAKE_SQ instead of overloading the to_submit argument?
> Especially as we don't really care about returning the number passed in.

I like that change, I'll add IORING_ENTER_SQ_WAKEUP instead of using
'to_submit' for this. We can't validate the number anyway.

>> +	if (ctx->sqo_thread) {
>> +		kthread_park(ctx->sqo_thread);
> 
> Can you explain why we need the whole kthread_park game?  It is only
> intended to deal with pausing a thread, and if need it to shut down
> a thread we have a bug somewhere.

It is working around a bug in shutting down a thread that is affinitized
to a single CPU, I just didn't want to deal with hunting that down right
now.

>>  static void io_sq_offload_stop(struct io_ring_ctx *ctx)
>>  {
>> +	if (ctx->sqo_thread) {
>> +		kthread_park(ctx->sqo_thread);
>> +		kthread_stop(ctx->sqo_thread);
>> +		ctx->sqo_thread = NULL;
> 
> Also there isn't really much of a point in setting pointers to NULL
> just before freeing the containing structure.  In the best case this
> now papers over bugs that poisoning or kasan would otherwise find.

Removed.

-- 
Jens Axboe

Re: [PATCH 09/13] io_uring: add submission polling

[Christoph Hellwig]

On Mon, Jan 28, 2019 at 10:05:37AM -0700, Jens Axboe wrote:
> >> 2) Probably want the application to pass in the appropriate grace
> >>    period, not hard code it at 1 second.
> > 
> > 2) actually sounds really useful.  Should we look into it ASAP?
> 
> I think so. Question is what kind of granularity we need for this. I
> think we can go pretty coarse and keep it in msec, using a short to
> pass this in like we do for the thread CPU. That gives us 0..65535 msec,
> which should be plenty of range.

msec granualarity sounds fine.  But is it really worth using a short
instead of a 32-bit value these days?

Also 16385 seems very limiting for a cpu value, especially as our
normal cpu ids are ints.

Re: [PATCH 09/13] io_uring: add submission polling

[Jens Axboe]

On 1/28/19 11:29 PM, Christoph Hellwig wrote:
> On Mon, Jan 28, 2019 at 10:05:37AM -0700, Jens Axboe wrote:
>>>> 2) Probably want the application to pass in the appropriate grace
>>>>    period, not hard code it at 1 second.
>>>
>>> 2) actually sounds really useful.  Should we look into it ASAP?
>>
>> I think so. Question is what kind of granularity we need for this. I
>> think we can go pretty coarse and keep it in msec, using a short to
>> pass this in like we do for the thread CPU. That gives us 0..65535 msec,
>> which should be plenty of range.
> 
> msec granualarity sounds fine.  But is it really worth using a short
> instead of a 32-bit value these days?
> 
> Also 16385 seems very limiting for a cpu value, especially as our
> normal cpu ids are ints.

I'll bump them both to 4-bytes.

-- 
Jens Axboe

Re: [PATCH 09/13] io_uring: add submission polling

[Jeff Moyer]

Jens Axboe <axboe@kernel.dk> writes:

> @@ -1270,6 +1445,27 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx)
>  	if (!ctx->sqo_files)
>  		goto err;
>  
> +	if (ctx->flags & IORING_SETUP_SQPOLL) {
> +		if (p->flags & IORING_SETUP_SQ_AFF) {
> +			ctx->sqo_thread = kthread_create_on_cpu(io_sq_thread,
> +							ctx, p->sq_thread_cpu,
> +							"io_uring-sq");

sq_thread_cpu looks like another candidate for array_index_nospec.
Following the macros, kthread_create_on_cpu calls cpu_to_node, which
does:
        return per_cpu(x86_cpu_to_node_map, cpu);

#define per_cpu(var, cpu)       (*per_cpu_ptr(&(var), cpu))
#define per_cpu_ptr(ptr, cpu)                                           \
({                                                                      \
        __verify_pcpu_ptr(ptr);                                         \
        SHIFT_PERCPU_PTR((ptr), per_cpu_offset((cpu)));                 \
})
#define per_cpu_offset(x) (__per_cpu_offset[x])
                           ^^^^^^^^^^^^^^^^^^^

It also looks like there's no bounds checking there, so we probably want
to make sure sq_thread_cpu can't overflow the __per_cpu_offset array
(NR_CPUS).

-Jeff

Re: [PATCH 09/13] io_uring: add submission polling

[Jens Axboe]

On 1/28/19 2:13 PM, Jeff Moyer wrote:
> Jens Axboe <axboe@kernel.dk> writes:
> 
>> @@ -1270,6 +1445,27 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx)
>>  	if (!ctx->sqo_files)
>>  		goto err;
>>  
>> +	if (ctx->flags & IORING_SETUP_SQPOLL) {
>> +		if (p->flags & IORING_SETUP_SQ_AFF) {
>> +			ctx->sqo_thread = kthread_create_on_cpu(io_sq_thread,
>> +							ctx, p->sq_thread_cpu,
>> +							"io_uring-sq");
> 
> sq_thread_cpu looks like another candidate for array_index_nospec.
> Following the macros, kthread_create_on_cpu calls cpu_to_node, which
> does:
>         return per_cpu(x86_cpu_to_node_map, cpu);
> 
> #define per_cpu(var, cpu)       (*per_cpu_ptr(&(var), cpu))
> #define per_cpu_ptr(ptr, cpu)                                           \
> ({                                                                      \
>         __verify_pcpu_ptr(ptr);                                         \
>         SHIFT_PERCPU_PTR((ptr), per_cpu_offset((cpu)));                 \
> })
> #define per_cpu_offset(x) (__per_cpu_offset[x])
>                            ^^^^^^^^^^^^^^^^^^^
> 
> It also looks like there's no bounds checking there, so we probably want
> to make sure sq_thread_cpu can't overflow the __per_cpu_offset array
> (NR_CPUS).

Added, can't hurt in any case.

-- 
Jens Axboe

[PATCH 09/18] io_uring: use fget/fput_many() for file references

[Jens Axboe]

Add a separate io_submit_state structure, to cache some of the things
we need for IO submission.

One such example is file reference batching. io_submit_state. We get as
many references as the number of sqes we are submitting, and drop
unused ones if we end up switching files. The assumption here is that
we're usually only dealing with one fd, and if there are multiple,
hopefuly they are at least somewhat ordered. Could trivially be extended
to cover multiple fds, if needed.

On the completion side we do the same thing, except this is trivially
done just locally in io_iopoll_reap().

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c | 139 ++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 118 insertions(+), 21 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index f17c2dc73e40..e9c237d471ae 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -132,6 +132,19 @@ struct io_kiocb {
 #define IO_PLUG_THRESHOLD		2
 #define IO_IOPOLL_BATCH			8
 
+struct io_submit_state {
+	struct blk_plug plug;
+
+	/*
+	 * File reference cache
+	 */
+	struct file *file;
+	unsigned int fd;
+	unsigned int has_refs;
+	unsigned int used_refs;
+	unsigned int ios_left;
+};
+
 static struct kmem_cache *req_cachep;
 
 static const struct file_operations io_uring_fops;
@@ -285,9 +298,11 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
 			       struct list_head *done)
 {
 	void *reqs[IO_IOPOLL_BATCH];
+	int file_count, to_free;
+	struct file *file = NULL;
 	struct io_kiocb *req;
-	int to_free = 0;
 
+	file_count = to_free = 0;
 	while (!list_empty(done)) {
 		req = list_first_entry(done, struct io_kiocb, list);
 		list_del(&req->list);
@@ -297,12 +312,28 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
 		reqs[to_free++] = req;
 		(*nr_events)++;
 
-		fput(req->rw.ki_filp);
+		/*
+		 * Batched puts of the same file, to avoid dirtying the
+		 * file usage count multiple times, if avoidable.
+		 */
+		if (!file) {
+			file = req->rw.ki_filp;
+			file_count = 1;
+		} else if (file == req->rw.ki_filp) {
+			file_count++;
+		} else {
+			fput_many(file, file_count);
+			file = req->rw.ki_filp;
+			file_count = 1;
+		}
+
 		if (to_free == ARRAY_SIZE(reqs))
 			io_free_req_many(ctx, reqs, &to_free);
 	}
 	io_commit_cqring(ctx);
 
+	if (file)
+		fput_many(file, file_count);
 	if (to_free)
 		io_free_req_many(ctx, reqs, &to_free);
 }
@@ -491,14 +522,56 @@ static void io_iopoll_req_issued(struct io_kiocb *req)
 		list_add_tail(&req->list, &ctx->poll_list);
 }
 
+static void io_file_put(struct io_submit_state *state, struct file *file)
+{
+	if (!state) {
+		fput(file);
+	} else if (state->file) {
+		int diff = state->has_refs - state->used_refs;
+
+		if (diff)
+			fput_many(state->file, diff);
+		state->file = NULL;
+	}
+}
+
+/*
+ * Get as many references to a file as we have IOs left in this submission,
+ * assuming most submissions are for one file, or at least that each file
+ * has more than one submission.
+ */
+static struct file *io_file_get(struct io_submit_state *state, int fd)
+{
+	if (!state)
+		return fget(fd);
+
+	if (state->file) {
+		if (state->fd == fd) {
+			state->used_refs++;
+			state->ios_left--;
+			return state->file;
+		}
+		io_file_put(state, NULL);
+	}
+	state->file = fget_many(fd, state->ios_left);
+	if (!state->file)
+		return NULL;
+
+	state->fd = fd;
+	state->has_refs = state->ios_left;
+	state->used_refs = 1;
+	state->ios_left--;
+	return state->file;
+}
+
 static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
-		      bool force_nonblock)
+		      bool force_nonblock, struct io_submit_state *state)
 {
 	struct io_ring_ctx *ctx = req->ctx;
 	struct kiocb *kiocb = &req->rw;
 	int ret;
 
-	kiocb->ki_filp = fget(sqe->fd);
+	kiocb->ki_filp = io_file_get(state, sqe->fd);
 	if (unlikely(!kiocb->ki_filp))
 		return -EBADF;
 	kiocb->ki_pos = sqe->off;
@@ -537,7 +610,7 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	}
 	return 0;
 out_fput:
-	fput(kiocb->ki_filp);
+	io_file_put(state, kiocb->ki_filp);
 	return ret;
 }
 
@@ -577,7 +650,7 @@ static int io_import_iovec(struct io_ring_ctx *ctx, int rw,
 }
 
 static ssize_t io_read(struct io_kiocb *req, const struct io_uring_sqe *sqe,
-		       bool force_nonblock)
+		       bool force_nonblock, struct io_submit_state *state)
 {
 	struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
 	struct kiocb *kiocb = &req->rw;
@@ -585,7 +658,7 @@ static ssize_t io_read(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	struct file *file;
 	ssize_t ret;
 
-	ret = io_prep_rw(req, sqe, force_nonblock);
+	ret = io_prep_rw(req, sqe, force_nonblock, state);
 	if (ret)
 		return ret;
 	file = kiocb->ki_filp;
@@ -620,7 +693,7 @@ static ssize_t io_read(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 }
 
 static ssize_t io_write(struct io_kiocb *req, const struct io_uring_sqe *sqe,
-			bool force_nonblock)
+			bool force_nonblock, struct io_submit_state *state)
 {
 	struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
 	struct kiocb *kiocb = &req->rw;
@@ -628,7 +701,7 @@ static ssize_t io_write(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	struct file *file;
 	ssize_t ret;
 
-	ret = io_prep_rw(req, sqe, force_nonblock);
+	ret = io_prep_rw(req, sqe, force_nonblock, state);
 	if (ret)
 		return ret;
 	file = kiocb->ki_filp;
@@ -722,7 +795,8 @@ static int io_fsync(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 }
 
 static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
-			   struct sqe_submit *s, bool force_nonblock)
+			   struct sqe_submit *s, bool force_nonblock,
+			   struct io_submit_state *state)
 {
 	const struct io_uring_sqe *sqe = s->sqe;
 	ssize_t ret;
@@ -737,10 +811,10 @@ static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 		ret = io_nop(req, sqe);
 		break;
 	case IORING_OP_READV:
-		ret = io_read(req, sqe, force_nonblock);
+		ret = io_read(req, sqe, force_nonblock, state);
 		break;
 	case IORING_OP_WRITEV:
-		ret = io_write(req, sqe, force_nonblock);
+		ret = io_write(req, sqe, force_nonblock, state);
 		break;
 	case IORING_OP_FSYNC:
 		ret = io_fsync(req, sqe, force_nonblock);
@@ -786,7 +860,7 @@ static void io_sq_wq_submit_work(struct work_struct *work)
 	use_mm(ctx->sqo_mm);
 	set_fs(USER_DS);
 
-	ret = __io_submit_sqe(ctx, req, s, false);
+	ret = __io_submit_sqe(ctx, req, s, false, NULL);
 
 	set_fs(old_fs);
 	unuse_mm(ctx->sqo_mm);
@@ -799,7 +873,8 @@ static void io_sq_wq_submit_work(struct work_struct *work)
 	current->files = old_files;
 }
 
-static int io_submit_sqe(struct io_ring_ctx *ctx, struct sqe_submit *s)
+static int io_submit_sqe(struct io_ring_ctx *ctx, struct sqe_submit *s,
+			 struct io_submit_state *state)
 {
 	struct io_kiocb *req;
 	ssize_t ret;
@@ -812,7 +887,7 @@ static int io_submit_sqe(struct io_ring_ctx *ctx, struct sqe_submit *s)
 	if (unlikely(!req))
 		return -EAGAIN;
 
-	ret = __io_submit_sqe(ctx, req, s, true);
+	ret = __io_submit_sqe(ctx, req, s, true, state);
 	if (ret == -EAGAIN) {
 		memcpy(&req->submit, s, sizeof(*s));
 		INIT_WORK(&req->work, io_sq_wq_submit_work);
@@ -825,6 +900,26 @@ static int io_submit_sqe(struct io_ring_ctx *ctx, struct sqe_submit *s)
 	return ret;
 }
 
+/*
+ * Batched submission is done, ensure local IO is flushed out.
+ */
+static void io_submit_state_end(struct io_submit_state *state)
+{
+	blk_finish_plug(&state->plug);
+	io_file_put(state, NULL);
+}
+
+/*
+ * Start submission side cache.
+ */
+static void io_submit_state_start(struct io_submit_state *state,
+				  struct io_ring_ctx *ctx, unsigned max_ios)
+{
+	blk_start_plug(&state->plug);
+	state->file = NULL;
+	state->ios_left = max_ios;
+}
+
 static void io_commit_sqring(struct io_ring_ctx *ctx)
 {
 	struct io_sq_ring *ring = ctx->sq_ring;
@@ -871,11 +966,13 @@ static bool io_get_sqring(struct io_ring_ctx *ctx, struct sqe_submit *s)
 
 static int io_ring_submit(struct io_ring_ctx *ctx, unsigned int to_submit)
 {
+	struct io_submit_state state, *statep = NULL;
 	int i, ret = 0, submit = 0;
-	struct blk_plug plug;
 
-	if (to_submit > IO_PLUG_THRESHOLD)
-		blk_start_plug(&plug);
+	if (to_submit > IO_PLUG_THRESHOLD) {
+		io_submit_state_start(&state, ctx, to_submit);
+		statep = &state;
+	}
 
 	for (i = 0; i < to_submit; i++) {
 		struct sqe_submit s;
@@ -883,7 +980,7 @@ static int io_ring_submit(struct io_ring_ctx *ctx, unsigned int to_submit)
 		if (!io_get_sqring(ctx, &s))
 			break;
 
-		ret = io_submit_sqe(ctx, &s);
+		ret = io_submit_sqe(ctx, &s, statep);
 		if (ret) {
 			io_drop_sqring(ctx);
 			break;
@@ -893,8 +990,8 @@ static int io_ring_submit(struct io_ring_ctx *ctx, unsigned int to_submit)
 	}
 	io_commit_sqring(ctx);
 
-	if (to_submit > IO_PLUG_THRESHOLD)
-		blk_finish_plug(&plug);
+	if (statep)
+		io_submit_state_end(statep);
 
 	return submit ? submit : ret;
 }
-- 
2.17.1

[PATCH 10/13] io_uring: add io_kiocb ref count

[Jens Axboe]

We'll use this for the POLL implementation. Regular requests will
NOT be using references, so initialize it to 0. Any real use of
the io_kiocb ref will initialize it to at least 2.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 2deda7b1b3dd..c10653be39c0 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -141,6 +141,7 @@ struct io_kiocb {
 	struct io_ring_ctx	*ctx;
 	struct list_head	list;
 	unsigned int		flags;
+	refcount_t		refs;
 #define REQ_F_FORCE_NONBLOCK	1	/* inline submission attempt */
 #define REQ_F_IOPOLL_COMPLETED	2	/* polled IO has completed */
 #define REQ_F_IOPOLL_EAGAIN	4	/* submission got EAGAIN */
@@ -322,6 +323,7 @@ static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx,
 	if (req) {
 		req->ctx = ctx;
 		req->flags = 0;
+		refcount_set(&req->refs, 0);
 		return req;
 	}
 
@@ -341,8 +343,10 @@ static void io_free_req_many(struct io_ring_ctx *ctx, void **reqs, int *nr)
 
 static void io_free_req(struct io_kiocb *req)
 {
-	io_ring_drop_ctx_refs(req->ctx, 1);
-	kmem_cache_free(req_cachep, req);
+	if (!refcount_read(&req->refs) || refcount_dec_and_test(&req->refs)) {
+		io_ring_drop_ctx_refs(req->ctx, 1);
+		kmem_cache_free(req_cachep, req);
+	}
 }
 
 /*
-- 
2.17.1

[PATCH 10/18] io_uring: batch io_kiocb allocation

[Jens Axboe]

Similarly to how we use the state->ios_left to know how many references
to get to a file, we can use it to allocate the io_kiocb's we need in
bulk.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c | 39 ++++++++++++++++++++++++++++++++++++---
 1 file changed, 36 insertions(+), 3 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index e9c237d471ae..497bea0f29c5 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -135,6 +135,13 @@ struct io_kiocb {
 struct io_submit_state {
 	struct blk_plug plug;
 
+	/*
+	 * io_kiocb alloc cache
+	 */
+	void *reqs[IO_IOPOLL_BATCH];
+	unsigned int free_reqs;
+	unsigned int cur_req;
+
 	/*
 	 * File reference cache
 	 */
@@ -258,20 +265,42 @@ static void io_ring_drop_ctx_refs(struct io_ring_ctx *ctx, unsigned refs)
 		wake_up(&ctx->wait);
 }
 
-static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx)
+static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx,
+				   struct io_submit_state *state)
 {
+	gfp_t gfp = GFP_ATOMIC | __GFP_NOWARN;
 	struct io_kiocb *req;
 
 	/* safe to use the non tryget, as we're inside ring ref already */
 	percpu_ref_get(&ctx->refs);
 
-	req = kmem_cache_alloc(req_cachep, GFP_ATOMIC | __GFP_NOWARN);
+	if (!state)
+		req = kmem_cache_alloc(req_cachep, gfp);
+	else if (!state->free_reqs) {
+		size_t sz;
+		int ret;
+
+		sz = min_t(size_t, state->ios_left, ARRAY_SIZE(state->reqs));
+		ret = kmem_cache_alloc_bulk(req_cachep, gfp, sz,
+						state->reqs);
+		if (ret <= 0)
+			goto out;
+		state->free_reqs = ret - 1;
+		state->cur_req = 1;
+		req = state->reqs[0];
+	} else {
+		req = state->reqs[state->cur_req];
+		state->free_reqs--;
+		state->cur_req++;
+	}
+
 	if (req) {
 		req->ctx = ctx;
 		req->flags = 0;
 		return req;
 	}
 
+out:
 	io_ring_drop_ctx_refs(ctx, 1);
 	return NULL;
 }
@@ -883,7 +912,7 @@ static int io_submit_sqe(struct io_ring_ctx *ctx, struct sqe_submit *s,
 	if (unlikely(s->sqe->flags))
 		return -EINVAL;
 
-	req = io_get_req(ctx);
+	req = io_get_req(ctx, state);
 	if (unlikely(!req))
 		return -EAGAIN;
 
@@ -907,6 +936,9 @@ static void io_submit_state_end(struct io_submit_state *state)
 {
 	blk_finish_plug(&state->plug);
 	io_file_put(state, NULL);
+	if (state->free_reqs)
+		kmem_cache_free_bulk(req_cachep, state->free_reqs,
+					&state->reqs[state->cur_req]);
 }
 
 /*
@@ -916,6 +948,7 @@ static void io_submit_state_start(struct io_submit_state *state,
 				  struct io_ring_ctx *ctx, unsigned max_ios)
 {
 	blk_start_plug(&state->plug);
+	state->free_reqs = 0;
 	state->file = NULL;
 	state->ios_left = max_ios;
 }
-- 
2.17.1

[PATCH 11/18] block: implement bio helper to add iter bvec pages to bio

[Jens Axboe]

For an ITER_BVEC, we can just iterate the iov and add the pages
to the bio directly. This requires that the caller doesn't releases
the pages on IO completion, we add a BIO_HOLD_PAGES flag for that.

The current two callers of bio_iov_iter_get_pages() are updated to
check if they need to release pages on completion. This makes them
work with bvecs that contain kernel mapped pages already.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 block/bio.c               | 59 ++++++++++++++++++++++++++++++++-------
 fs/block_dev.c            |  5 ++--
 fs/iomap.c                |  5 ++--
 include/linux/blk_types.h |  1 +
 4 files changed, 56 insertions(+), 14 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 4db1008309ed..7af4f45d2ed6 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -828,6 +828,23 @@ int bio_add_page(struct bio *bio, struct page *page,
 }
 EXPORT_SYMBOL(bio_add_page);
 
+static int __bio_iov_bvec_add_pages(struct bio *bio, struct iov_iter *iter)
+{
+	const struct bio_vec *bv = iter->bvec;
+	unsigned int len;
+	size_t size;
+
+	len = min_t(size_t, bv->bv_len, iter->count);
+	size = bio_add_page(bio, bv->bv_page, len,
+				bv->bv_offset + iter->iov_offset);
+	if (size == len) {
+		iov_iter_advance(iter, size);
+		return 0;
+	}
+
+	return -EINVAL;
+}
+
 #define PAGE_PTRS_PER_BVEC     (sizeof(struct bio_vec) / sizeof(struct page *))
 
 /**
@@ -876,23 +893,43 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 }
 
 /**
- * bio_iov_iter_get_pages - pin user or kernel pages and add them to a bio
+ * bio_iov_iter_get_pages - add user or kernel pages to a bio
  * @bio: bio to add pages to
- * @iter: iov iterator describing the region to be mapped
+ * @iter: iov iterator describing the region to be added
+ *
+ * This takes either an iterator pointing to user memory, or one pointing to
+ * kernel pages (BVEC iterator). If we're adding user pages, we pin them and
+ * map them into the kernel. On IO completion, the caller should put those
+ * pages. If we're adding kernel pages, we just have to add the pages to the
+ * bio directly. We don't grab an extra reference to those pages (the user
+ * should already have that), and we don't put the page on IO completion.
+ * The caller needs to check if the bio is flagged BIO_HOLD_PAGES on IO
+ * completion. If it isn't, then pages should be released.
  *
- * Pins pages from *iter and appends them to @bio's bvec array. The
- * pages will have to be released using put_page() when done.
  * The function tries, but does not guarantee, to pin as many pages as
- * fit into the bio, or are requested in *iter, whatever is smaller.
- * If MM encounters an error pinning the requested pages, it stops.
- * Error is returned only if 0 pages could be pinned.
+ * fit into the bio, or are requested in *iter, whatever is smaller. If
+ * MM encounters an error pinning the requested pages, it stops. Error
+ * is returned only if 0 pages could be pinned.
  */
 int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 {
+	const bool is_bvec = iov_iter_is_bvec(iter);
 	unsigned short orig_vcnt = bio->bi_vcnt;
 
+	/*
+	 * If this is a BVEC iter, then the pages are kernel pages. Don't
+	 * release them on IO completion.
+	 */
+	if (is_bvec)
+		bio_set_flag(bio, BIO_HOLD_PAGES);
+
 	do {
-		int ret = __bio_iov_iter_get_pages(bio, iter);
+		int ret;
+
+		if (is_bvec)
+			ret = __bio_iov_bvec_add_pages(bio, iter);
+		else
+			ret = __bio_iov_iter_get_pages(bio, iter);
 
 		if (unlikely(ret))
 			return bio->bi_vcnt > orig_vcnt ? 0 : ret;
@@ -1634,7 +1671,8 @@ static void bio_dirty_fn(struct work_struct *work)
 		next = bio->bi_private;
 
 		bio_set_pages_dirty(bio);
-		bio_release_pages(bio);
+		if (!bio_flagged(bio, BIO_HOLD_PAGES))
+			bio_release_pages(bio);
 		bio_put(bio);
 	}
 }
@@ -1650,7 +1688,8 @@ void bio_check_pages_dirty(struct bio *bio)
 			goto defer;
 	}
 
-	bio_release_pages(bio);
+	if (!bio_flagged(bio, BIO_HOLD_PAGES))
+		bio_release_pages(bio);
 	bio_put(bio);
 	return;
 defer:
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 392e2bfb636f..fa2720bc0243 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -338,8 +338,9 @@ static void blkdev_bio_end_io(struct bio *bio)
 		struct bio_vec *bvec;
 		int i;
 
-		bio_for_each_segment_all(bvec, bio, i)
-			put_page(bvec->bv_page);
+		if (!bio_flagged(bio, BIO_HOLD_PAGES))
+			bio_for_each_segment_all(bvec, bio, i)
+				put_page(bvec->bv_page);
 		bio_put(bio);
 	}
 }
diff --git a/fs/iomap.c b/fs/iomap.c
index 4ee50b76b4a1..0a64c9c51203 100644
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -1582,8 +1582,9 @@ static void iomap_dio_bio_end_io(struct bio *bio)
 		struct bio_vec *bvec;
 		int i;
 
-		bio_for_each_segment_all(bvec, bio, i)
-			put_page(bvec->bv_page);
+		if (!bio_flagged(bio, BIO_HOLD_PAGES))
+			bio_for_each_segment_all(bvec, bio, i)
+				put_page(bvec->bv_page);
 		bio_put(bio);
 	}
 }
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index 5c7e7f859a24..97e206855cd3 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -215,6 +215,7 @@ struct bio {
 /*
  * bio flags
  */
+#define BIO_HOLD_PAGES	0	/* don't put O_DIRECT pages */
 #define BIO_SEG_VALID	1	/* bi_phys_segments valid */
 #define BIO_CLONED	2	/* doesn't own data */
 #define BIO_BOUNCED	3	/* bio is a bounce bio */
-- 
2.17.1

Re: [PATCH 11/18] block: implement bio helper to add iter bvec pages to bio

[Christoph Hellwig]

> +#define BIO_HOLD_PAGES	0	/* don't put O_DIRECT pages */

They don't really have to be O_DIRECT pages, just something with
a permanent reference.  Maybe rename this to something BIO_NO_PAGE_REF?

Otherwise looks fine:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH 11/18] block: implement bio helper to add iter bvec pages to bio

[Jens Axboe]

On 1/28/19 7:31 AM, Christoph Hellwig wrote:
>> +#define BIO_HOLD_PAGES	0	/* don't put O_DIRECT pages */
> 
> They don't really have to be O_DIRECT pages, just something with
> a permanent reference.  Maybe rename this to something BIO_NO_PAGE_REF?

That is a better name, thanks. I'll make the change.

-- 
Jens Axboe

[PATCH 11/13] io_uring: add support for IORING_OP_POLL

[Jens Axboe]

This is basically a direct port of bfe4037e722e, which implements a
one-shot poll command through aio. Description below is based on that
commit as well. However, instead of adding a POLL command and relying
on io_cancel(2) to remove it, we mimic the epoll(2) interface of
having a command to add a poll notification, IORING_OP_POLL_ADD,
and one to remove it again, IORING_OP_POLL_REMOVE.

To poll for a file descriptor the application should submit an sqe of
type IORING_OP_POLL. It will poll the fd for the events specified in the
poll_events field.

Unlike poll or epoll without EPOLLONESHOT this interface always works in
one shot mode, that is once the sqe is completed, it will have to be
resubmitted.

Based-on-code-from: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c                 | 245 ++++++++++++++++++++++++++++++++++
 include/uapi/linux/io_uring.h |   3 +
 2 files changed, 248 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index c10653be39c0..fe75931d7df5 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -124,6 +124,7 @@ struct io_ring_ctx {
 		spinlock_t		completion_lock;
 		unsigned		poll_multi_file;
 		struct list_head	poll_list;
+		struct list_head	cancel_list;
 	} ____cacheline_aligned_in_smp;
 };
 
@@ -132,9 +133,19 @@ struct sqe_submit {
 	unsigned index;
 };
 
+struct io_poll_iocb {
+	struct file *file;
+	struct wait_queue_head *head;
+	__poll_t events;
+	bool woken;
+	bool canceled;
+	struct wait_queue_entry wait;
+};
+
 struct io_kiocb {
 	union {
 		struct kiocb		rw;
+		struct io_poll_iocb	poll;
 		struct sqe_submit	submit;
 	};
 
@@ -206,6 +217,7 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 	init_waitqueue_head(&ctx->wait);
 	spin_lock_init(&ctx->completion_lock);
 	INIT_LIST_HEAD(&ctx->poll_list);
+	INIT_LIST_HEAD(&ctx->cancel_list);
 	return ctx;
 }
 
@@ -916,6 +928,232 @@ static int io_fsync(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	return 0;
 }
 
+static void io_poll_remove_one(struct io_kiocb *req)
+{
+	struct io_poll_iocb *poll = &req->poll;
+
+	spin_lock(&poll->head->lock);
+	WRITE_ONCE(poll->canceled, true);
+	if (!list_empty(&poll->wait.entry)) {
+		list_del_init(&poll->wait.entry);
+		queue_work(req->ctx->sqo_wq, &req->work);
+	}
+	spin_unlock(&poll->head->lock);
+
+	list_del_init(&req->list);
+}
+
+static void io_poll_remove_all(struct io_ring_ctx *ctx)
+{
+	struct io_kiocb *req;
+
+	spin_lock_irq(&ctx->completion_lock);
+	while (!list_empty(&ctx->cancel_list)) {
+		req = list_first_entry(&ctx->cancel_list, struct io_kiocb,list);
+		io_poll_remove_one(req);
+	}
+	spin_unlock_irq(&ctx->completion_lock);
+}
+
+/*
+ * Find a running poll command that matches one specified in sqe->addr,
+ * and remove it if found.
+ */
+static int io_poll_remove(struct io_kiocb *req, const struct io_uring_sqe *sqe)
+{
+	struct io_ring_ctx *ctx = req->ctx;
+	struct io_kiocb *poll_req, *next;
+	int ret = -ENOENT;
+
+	if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
+		return -EINVAL;
+	if (sqe->ioprio || sqe->off || sqe->len || sqe->buf_index ||
+	    sqe->poll_events)
+		return -EINVAL;
+
+	spin_lock_irq(&ctx->completion_lock);
+	list_for_each_entry_safe(poll_req, next, &ctx->cancel_list, list) {
+		if (sqe->addr == poll_req->user_data) {
+			io_poll_remove_one(poll_req);
+			ret = 0;
+			break;
+		}
+	}
+	spin_unlock_irq(&ctx->completion_lock);
+
+	io_cqring_add_event(req->ctx, sqe->user_data, ret, 0);
+	io_free_req(req);
+	return 0;
+}
+
+static void io_poll_complete(struct io_kiocb *req, __poll_t mask)
+{
+	io_cqring_add_event(req->ctx, req->user_data, mangle_poll(mask), 0);
+	io_fput(req);
+	io_free_req(req);
+}
+
+static void io_poll_complete_work(struct work_struct *work)
+{
+	struct io_kiocb *req = container_of(work, struct io_kiocb, work);
+	struct io_poll_iocb *poll = &req->poll;
+	struct poll_table_struct pt = { ._key = poll->events };
+	struct io_ring_ctx *ctx = req->ctx;
+	__poll_t mask = 0;
+
+	if (!READ_ONCE(poll->canceled))
+		mask = vfs_poll(poll->file, &pt) & poll->events;
+
+	/*
+	 * Note that ->ki_cancel callers also delete iocb from active_reqs after
+	 * calling ->ki_cancel.  We need the ctx_lock roundtrip here to
+	 * synchronize with them.  In the cancellation case the list_del_init
+	 * itself is not actually needed, but harmless so we keep it in to
+	 * avoid further branches in the fast path.
+	 */
+	spin_lock_irq(&ctx->completion_lock);
+	if (!mask && !READ_ONCE(poll->canceled)) {
+		add_wait_queue(poll->head, &poll->wait);
+		spin_unlock_irq(&ctx->completion_lock);
+		return;
+	}
+	list_del_init(&req->list);
+	spin_unlock_irq(&ctx->completion_lock);
+
+	io_poll_complete(req, mask);
+}
+
+static int io_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
+			void *key)
+{
+	struct io_poll_iocb *poll = container_of(wait, struct io_poll_iocb,
+							wait);
+	struct io_kiocb *req = container_of(poll, struct io_kiocb, poll);
+	struct io_ring_ctx *ctx = req->ctx;
+	__poll_t mask = key_to_poll(key);
+
+	poll->woken = true;
+
+	/* for instances that support it check for an event match first: */
+	if (mask) {
+		if (!(mask & poll->events))
+			return 0;
+
+		/* try to complete the iocb inline if we can: */
+		if (spin_trylock(&ctx->completion_lock)) {
+			list_del(&req->list);
+			spin_unlock(&ctx->completion_lock);
+
+			list_del_init(&poll->wait.entry);
+			io_poll_complete(req, mask);
+			return 1;
+		}
+	}
+
+	list_del_init(&poll->wait.entry);
+	queue_work(ctx->sqo_wq, &req->work);
+	return 1;
+}
+
+struct io_poll_table {
+	struct poll_table_struct pt;
+	struct io_kiocb *req;
+	int error;
+};
+
+static void io_poll_queue_proc(struct file *file, struct wait_queue_head *head,
+			       struct poll_table_struct *p)
+{
+	struct io_poll_table *pt = container_of(p, struct io_poll_table, pt);
+
+	if (unlikely(pt->req->poll.head)) {
+		pt->error = -EINVAL;
+		return;
+	}
+
+	pt->error = 0;
+	pt->req->poll.head = head;
+	add_wait_queue(head, &pt->req->poll.wait);
+}
+
+static int io_poll_add(struct io_kiocb *req, const struct io_uring_sqe *sqe)
+{
+	struct io_poll_iocb *poll = &req->poll;
+	struct io_ring_ctx *ctx = req->ctx;
+	struct io_poll_table ipt;
+	__poll_t mask;
+
+	if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
+		return -EINVAL;
+	if (sqe->addr || sqe->ioprio || sqe->off || sqe->len || sqe->buf_index)
+		return -EINVAL;
+
+	INIT_WORK(&req->work, io_poll_complete_work);
+	poll->events = demangle_poll(sqe->poll_events) | EPOLLERR | EPOLLHUP;
+
+	if (sqe->flags & IOSQE_FIXED_FILE) {
+		if (unlikely(!ctx->user_files || sqe->fd >= ctx->nr_user_files))
+			return -EBADF;
+		poll->file = ctx->user_files[sqe->fd];
+		req->flags |= REQ_F_FIXED_FILE;
+	} else {
+		poll->file = fget(sqe->fd);
+	}
+	if (unlikely(!poll->file))
+		return -EBADF;
+
+	poll->head = NULL;
+	poll->woken = false;
+	poll->canceled = false;
+
+	ipt.pt._qproc = io_poll_queue_proc;
+	ipt.pt._key = poll->events;
+	ipt.req = req;
+	ipt.error = -EINVAL; /* same as no support for IOCB_CMD_POLL */
+
+	/* initialized the list so that we can do list_empty checks */
+	INIT_LIST_HEAD(&poll->wait.entry);
+	init_waitqueue_func_entry(&poll->wait, io_poll_wake);
+
+	/* one for removal from waitqueue, one for this function */
+	refcount_set(&req->refs, 2);
+
+	mask = vfs_poll(poll->file, &ipt.pt) & poll->events;
+	if (unlikely(!poll->head)) {
+		/* we did not manage to set up a waitqueue, done */
+		goto out;
+	}
+
+	spin_lock_irq(&ctx->completion_lock);
+	spin_lock(&poll->head->lock);
+	if (poll->woken) {
+		/* wake_up context handles the rest */
+		mask = 0;
+		ipt.error = 0;
+	} else if (mask || ipt.error) {
+		/* if we get an error or a mask we are done */
+		WARN_ON_ONCE(list_empty(&poll->wait.entry));
+		list_del_init(&poll->wait.entry);
+	} else {
+		/* actually waiting for an event */
+		list_add_tail(&req->list, &ctx->cancel_list);
+	}
+	spin_unlock(&poll->head->lock);
+	spin_unlock_irq(&ctx->completion_lock);
+
+out:
+	if (unlikely(ipt.error)) {
+		if (!(sqe->flags & IOSQE_FIXED_FILE))
+			fput(poll->file);
+		return ipt.error;
+	}
+
+	if (mask)
+		io_poll_complete(req, mask);
+	io_free_req(req);
+	return 0;
+}
+
 static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 			   struct sqe_submit *s, bool force_nonblock,
 			   struct io_submit_state *state)
@@ -951,6 +1189,12 @@ static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 	case IORING_OP_FSYNC:
 		ret = io_fsync(req, sqe, force_nonblock);
 		break;
+	case IORING_OP_POLL_ADD:
+		ret = io_poll_add(req, sqe);
+		break;
+	case IORING_OP_POLL_REMOVE:
+		ret = io_poll_remove(req, sqe);
+		break;
 	default:
 		ret = -EINVAL;
 		break;
@@ -1794,6 +2038,7 @@ static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
 	percpu_ref_kill(&ctx->refs);
 	mutex_unlock(&ctx->uring_lock);
 
+	io_poll_remove_all(ctx);
 	io_iopoll_reap_events(ctx);
 	wait_for_completion(&ctx->ctx_done);
 	io_ring_ctx_free(ctx);
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 37c7402be9ca..60b52c551c87 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -27,6 +27,7 @@ struct io_uring_sqe {
 	union {
 		__kernel_rwf_t	rw_flags;
 		__u32		fsync_flags;
+		__u16		poll_events;
 	};
 	__u64	user_data;	/* data to be passed back at completion time */
 	union {
@@ -53,6 +54,8 @@ struct io_uring_sqe {
 #define IORING_OP_FSYNC		3
 #define IORING_OP_READ_FIXED	4
 #define IORING_OP_WRITE_FIXED	5
+#define IORING_OP_POLL_ADD	6
+#define IORING_OP_POLL_REMOVE	7
 
 /*
  * sqe->fsync_flags
-- 
2.17.1

[PATCH 12/18] io_uring: add support for pre-mapped user IO buffers

[Jens Axboe]

If we have fixed user buffers, we can map them into the kernel when we
setup the io_context. That avoids the need to do get_user_pages() for
each and every IO.

To utilize this feature, the application must call io_uring_register()
after having setup an io_uring context, passing in
IORING_REGISTER_BUFFERS as the opcode. The argument must be a pointer
to an iovec array, and the nr_args should contain how many iovecs the
application wishes to map.

If successful, these buffers are now mapped into the kernel, eligible
for IO. To use these fixed buffers, the application must use the
IORING_OP_READ_FIXED and IORING_OP_WRITE_FIXED opcodes, and then
set sqe->index to the desired buffer index. sqe->addr..sqe->addr+seq->len
must point to somewhere inside the indexed buffer.

The application may register buffers throughout the lifetime of the
io_uring context. It can call io_uring_register() with
IORING_UNREGISTER_BUFFERS as the opcode to unregister the current set of
buffers, and then register a new set. The application need not
unregister buffers explicitly before shutting down the io_uring context.

It's perfectly valid to setup a larger buffer, and then sometimes only
use parts of it for an IO. As long as the range is within the originally
mapped region, it will work just fine.

For now, buffers must not be file backed. If file backed buffers are
passed in, the registration will fail with -1/EOPNOTSUPP. This
restriction may be relaxed in the future.

RLIMIT_MEMLOCK is used to check how much memory we can pin. A somewhat
arbitrary 1G per buffer size is also imposed.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 arch/x86/entry/syscalls/syscall_32.tbl |   1 +
 arch/x86/entry/syscalls/syscall_64.tbl |   1 +
 fs/io_uring.c                          | 357 ++++++++++++++++++++++++-
 include/linux/sched/user.h             |   2 +-
 include/linux/syscalls.h               |   2 +
 include/uapi/asm-generic/unistd.h      |   4 +-
 include/uapi/linux/io_uring.h          |  13 +-
 kernel/sys_ni.c                        |   1 +
 8 files changed, 367 insertions(+), 14 deletions(-)

diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index a6076d1e2154..7cdbd0712df5 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -400,3 +400,4 @@
 386	i386	rseq			sys_rseq			__ia32_sys_rseq
 425	i386	io_uring_setup		sys_io_uring_setup		__ia32_compat_sys_io_uring_setup
 426	i386	io_uring_enter		sys_io_uring_enter		__ia32_sys_io_uring_enter
+427	i386	io_uring_register	sys_io_uring_register		__ia32_sys_io_uring_register
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index 6a32a430c8e0..65c026185e61 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -345,6 +345,7 @@
 334	common	rseq			__x64_sys_rseq
 425	common	io_uring_setup		__x64_sys_io_uring_setup
 426	common	io_uring_enter		__x64_sys_io_uring_enter
+427	common	io_uring_register	__x64_sys_io_uring_register
 
 #
 # x32-specific system call numbers start at 512 to avoid cache impact
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 497bea0f29c5..63ad09e7cdc7 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -25,8 +25,11 @@
 #include <linux/slab.h>
 #include <linux/workqueue.h>
 #include <linux/blkdev.h>
+#include <linux/bvec.h>
 #include <linux/anon_inodes.h>
 #include <linux/sched/mm.h>
+#include <linux/sizes.h>
+#include <linux/nospec.h>
 
 #include <linux/uaccess.h>
 #include <linux/nospec.h>
@@ -57,6 +60,13 @@ struct io_cq_ring {
 	struct io_uring_cqe	cqes[];
 };
 
+struct io_mapped_ubuf {
+	u64		ubuf;
+	size_t		len;
+	struct		bio_vec *bvec;
+	unsigned int	nr_bvecs;
+};
+
 struct io_ring_ctx {
 	struct {
 		struct percpu_ref	refs;
@@ -90,6 +100,10 @@ struct io_ring_ctx {
 		struct fasync_struct	*cq_fasync;
 	} ____cacheline_aligned_in_smp;
 
+	/* if used, fixed mapped user buffers */
+	unsigned		nr_user_bufs;
+	struct io_mapped_ubuf	*user_bufs;
+
 	struct user_struct	*user;
 
 	struct completion	ctx_done;
@@ -664,12 +678,51 @@ static inline void io_rw_done(struct kiocb *kiocb, ssize_t ret)
 	}
 }
 
+static int io_import_fixed(struct io_ring_ctx *ctx, int rw,
+			   const struct io_uring_sqe *sqe,
+			   struct iov_iter *iter)
+{
+	struct io_mapped_ubuf *imu;
+	size_t len = sqe->len;
+	size_t offset;
+	int index;
+
+	/* attempt to use fixed buffers without having provided iovecs */
+	if (unlikely(!ctx->user_bufs))
+		return -EFAULT;
+	if (unlikely(sqe->buf_index >= ctx->nr_user_bufs))
+		return -EFAULT;
+
+	index = array_index_nospec(sqe->buf_index, ctx->sq_entries);
+	imu = &ctx->user_bufs[index];
+	if ((unsigned long) sqe->addr < imu->ubuf ||
+	    (unsigned long) sqe->addr + len > imu->ubuf + imu->len)
+		return -EFAULT;
+
+	/*
+	 * May not be a start of buffer, set size appropriately
+	 * and advance us to the beginning.
+	 */
+	offset = (unsigned long) sqe->addr - imu->ubuf;
+	iov_iter_bvec(iter, rw, imu->bvec, imu->nr_bvecs, offset + len);
+	if (offset)
+		iov_iter_advance(iter, offset);
+	return 0;
+}
+
 static int io_import_iovec(struct io_ring_ctx *ctx, int rw,
 			   const struct io_uring_sqe *sqe,
 			   struct iovec **iovec, struct iov_iter *iter)
 {
 	void __user *buf = u64_to_user_ptr(sqe->addr);
 
+	if (sqe->opcode == IORING_OP_READ_FIXED ||
+	    sqe->opcode == IORING_OP_WRITE_FIXED) {
+		ssize_t ret = io_import_fixed(ctx, rw, sqe, iter);
+		*iovec = NULL;
+		return ret;
+	}
+
 #ifdef CONFIG_COMPAT
 	if (ctx->compat)
 		return compat_import_iovec(rw, buf, sqe->len, UIO_FASTIOV,
@@ -805,7 +858,7 @@ static int io_fsync(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 
 	if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
 		return -EINVAL;
-	if (unlikely(sqe->addr || sqe->ioprio))
+	if (unlikely(sqe->addr || sqe->ioprio || sqe->buf_index))
 		return -EINVAL;
 	if (unlikely(sqe->fsync_flags & ~IORING_FSYNC_DATASYNC))
 		return -EINVAL;
@@ -840,9 +893,19 @@ static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 		ret = io_nop(req, sqe);
 		break;
 	case IORING_OP_READV:
+		if (unlikely(sqe->buf_index))
+			return -EINVAL;
 		ret = io_read(req, sqe, force_nonblock, state);
 		break;
 	case IORING_OP_WRITEV:
+		if (unlikely(sqe->buf_index))
+			return -EINVAL;
+		ret = io_write(req, sqe, force_nonblock, state);
+		break;
+	case IORING_OP_READ_FIXED:
+		ret = io_read(req, sqe, force_nonblock, state);
+		break;
+	case IORING_OP_WRITE_FIXED:
 		ret = io_write(req, sqe, force_nonblock, state);
 		break;
 	case IORING_OP_FSYNC:
@@ -865,14 +928,21 @@ static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 	return 0;
 }
 
+static inline bool io_sqe_needs_user(const struct io_uring_sqe *sqe)
+{
+	return !(sqe->opcode == IORING_OP_READ_FIXED ||
+		 sqe->opcode == IORING_OP_WRITE_FIXED);
+}
+
 static void io_sq_wq_submit_work(struct work_struct *work)
 {
 	struct io_kiocb *req = container_of(work, struct io_kiocb, work);
 	struct sqe_submit *s = &req->submit;
 	u64 user_data = s->sqe->user_data;
 	struct io_ring_ctx *ctx = req->ctx;
-	mm_segment_t old_fs = get_fs();
 	struct files_struct *old_files;
+	mm_segment_t old_fs;
+	bool needs_user;
 	int ret;
 
 	 /* Ensure we clear previously set forced non-block flag */
@@ -881,19 +951,28 @@ static void io_sq_wq_submit_work(struct work_struct *work)
 	old_files = current->files;
 	current->files = ctx->sqo_files;
 
-	if (!mmget_not_zero(ctx->sqo_mm)) {
-		ret = -EFAULT;
-		goto err;
+	/*
+	 * If we're doing IO to fixed buffers, we don't need to get/set
+	 * user context
+	 */
+	needs_user = io_sqe_needs_user(s->sqe);
+	if (needs_user) {
+		if (!mmget_not_zero(ctx->sqo_mm)) {
+			ret = -EFAULT;
+			goto err;
+		}
+		use_mm(ctx->sqo_mm);
+		old_fs = get_fs();
+		set_fs(USER_DS);
 	}
 
-	use_mm(ctx->sqo_mm);
-	set_fs(USER_DS);
-
 	ret = __io_submit_sqe(ctx, req, s, false, NULL);
 
-	set_fs(old_fs);
-	unuse_mm(ctx->sqo_mm);
-	mmput(ctx->sqo_mm);
+	if (needs_user) {
+		set_fs(old_fs);
+		unuse_mm(ctx->sqo_mm);
+		mmput(ctx->sqo_mm);
+	}
 err:
 	if (ret) {
 		io_cqring_add_event(ctx, user_data, ret, 0);
@@ -1163,6 +1242,14 @@ static int __io_account_mem(struct user_struct *user, unsigned long nr_pages)
 	return 0;
 }
 
+static int io_account_mem(struct io_ring_ctx *ctx, unsigned long nr_pages)
+{
+	if (ctx->user)
+		return __io_account_mem(ctx->user, nr_pages);
+
+	return 0;
+}
+
 static unsigned long ring_pages(unsigned sq_entries, unsigned cq_entries)
 {
 	struct io_sq_ring *sq_ring;
@@ -1176,6 +1263,190 @@ static unsigned long ring_pages(unsigned sq_entries, unsigned cq_entries)
 	return (bytes + PAGE_SIZE - 1) / PAGE_SIZE;
 }
 
+static int io_sqe_buffer_unregister(struct io_ring_ctx *ctx)
+{
+	int i, j;
+
+	if (!ctx->user_bufs)
+		return -ENXIO;
+
+	for (i = 0; i < ctx->sq_entries; i++) {
+		struct io_mapped_ubuf *imu = &ctx->user_bufs[i];
+
+		for (j = 0; j < imu->nr_bvecs; j++)
+			put_page(imu->bvec[j].bv_page);
+
+		io_unaccount_mem(ctx, imu->nr_bvecs);
+		kfree(imu->bvec);
+		imu->nr_bvecs = 0;
+	}
+
+	kfree(ctx->user_bufs);
+	ctx->user_bufs = NULL;
+	free_uid(ctx->user);
+	ctx->user = NULL;
+	return 0;
+}
+
+static int io_copy_iov(struct io_ring_ctx *ctx, struct iovec *dst,
+		       void __user *arg, unsigned index)
+{
+	struct iovec __user *src;
+
+#ifdef CONFIG_COMPAT
+	if (ctx->compat) {
+		struct compat_iovec __user *ciovs;
+		struct compat_iovec ciov;
+
+		ciovs = (struct compat_iovec __user *) arg;
+		if (copy_from_user(&ciov, &ciovs[index], sizeof(ciov)))
+			return -EFAULT;
+
+		dst->iov_base = (void __user *) (unsigned long) ciov.iov_base;
+		dst->iov_len = ciov.iov_len;
+		return 0;
+	}
+#endif
+	src = (struct iovec __user *) arg;
+	if (copy_from_user(dst, &src[index], sizeof(*dst)))
+		return -EFAULT;
+	return 0;
+}
+
+static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg,
+				  unsigned nr_args)
+{
+	struct vm_area_struct **vmas = NULL;
+	struct page **pages = NULL;
+	int i, j, got_pages = 0;
+	int ret = -EINVAL;
+
+	if (ctx->user_bufs)
+		return -EBUSY;
+	if (!nr_args || nr_args > UIO_MAXIOV)
+		return -EINVAL;
+
+	ctx->user_bufs = kcalloc(nr_args, sizeof(struct io_mapped_ubuf),
+					GFP_KERNEL);
+	if (!ctx->user_bufs)
+		return -ENOMEM;
+
+	if (!capable(CAP_IPC_LOCK))
+		ctx->user = get_uid(current_user());
+
+	for (i = 0; i < nr_args; i++) {
+		struct io_mapped_ubuf *imu = &ctx->user_bufs[i];
+		unsigned long off, start, end, ubuf;
+		int pret, nr_pages;
+		struct iovec iov;
+		size_t size;
+
+		ret = io_copy_iov(ctx, &iov, arg, i);
+		if (ret)
+			break;
+
+		/*
+		 * Don't impose further limits on the size and buffer
+		 * constraints here, we'll -EINVAL later when IO is
+		 * submitted if they are wrong.
+		 */
+		ret = -EFAULT;
+		if (!iov.iov_base)
+			goto err;
+
+		/* arbitrary limit, but we need something */
+		if (iov.iov_len > SZ_1G)
+			goto err;
+
+		ubuf = (unsigned long) iov.iov_base;
+		end = (ubuf + iov.iov_len + PAGE_SIZE - 1) >> PAGE_SHIFT;
+		start = ubuf >> PAGE_SHIFT;
+		nr_pages = end - start;
+
+		ret = io_account_mem(ctx, nr_pages);
+		if (ret)
+			goto err;
+
+		if (!pages || nr_pages > got_pages) {
+			kfree(vmas);
+			kfree(pages);
+			pages = kmalloc_array(nr_pages, sizeof(struct page *),
+						GFP_KERNEL);
+			vmas = kmalloc_array(nr_pages,
+					sizeof(struct vma_area_struct *),
+					GFP_KERNEL);
+			if (!pages || !vmas) {
+				io_unaccount_mem(ctx, nr_pages);
+				goto err;
+			}
+			got_pages = nr_pages;
+		}
+
+		imu->bvec = kmalloc_array(nr_pages, sizeof(struct bio_vec),
+						GFP_KERNEL);
+		if (!imu->bvec) {
+			io_unaccount_mem(ctx, nr_pages);
+			goto err;
+		}
+
+		down_write(&current->mm->mmap_sem);
+		pret = get_user_pages_longterm(ubuf, nr_pages, FOLL_WRITE,
+						pages, vmas);
+		if (pret == nr_pages) {
+			/* don't support file backed memory */
+			for (j = 0; j < nr_pages; j++) {
+				struct vm_area_struct *vma = vmas[j];
+
+				if (vma->vm_file) {
+					ret = -EOPNOTSUPP;
+					break;
+				}
+			}
+		} else {
+			ret = pret < 0 ? pret : -EFAULT;
+		}
+		up_write(&current->mm->mmap_sem);
+		if (ret) {
+			/*
+			 * if we did partial map, or found file backed vmas,
+			 * release any pages we did get
+			 */
+			if (pret > 0) {
+				for (j = 0; j < pret; j++)
+					put_page(pages[j]);
+			}
+			io_unaccount_mem(ctx, nr_pages);
+			goto err;
+		}
+
+		off = ubuf & ~PAGE_MASK;
+		size = iov.iov_len;
+		for (j = 0; j < nr_pages; j++) {
+			size_t vec_len;
+
+			vec_len = min_t(size_t, size, PAGE_SIZE - off);
+			imu->bvec[j].bv_page = pages[j];
+			imu->bvec[j].bv_len = vec_len;
+			imu->bvec[j].bv_offset = off;
+			off = 0;
+			size -= vec_len;
+		}
+		/* store original address for later verification */
+		imu->ubuf = ubuf;
+		imu->len = iov.iov_len;
+		imu->nr_bvecs = nr_pages;
+	}
+	kfree(pages);
+	kfree(vmas);
+	ctx->nr_user_bufs = nr_args;
+	return 0;
+err:
+	kfree(pages);
+	kfree(vmas);
+	io_sqe_buffer_unregister(ctx);
+	return ret;
+}
+
 static void io_free_scq_urings(struct io_ring_ctx *ctx)
 {
 	if (ctx->sq_ring) {
@@ -1197,6 +1468,7 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx)
 	io_sq_offload_stop(ctx);
 	io_iopoll_reap_events(ctx);
 	io_free_scq_urings(ctx);
+	io_sqe_buffer_unregister(ctx);
 	percpu_ref_exit(&ctx->refs);
 	io_unaccount_mem(ctx, ring_pages(ctx->sq_entries, ctx->cq_entries));
 	kfree(ctx);
@@ -1488,6 +1760,69 @@ COMPAT_SYSCALL_DEFINE2(io_uring_setup, u32, entries,
 }
 #endif
 
+static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
+			       void __user *arg, unsigned nr_args)
+{
+	int ret;
+
+	/* Drop our initial ref and wait for the ctx to be fully idle */
+	percpu_ref_put(&ctx->refs);
+	percpu_ref_kill(&ctx->refs);
+	wait_for_completion(&ctx->ctx_done);
+
+	switch (opcode) {
+	case IORING_REGISTER_BUFFERS:
+		ret = io_sqe_buffer_register(ctx, arg, nr_args);
+		break;
+	case IORING_UNREGISTER_BUFFERS:
+		ret = -EINVAL;
+		if (arg || nr_args)
+			break;
+		ret = io_sqe_buffer_unregister(ctx);
+		break;
+	default:
+		ret = -EINVAL;
+		break;
+	}
+
+	/* bring the ctx back to life */
+	reinit_completion(&ctx->ctx_done);
+	percpu_ref_resurrect(&ctx->refs);
+	percpu_ref_get(&ctx->refs);
+	return ret;
+}
+
+SYSCALL_DEFINE4(io_uring_register, unsigned int, fd, unsigned int, opcode,
+		void __user *, arg, unsigned int, nr_args)
+{
+	struct io_ring_ctx *ctx;
+	long ret = -EBADF;
+	struct fd f;
+
+	f = fdget(fd);
+	if (!f.file)
+		return -EBADF;
+
+	ret = -EOPNOTSUPP;
+	if (f.file->f_op != &io_uring_fops)
+		goto out_fput;
+
+	ret = -ENXIO;
+	ctx = f.file->private_data;
+	if (!percpu_ref_tryget(&ctx->refs))
+		goto out_fput;
+
+	ret = -EBUSY;
+	if (mutex_trylock(&ctx->uring_lock)) {
+		ret = __io_uring_register(ctx, opcode, arg, nr_args);
+		mutex_unlock(&ctx->uring_lock);
+	}
+	io_ring_drop_ctx_refs(ctx, 1);
+out_fput:
+	fdput(f);
+	return ret;
+}
+
 static int __init io_uring_init(void)
 {
 	req_cachep = KMEM_CACHE(io_kiocb, SLAB_HWCACHE_ALIGN | SLAB_PANIC);
diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h
index 39ad98c09c58..c7b5f86b91a1 100644
--- a/include/linux/sched/user.h
+++ b/include/linux/sched/user.h
@@ -40,7 +40,7 @@ struct user_struct {
 	kuid_t uid;
 
 #if defined(CONFIG_PERF_EVENTS) || defined(CONFIG_BPF_SYSCALL) || \
-    defined(CONFIG_NET)
+    defined(CONFIG_NET) || defined(CONFIG_IO_URING)
 	atomic_long_t locked_vm;
 #endif
 
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 542757a4c898..101f7024d154 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -314,6 +314,8 @@ asmlinkage long sys_io_uring_setup(u32 entries,
 				struct io_uring_params __user *p);
 asmlinkage long sys_io_uring_enter(unsigned int fd, u32 to_submit,
 				u32 min_complete, u32 flags);
+asmlinkage long sys_io_uring_register(unsigned int fd, unsigned int op,
+				void __user *arg, unsigned int nr_args);
 
 /* fs/xattr.c */
 asmlinkage long sys_setxattr(const char __user *path, const char __user *name,
diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index 87871e7b7ea7..d346229a1eb0 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -744,9 +744,11 @@ __SYSCALL(__NR_kexec_file_load,     sys_kexec_file_load)
 __SYSCALL(__NR_io_uring_setup, sys_io_uring_setup)
 #define __NR_io_uring_enter 426
 __SYSCALL(__NR_io_uring_enter, sys_io_uring_enter)
+#define __NR_io_uring_register 427
+__SYSCALL(__NR_io_uring_register, sys_io_uring_register)
 
 #undef __NR_syscalls
-#define __NR_syscalls 427
+#define __NR_syscalls 428
 
 /*
  * 32 bit systems traditionally used different
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 4fc5fbd07688..03ce7133c3b2 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -29,7 +29,10 @@ struct io_uring_sqe {
 		__u32		fsync_flags;
 	};
 	__u64	user_data;	/* data to be passed back at completion time */
-	__u64	__pad2[3];
+	union {
+		__u16	buf_index;	/* index into fixed buffers, if used */
+		__u64	__pad2[3];
+	};
 };
 
 /*
@@ -41,6 +44,8 @@ struct io_uring_sqe {
 #define IORING_OP_READV		1
 #define IORING_OP_WRITEV	2
 #define IORING_OP_FSYNC		3
+#define IORING_OP_READ_FIXED	4
+#define IORING_OP_WRITE_FIXED	5
 
 /*
  * sqe->fsync_flags
@@ -104,4 +109,10 @@ struct io_uring_params {
 	struct io_cqring_offsets cq_off;
 };
 
+/*
+ * io_uring_register(2) opcodes and arguments
+ */
+#define IORING_REGISTER_BUFFERS		0
+#define IORING_UNREGISTER_BUFFERS	1
+
 #endif
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index d754811ec780..38567718c397 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -49,6 +49,7 @@ COND_SYSCALL_COMPAT(io_pgetevents);
 COND_SYSCALL(io_uring_setup);
 COND_SYSCALL_COMPAT(io_uring_setup);
 COND_SYSCALL(io_uring_enter);
+COND_SYSCALL(io_uring_register);
 
 /* fs/xattr.c */
 
-- 
2.17.1

[PATCH 12/13] io_uring: allow workqueue item to handle multiple buffered requests

[Jens Axboe]

Right now we punt any buffered request that ends up triggering an
-EAGAIN to an async workqueue. This works fine in terms of providing
async execution of them, but it also can create quite a lot of work
queue items. For sequentially buffered IO, it's advantageous to
serialize the issue of them. For reads, the first one will trigger a
read-ahead, and subsequent request merely end up waiting on later pages
to complete. For writes, devices usually respond better to streamed
sequential writes.

Add state to track the last buffered request we punted to a work queue,
and if the next one is sequential to the previous, attempt to get the
previous work item to handle it. We limit the number of sequential
add-ons to the a multiple (8) of the max read-ahead size of the file.
This should be a good number for both reads and wries, as it defines the
max IO size the device can do directly.

This drastically cuts down on the number of context switches we need to
handle buffered sequential IO, and a basic test case of copying a big
file with io_uring sees a 5x speedup.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c | 231 ++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 194 insertions(+), 37 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index fe75931d7df5..aa903fa902d5 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -68,6 +68,16 @@ struct io_mapped_ubuf {
 	unsigned int	nr_bvecs;
 };
 
+struct async_list {
+	spinlock_t		lock;
+	atomic_t		cnt;
+	struct list_head	list;
+
+	struct file		*file;
+	off_t			io_end;
+	size_t			io_pages;
+};
+
 struct io_ring_ctx {
 	struct {
 		struct percpu_ref	refs;
@@ -126,6 +136,8 @@ struct io_ring_ctx {
 		struct list_head	poll_list;
 		struct list_head	cancel_list;
 	} ____cacheline_aligned_in_smp;
+
+	struct async_list	pending_async[2];
 };
 
 struct sqe_submit {
@@ -157,6 +169,7 @@ struct io_kiocb {
 #define REQ_F_IOPOLL_COMPLETED	2	/* polled IO has completed */
 #define REQ_F_IOPOLL_EAGAIN	4	/* submission got EAGAIN */
 #define REQ_F_FIXED_FILE	8	/* ctx owns file */
+#define REQ_F_SEQ_PREV		16	/* sequential with previous */
 	u64			user_data;
 	u64			res;
 
@@ -200,6 +213,7 @@ static void io_ring_ctx_ref_free(struct percpu_ref *ref)
 static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 {
 	struct io_ring_ctx *ctx;
+	int i;
 
 	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
 	if (!ctx)
@@ -215,6 +229,11 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 	init_completion(&ctx->ctx_done);
 	mutex_init(&ctx->uring_lock);
 	init_waitqueue_head(&ctx->wait);
+	for (i = 0; i < ARRAY_SIZE(ctx->pending_async); i++) {
+		spin_lock_init(&ctx->pending_async[i].lock);
+		INIT_LIST_HEAD(&ctx->pending_async[i].list);
+		atomic_set(&ctx->pending_async[i].cnt, 0);
+	}
 	spin_lock_init(&ctx->completion_lock);
 	INIT_LIST_HEAD(&ctx->poll_list);
 	INIT_LIST_HEAD(&ctx->cancel_list);
@@ -774,6 +793,39 @@ static int io_import_iovec(struct io_ring_ctx *ctx, int rw,
 	return import_iovec(rw, buf, sqe->len, UIO_FASTIOV, iovec, iter);
 }
 
+static void io_async_list_note(int rw, struct io_kiocb *req, size_t len)
+{
+	struct async_list *async_list = &req->ctx->pending_async[rw];
+	struct kiocb *kiocb = &req->rw;
+	struct file *filp = kiocb->ki_filp;
+	off_t io_end = kiocb->ki_pos + len;
+
+	if (filp == async_list->file && kiocb->ki_pos == async_list->io_end) {
+		unsigned long max_pages;
+
+		/* Use 8x RA size as a decent limiter for both reads/writes */
+		max_pages = filp->f_ra.ra_pages;
+		if (!max_pages)
+			max_pages = VM_MAX_READAHEAD >> (PAGE_SHIFT - 10);
+		max_pages *= 8;
+
+		len >>= PAGE_SHIFT;
+		if (async_list->io_pages + len <= max_pages) {
+			req->flags |= REQ_F_SEQ_PREV;
+			async_list->io_pages += len;
+		} else {
+			io_end = 0;
+			async_list->io_pages = 0;
+		}
+	}
+
+	if (async_list->file != filp) {
+		async_list->io_pages = 0;
+		async_list->file = filp;
+	}
+	async_list->io_end = io_end;
+}
+
 static ssize_t io_read(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 		       bool force_nonblock, struct io_submit_state *state)
 {
@@ -781,6 +833,7 @@ static ssize_t io_read(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	struct kiocb *kiocb = &req->rw;
 	struct iov_iter iter;
 	struct file *file;
+	size_t iov_count;
 	ssize_t ret;
 
 	ret = io_prep_rw(req, sqe, force_nonblock, state);
@@ -799,16 +852,19 @@ static ssize_t io_read(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	if (ret)
 		goto out_fput;
 
-	ret = rw_verify_area(READ, file, &kiocb->ki_pos, iov_iter_count(&iter));
+	iov_count = iov_iter_count(&iter);
+	ret = rw_verify_area(READ, file, &kiocb->ki_pos, iov_count);
 	if (!ret) {
 		ssize_t ret2;
 
 		/* Catch -EAGAIN return for forced non-blocking submission */
 		ret2 = call_read_iter(file, kiocb, &iter);
-		if (!force_nonblock || ret2 != -EAGAIN)
+		if (!force_nonblock || ret2 != -EAGAIN) {
 			io_rw_done(kiocb, ret2);
-		else
+		} else {
+			io_async_list_note(READ, req, iov_count);
 			ret = -EAGAIN;
+		}
 	}
 	kfree(iovec);
 out_fput:
@@ -824,6 +880,7 @@ static ssize_t io_write(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	struct kiocb *kiocb = &req->rw;
 	struct iov_iter iter;
 	struct file *file;
+	size_t iov_count;
 	ssize_t ret;
 
 	ret = io_prep_rw(req, sqe, force_nonblock, state);
@@ -831,10 +888,6 @@ static ssize_t io_write(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 		return ret;
 	file = kiocb->ki_filp;
 
-	ret = -EAGAIN;
-	if (force_nonblock && !(kiocb->ki_flags & IOCB_DIRECT))
-		goto out_fput;
-
 	ret = -EBADF;
 	if (unlikely(!(file->f_mode & FMODE_WRITE)))
 		goto out_fput;
@@ -846,8 +899,15 @@ static ssize_t io_write(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	if (ret)
 		goto out_fput;
 
-	ret = rw_verify_area(WRITE, file, &kiocb->ki_pos,
-				iov_iter_count(&iter));
+	iov_count = iov_iter_count(&iter);
+
+	ret = -EAGAIN;
+	if (force_nonblock && !(kiocb->ki_flags & IOCB_DIRECT)) {
+		io_async_list_note(WRITE, req, iov_count);
+		goto out_free;
+	}
+
+	ret = rw_verify_area(WRITE, file, &kiocb->ki_pos, iov_count);
 	if (!ret) {
 		/*
 		 * Open-code file_start_write here to grab freeze protection,
@@ -865,6 +925,7 @@ static ssize_t io_write(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 		kiocb->ki_flags |= IOCB_WRITE;
 		io_rw_done(kiocb, call_write_iter(file, kiocb, &iter));
 	}
+out_free:
 	kfree(iovec);
 out_fput:
 	if (unlikely(ret))
@@ -1212,6 +1273,21 @@ static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 	return 0;
 }
 
+static struct async_list *io_async_list_from_sqe(struct io_ring_ctx *ctx,
+						 const struct io_uring_sqe *sqe)
+{
+	switch (sqe->opcode) {
+	case IORING_OP_READV:
+	case IORING_OP_READ_FIXED:
+		return &ctx->pending_async[READ];
+	case IORING_OP_WRITEV:
+	case IORING_OP_WRITE_FIXED:
+		return &ctx->pending_async[WRITE];
+	default:
+		return NULL;
+	}
+}
+
 static inline bool io_sqe_needs_user(const struct io_uring_sqe *sqe)
 {
 	return !(sqe->opcode == IORING_OP_READ_FIXED ||
@@ -1221,50 +1297,124 @@ static inline bool io_sqe_needs_user(const struct io_uring_sqe *sqe)
 static void io_sq_wq_submit_work(struct work_struct *work)
 {
 	struct io_kiocb *req = container_of(work, struct io_kiocb, work);
-	struct sqe_submit *s = &req->submit;
-	u64 user_data = s->sqe->user_data;
 	struct io_ring_ctx *ctx = req->ctx;
+	struct mm_struct *cur_mm = NULL;
 	struct files_struct *old_files;
+	struct async_list *async_list;
+	LIST_HEAD(req_list);
 	mm_segment_t old_fs;
-	bool needs_user;
 	int ret;
 
-	 /* Ensure we clear previously set forced non-block flag */
-	req->flags &= ~REQ_F_FORCE_NONBLOCK;
-
 	old_files = current->files;
 	current->files = ctx->sqo_files;
 
+	async_list = io_async_list_from_sqe(ctx, req->submit.sqe);
+restart:
+	do {
+		struct sqe_submit *s = &req->submit;
+		u64 user_data = s->sqe->user_data;
+
+		/* Ensure we clear previously set forced non-block flag */
+		req->flags &= ~REQ_F_FORCE_NONBLOCK;
+
+		ret = 0;
+		if (io_sqe_needs_user(s->sqe) && !cur_mm) {
+			if (!mmget_not_zero(ctx->sqo_mm)) {
+				ret = -EFAULT;
+			} else {
+				cur_mm = ctx->sqo_mm;;
+				use_mm(ctx->sqo_mm);
+				old_fs = get_fs();
+				set_fs(USER_DS);
+			}
+		}
+
+		if (!ret)
+			ret = __io_submit_sqe(ctx, req, s, false, NULL);
+		if (ret) {
+			io_cqring_add_event(ctx, user_data, ret, 0);
+			io_free_req(req);
+		}
+		if (!async_list)
+			break;
+		if (!list_empty(&req_list)) {
+			req = list_first_entry(&req_list, struct io_kiocb,
+						list);
+			list_del(&req->list);
+			continue;
+		}
+		if (list_empty(&async_list->list))
+			break;
+
+		req = NULL;
+		spin_lock(&async_list->lock);
+		if (list_empty(&async_list->list)) {
+			spin_unlock(&async_list->lock);
+			break;
+		}
+		list_splice_init(&async_list->list, &req_list);
+		spin_unlock(&async_list->lock);
+
+		req = list_first_entry(&req_list, struct io_kiocb, list);
+		list_del(&req->list);
+	} while (req);
+
 	/*
-	 * If we're doing IO to fixed buffers, we don't need to get/set
-	 * user context
+	 * Rare case of racing with a submitter. If we find the count has
+	 * dropped to zero AND we have pending work items, then restart
+	 * the processing. This is a tiny race window.
 	 */
-	needs_user = io_sqe_needs_user(s->sqe);
-	if (needs_user) {
-		if (!mmget_not_zero(ctx->sqo_mm)) {
-			ret = -EFAULT;
-			goto err;
+	ret = atomic_dec_return(&async_list->cnt);
+	while (!ret && !list_empty(&async_list->list)) {
+		spin_lock(&async_list->lock);
+		atomic_inc(&async_list->cnt);
+		list_splice_init(&async_list->list, &req_list);
+		spin_unlock(&async_list->lock);
+
+		if (!list_empty(&req_list)) {
+			req = list_first_entry(&req_list, struct io_kiocb,
+						list);
+			list_del(&req->list);
+			goto restart;
 		}
-		use_mm(ctx->sqo_mm);
-		old_fs = get_fs();
-		set_fs(USER_DS);
+		ret = atomic_dec_return(&async_list->cnt);
 	}
 
-	ret = __io_submit_sqe(ctx, req, s, false, NULL);
-
-	if (needs_user) {
+	if (cur_mm) {
 		set_fs(old_fs);
-		unuse_mm(ctx->sqo_mm);
-		mmput(ctx->sqo_mm);
-	}
-err:
-	if (ret) {
-		io_cqring_add_event(ctx, user_data, ret, 0);
-		io_free_req(req);
+		unuse_mm(cur_mm);
+		mmput(cur_mm);
 	}
 	current->files = old_files;
 }
 
+/*
+ * See if we can piggy back onto previously submitted work, that is still
+ * running. We currently only allow this if the new request is sequential
+ * to the previous one we punted.
+ */
+static bool io_add_to_prev_work(struct async_list *list, struct io_kiocb *req)
+{
+	bool ret = false;
+
+	if (!list)
+		return false;
+	if (!(req->flags & REQ_F_SEQ_PREV))
+		return false;
+	if (!atomic_read(&list->cnt))
+		return false;
+
+	ret = true;
+	spin_lock(&list->lock);
+	list_add_tail(&req->list, &list->list);
+	if (!atomic_read(&list->cnt)) {
+		list_del_init(&req->list);
+		ret = false;
+	}
+	spin_unlock(&list->lock);
+	return ret;
+}
+
 static int io_submit_sqe(struct io_ring_ctx *ctx, struct sqe_submit *s,
 			 struct io_submit_state *state)
 {
@@ -1281,9 +1431,16 @@ static int io_submit_sqe(struct io_ring_ctx *ctx, struct sqe_submit *s,
 
 	ret = __io_submit_sqe(ctx, req, s, true, state);
 	if (ret == -EAGAIN) {
+		struct async_list *list;
+
+		list = io_async_list_from_sqe(ctx, s->sqe);
 		memcpy(&req->submit, s, sizeof(*s));
-		INIT_WORK(&req->work, io_sq_wq_submit_work);
-		queue_work(ctx->sqo_wq, &req->work);
+		if (!io_add_to_prev_work(list, req)) {
+			if (list)
+				atomic_inc(&list->cnt);
+			INIT_WORK(&req->work, io_sq_wq_submit_work);
+			queue_work(ctx->sqo_wq, &req->work);
+		}
 		ret = 0;
 	}
 	if (ret)
-- 
2.17.1

[PATCH 13/18] io_uring: add file set registration

[Jens Axboe]

We normally have to fget/fput for each IO we do on a file. Even with
the batching we do, the cost of the atomic inc/dec of the file usage
count adds up.

This adds IORING_REGISTER_FILES, and IORING_UNREGISTER_FILES opcodes
for the io_uring_register(2) system call. The arguments passed in must
be an array of __s32 holding file descriptors, and nr_args should hold
the number of file descriptors the application wishes to pin for the
duration of the io_uring context (or until IORING_UNREGISTER_FILES is
called).

When used, the application must set IOSQE_FIXED_FILE in the sqe->flags
member. Then, instead of setting sqe->fd to the real fd, it sets sqe->fd
to the index in the array passed in to IORING_REGISTER_FILES.

Files are automatically unregistered when the io_uring context is
torn down. An application need only unregister if it wishes to
register a few set of fds.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c                 | 125 +++++++++++++++++++++++++++++-----
 include/uapi/linux/io_uring.h |   9 ++-
 2 files changed, 116 insertions(+), 18 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 63ad09e7cdc7..86add82e1008 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -100,6 +100,10 @@ struct io_ring_ctx {
 		struct fasync_struct	*cq_fasync;
 	} ____cacheline_aligned_in_smp;
 
+	/* if used, fixed file set */
+	struct file		**user_files;
+	unsigned		nr_user_files;
+
 	/* if used, fixed mapped user buffers */
 	unsigned		nr_user_bufs;
 	struct io_mapped_ubuf	*user_bufs;
@@ -137,6 +141,7 @@ struct io_kiocb {
 #define REQ_F_FORCE_NONBLOCK	1	/* inline submission attempt */
 #define REQ_F_IOPOLL_COMPLETED	2	/* polled IO has completed */
 #define REQ_F_IOPOLL_EAGAIN	4	/* submission got EAGAIN */
+#define REQ_F_FIXED_FILE	8	/* ctx owns file */
 	u64			user_data;
 	u64			res;
 
@@ -359,15 +364,17 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
 		 * Batched puts of the same file, to avoid dirtying the
 		 * file usage count multiple times, if avoidable.
 		 */
-		if (!file) {
-			file = req->rw.ki_filp;
-			file_count = 1;
-		} else if (file == req->rw.ki_filp) {
-			file_count++;
-		} else {
-			fput_many(file, file_count);
-			file = req->rw.ki_filp;
-			file_count = 1;
+		if (!(req->flags & REQ_F_FIXED_FILE)) {
+			if (!file) {
+				file = req->rw.ki_filp;
+				file_count = 1;
+			} else if (file == req->rw.ki_filp) {
+				file_count++;
+			} else {
+				fput_many(file, file_count);
+				file = req->rw.ki_filp;
+				file_count = 1;
+			}
 		}
 
 		if (to_free == ARRAY_SIZE(reqs))
@@ -504,13 +511,19 @@ static void kiocb_end_write(struct kiocb *kiocb)
 	}
 }
 
+static void io_fput(struct io_kiocb *req)
+{
+	if (!(req->flags & REQ_F_FIXED_FILE))
+		fput(req->rw.ki_filp);
+}
+
 static void io_complete_rw(struct kiocb *kiocb, long res, long res2)
 {
 	struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw);
 
 	kiocb_end_write(kiocb);
 
-	fput(kiocb->ki_filp);
+	io_fput(req);
 	io_cqring_add_event(req->ctx, req->user_data, res, 0);
 	io_free_req(req);
 }
@@ -614,7 +627,14 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	struct kiocb *kiocb = &req->rw;
 	int ret;
 
-	kiocb->ki_filp = io_file_get(state, sqe->fd);
+	if (sqe->flags & IOSQE_FIXED_FILE) {
+		if (unlikely(!ctx->user_files || sqe->fd >= ctx->nr_user_files))
+			return -EBADF;
+		kiocb->ki_filp = ctx->user_files[sqe->fd];
+		req->flags |= REQ_F_FIXED_FILE;
+	} else {
+		kiocb->ki_filp = io_file_get(state, sqe->fd);
+	}
 	if (unlikely(!kiocb->ki_filp))
 		return -EBADF;
 	kiocb->ki_pos = sqe->off;
@@ -653,7 +673,8 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	}
 	return 0;
 out_fput:
-	io_file_put(state, kiocb->ki_filp);
+	if (!(sqe->flags & IOSQE_FIXED_FILE))
+		io_file_put(state, kiocb->ki_filp);
 	return ret;
 }
 
@@ -770,7 +791,7 @@ static ssize_t io_read(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	kfree(iovec);
 out_fput:
 	if (unlikely(ret))
-		fput(file);
+		io_fput(req);
 	return ret;
 }
 
@@ -825,7 +846,7 @@ static ssize_t io_write(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	kfree(iovec);
 out_fput:
 	if (unlikely(ret))
-		fput(file);
+		io_fput(req);
 	return ret;
 }
 
@@ -863,14 +884,23 @@ static int io_fsync(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	if (unlikely(sqe->fsync_flags & ~IORING_FSYNC_DATASYNC))
 		return -EINVAL;
 
-	file = fget(sqe->fd);
+	if (sqe->flags & IOSQE_FIXED_FILE) {
+		if (unlikely(!ctx->user_files || sqe->fd >= ctx->nr_user_files))
+			return -EBADF;
+		file = ctx->user_files[sqe->fd];
+	} else {
+		file = fget(sqe->fd);
+	}
+
 	if (unlikely(!file))
 		return -EBADF;
 
 	ret = vfs_fsync_range(file, sqe->off, end > 0 ? end : LLONG_MAX,
 			sqe->fsync_flags & IORING_FSYNC_DATASYNC);
 
-	fput(file);
+	if (!(sqe->flags & IOSQE_FIXED_FILE))
+		fput(file);
+
 	io_cqring_add_event(ctx, sqe->user_data, ret, 0);
 	io_free_req(req);
 	return 0;
@@ -988,7 +1018,7 @@ static int io_submit_sqe(struct io_ring_ctx *ctx, struct sqe_submit *s,
 	ssize_t ret;
 
 	/* enforce forwards compatibility on users */
-	if (unlikely(s->sqe->flags))
+	if (unlikely(s->sqe->flags & ~IOSQE_FIXED_FILE))
 		return -EINVAL;
 
 	req = io_get_req(ctx, state);
@@ -1173,6 +1203,57 @@ static int __io_uring_enter(struct io_ring_ctx *ctx, unsigned to_submit,
 	return ret;
 }
 
+static int io_sqe_files_unregister(struct io_ring_ctx *ctx)
+{
+	int i;
+
+	if (!ctx->user_files)
+		return -ENXIO;
+
+	for (i = 0; i < ctx->nr_user_files; i++)
+		fput(ctx->user_files[i]);
+
+	kfree(ctx->user_files);
+	ctx->user_files = NULL;
+	ctx->nr_user_files = 0;
+	return 0;
+}
+
+static int io_sqe_files_register(struct io_ring_ctx *ctx, void __user *arg,
+				 unsigned nr_args)
+{
+	__s32 __user *fds = (__s32 __user *) arg;
+	int fd, i, ret = 0;
+
+	if (ctx->user_files)
+		return -EBUSY;
+	if (!nr_args)
+		return -EINVAL;
+
+	ctx->user_files = kcalloc(nr_args, sizeof(struct file *), GFP_KERNEL);
+	if (!ctx->user_files)
+		return -ENOMEM;
+
+	for (i = 0; i < nr_args; i++) {
+		ret = -EFAULT;
+		if (copy_from_user(&fd, &fds[i], sizeof(fd)))
+			break;
+
+		ctx->user_files[i] = fget(fd);
+
+		ret = -EBADF;
+		if (!ctx->user_files[i])
+			break;
+		ctx->nr_user_files++;
+		ret = 0;
+	}
+
+	if (ret)
+		io_sqe_files_unregister(ctx);
+
+	return ret;
+}
+
 static int io_sq_offload_start(struct io_ring_ctx *ctx)
 {
 	int ret;
@@ -1468,6 +1549,7 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx)
 	io_sq_offload_stop(ctx);
 	io_iopoll_reap_events(ctx);
 	io_free_scq_urings(ctx);
+	io_sqe_files_unregister(ctx);
 	io_sqe_buffer_unregister(ctx);
 	percpu_ref_exit(&ctx->refs);
 	io_unaccount_mem(ctx, ring_pages(ctx->sq_entries, ctx->cq_entries));
@@ -1780,6 +1862,15 @@ static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
 			break;
 		ret = io_sqe_buffer_unregister(ctx);
 		break;
+	case IORING_REGISTER_FILES:
+		ret = io_sqe_files_register(ctx, arg, nr_args);
+		break;
+	case IORING_UNREGISTER_FILES:
+		ret = -EINVAL;
+		if (arg || nr_args)
+			break;
+		ret = io_sqe_files_unregister(ctx);
+		break;
 	default:
 		ret = -EINVAL;
 		break;
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 03ce7133c3b2..8323320077ec 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -18,7 +18,7 @@
  */
 struct io_uring_sqe {
 	__u8	opcode;		/* type of operation for this sqe */
-	__u8	flags;		/* as of now unused */
+	__u8	flags;		/* IOSQE_ flags */
 	__u16	ioprio;		/* ioprio for the request */
 	__s32	fd;		/* file descriptor to do IO on */
 	__u64	off;		/* offset into file */
@@ -35,6 +35,11 @@ struct io_uring_sqe {
 	};
 };
 
+/*
+ * sqe->flags
+ */
+#define IOSQE_FIXED_FILE	(1 << 0)	/* use fixed fileset */
+
 /*
  * io_uring_setup() flags
  */
@@ -114,5 +119,7 @@ struct io_uring_params {
  */
 #define IORING_REGISTER_BUFFERS		0
 #define IORING_UNREGISTER_BUFFERS	1
+#define IORING_REGISTER_FILES		2
+#define IORING_UNREGISTER_FILES		3
 
 #endif
-- 
2.17.1

[PATCH 13/13] io_uring: add io_uring_event cache hit information

[Jens Axboe]

Add hint on whether a read was served out of the page cache, or if it
hit media. This is useful for buffered async IO, O_DIRECT reads would
never have this set (for obvious reasons).

If the read hit page cache, cqe->flags will have IOCQE_FLAG_CACHEHIT
set.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c                 | 7 ++++++-
 include/uapi/linux/io_uring.h | 5 +++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index aa903fa902d5..a40b1af356e0 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -561,11 +561,16 @@ static void io_fput(struct io_kiocb *req)
 static void io_complete_rw(struct kiocb *kiocb, long res, long res2)
 {
 	struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw);
+	unsigned ev_flags = 0;
 
 	kiocb_end_write(kiocb);
 
 	io_fput(req);
-	io_cqring_add_event(req->ctx, req->user_data, res, 0);
+
+	if (res > 0 && (req->flags & REQ_F_FORCE_NONBLOCK))
+		ev_flags = IOCQE_FLAG_CACHEHIT;
+
+	io_cqring_add_event(req->ctx, req->user_data, res, ev_flags);
 	io_free_req(req);
 }
 
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 60b52c551c87..3b8d623031ad 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -71,6 +71,11 @@ struct io_uring_cqe {
 	__u32	flags;
 };
 
+/*
+ * io_uring_event->flags
+ */
+#define IOCQE_FLAG_CACHEHIT	(1 << 0)	/* IO did not hit media */
+
 /*
  * Magic offsets for the application to mmap the data it needs
  */
-- 
2.17.1

[PATCH 14/18] io_uring: add submission polling

[Jens Axboe]

This enables an application to do IO, without ever entering the kernel.
By using the SQ ring to fill in new sqes and watching for completions
on the CQ ring, we can submit and reap IOs without doing a single system
call. The kernel side thread will poll for new submissions, and in case
of HIPRI/polled IO, it'll also poll for completions.

Proof of concept. If the thread has been idle for 1 second, it will set
sq_ring->flags |= IORING_SQ_NEED_WAKEUP. The application will have to
call io_uring_enter() to start things back up again. If IO is kept busy,
that will never be needed. Basically an application that has this
feature enabled will guard it's io_uring_enter(2) call with:

read_barrier();
if (*sq_ring->flags & IORING_SQ_NEED_WAKEUP)
	io_uring_enter(fd, to_submit, 0, 0);

instead of calling it unconditionally.

Improvements:

1) Maybe have smarter backoff. Busy loop for X time, then go to
   monitor/mwait, finally the schedule we have now after an idle
   second. Might not be worth the complexity.

2) Probably want the application to pass in the appropriate grace
   period, not hard code it at 1 second.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c                 | 219 +++++++++++++++++++++++++++++++++-
 include/uapi/linux/io_uring.h |  10 +-
 2 files changed, 222 insertions(+), 7 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 86add82e1008..2deda7b1b3dd 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -24,6 +24,7 @@
 #include <linux/percpu.h>
 #include <linux/slab.h>
 #include <linux/workqueue.h>
+#include <linux/kthread.h>
 #include <linux/blkdev.h>
 #include <linux/bvec.h>
 #include <linux/anon_inodes.h>
@@ -87,8 +88,10 @@ struct io_ring_ctx {
 
 	/* IO offload */
 	struct workqueue_struct	*sqo_wq;
+	struct task_struct	*sqo_thread;	/* if using sq thread polling */
 	struct mm_struct	*sqo_mm;
 	struct files_struct	*sqo_files;
+	wait_queue_head_t	sqo_wait;
 
 	struct {
 		/* CQ ring */
@@ -264,6 +267,9 @@ static void __io_cqring_add_event(struct io_ring_ctx *ctx, u64 ki_user_data,
 
 	if (waitqueue_active(&ctx->wait))
 		wake_up(&ctx->wait);
+	if ((ctx->flags & IORING_SETUP_SQPOLL) &&
+	    waitqueue_active(&ctx->sqo_wait))
+		wake_up(&ctx->sqo_wait);
 }
 
 static void io_cqring_add_event(struct io_ring_ctx *ctx, u64 ki_user_data,
@@ -1106,6 +1112,168 @@ static bool io_get_sqring(struct io_ring_ctx *ctx, struct sqe_submit *s)
 	return false;
 }
 
+static int io_submit_sqes(struct io_ring_ctx *ctx, struct sqe_submit *sqes,
+			  unsigned int nr, bool mm_fault)
+{
+	struct io_submit_state state, *statep = NULL;
+	int ret, i, submitted = 0;
+
+	if (nr > IO_PLUG_THRESHOLD) {
+		io_submit_state_start(&state, ctx, nr);
+		statep = &state;
+	}
+
+	for (i = 0; i < nr; i++) {
+		if (unlikely(mm_fault))
+			ret = -EFAULT;
+		else
+			ret = io_submit_sqe(ctx, &sqes[i], statep);
+		if (!ret) {
+			submitted++;
+			continue;
+		}
+
+		io_cqring_add_event(ctx, sqes[i].sqe->user_data, ret, 0);
+	}
+
+	if (statep)
+		io_submit_state_end(&state);
+
+	return submitted;
+}
+
+static int io_sq_thread(void *data)
+{
+	struct sqe_submit sqes[IO_IOPOLL_BATCH];
+	struct io_ring_ctx *ctx = data;
+	struct mm_struct *cur_mm = NULL;
+	struct files_struct *old_files;
+	mm_segment_t old_fs;
+	DEFINE_WAIT(wait);
+	unsigned inflight;
+	unsigned long timeout;
+
+	old_files = current->files;
+	current->files = ctx->sqo_files;
+
+	old_fs = get_fs();
+	set_fs(USER_DS);
+
+	timeout = inflight = 0;
+	while (!kthread_should_stop()) {
+		bool all_fixed, mm_fault = false;
+		int i;
+
+		if (inflight) {
+			unsigned int nr_events = 0;
+
+			/*
+			 * Normal IO, just pretend everything completed.
+			 * We don't have to poll completions for that.
+			 */
+			if (ctx->flags & IORING_SETUP_IOPOLL) {
+				/*
+				 * App should not use IORING_ENTER_GETEVENTS
+				 * with thread polling, but if it does, then
+				 * ensure we are mutually exclusive.
+				 */
+				if (mutex_trylock(&ctx->uring_lock)) {
+					io_iopoll_check(ctx, &nr_events, 0);
+					mutex_unlock(&ctx->uring_lock);
+				}
+			} else {
+				nr_events = inflight;
+			}
+
+			inflight -= nr_events;
+			if (!inflight)
+				timeout = jiffies + HZ;
+		}
+
+		if (!io_get_sqring(ctx, &sqes[0])) {
+			/*
+			 * We're polling, let us spin for a second without
+			 * work before going to sleep.
+			 */
+			if (inflight || !time_after(jiffies, timeout)) {
+				cpu_relax();
+				continue;
+			}
+
+			/*
+			 * Drop cur_mm before scheduling, we can't hold it for
+			 * long periods (or over schedule()). Do this before
+			 * adding ourselves to the waitqueue, as the unuse/drop
+			 * may sleep.
+			 */
+			if (cur_mm) {
+				unuse_mm(cur_mm);
+				mmput(cur_mm);
+				cur_mm = NULL;
+			}
+
+			prepare_to_wait(&ctx->sqo_wait, &wait,
+						TASK_INTERRUPTIBLE);
+
+			/* Tell userspace we may need a wakeup call */
+			ctx->sq_ring->flags |= IORING_SQ_NEED_WAKEUP;
+			smp_wmb();
+
+			if (!io_get_sqring(ctx, &sqes[0])) {
+				if (kthread_should_park())
+					kthread_parkme();
+				if (kthread_should_stop()) {
+					finish_wait(&ctx->sqo_wait, &wait);
+					break;
+				}
+				if (signal_pending(current))
+					flush_signals(current);
+				schedule();
+				finish_wait(&ctx->sqo_wait, &wait);
+
+				ctx->sq_ring->flags &= ~IORING_SQ_NEED_WAKEUP;
+				smp_wmb();
+				continue;
+			}
+			finish_wait(&ctx->sqo_wait, &wait);
+
+			ctx->sq_ring->flags &= ~IORING_SQ_NEED_WAKEUP;
+			smp_wmb();
+		}
+
+		i = 0;
+		all_fixed = true;
+		do {
+			if (all_fixed && io_sqe_needs_user(sqes[i].sqe))
+				all_fixed = false;
+
+			i++;
+			if (i == ARRAY_SIZE(sqes))
+				break;
+		} while (io_get_sqring(ctx, &sqes[i]));
+
+		io_commit_sqring(ctx);
+
+		/* Unless all new commands are FIXED regions, grab mm */
+		if (!all_fixed && !cur_mm) {
+			mm_fault = !mmget_not_zero(ctx->sqo_mm);
+			if (!mm_fault) {
+				use_mm(ctx->sqo_mm);
+				cur_mm = ctx->sqo_mm;
+			}
+		}
+
+		inflight += io_submit_sqes(ctx, sqes, i, mm_fault);
+	}
+	current->files = old_files;
+	set_fs(old_fs);
+	if (cur_mm) {
+		unuse_mm(cur_mm);
+		mmput(cur_mm);
+	}
+	return 0;
+}
+
 static int io_ring_submit(struct io_ring_ctx *ctx, unsigned int to_submit)
 {
 	struct io_submit_state state, *statep = NULL;
@@ -1179,9 +1347,14 @@ static int __io_uring_enter(struct io_ring_ctx *ctx, unsigned to_submit,
 	int ret = 0;
 
 	if (to_submit) {
-		ret = io_ring_submit(ctx, to_submit);
-		if (ret < 0)
-			return ret;
+		if (ctx->flags & IORING_SETUP_SQPOLL) {
+			wake_up(&ctx->sqo_wait);
+			ret = to_submit;
+		} else {
+			ret = io_ring_submit(ctx, to_submit);
+			if (ret < 0)
+				return ret;
+		}
 	}
 	if (flags & IORING_ENTER_GETEVENTS) {
 		unsigned nr_events = 0;
@@ -1254,10 +1427,12 @@ static int io_sqe_files_register(struct io_ring_ctx *ctx, void __user *arg,
 	return ret;
 }
 
-static int io_sq_offload_start(struct io_ring_ctx *ctx)
+static int io_sq_offload_start(struct io_ring_ctx *ctx,
+			       struct io_uring_params *p)
 {
 	int ret;
 
+	init_waitqueue_head(&ctx->sqo_wait);
 	ctx->sqo_mm = current->mm;
 
 	/*
@@ -1270,6 +1445,27 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx)
 	if (!ctx->sqo_files)
 		goto err;
 
+	if (ctx->flags & IORING_SETUP_SQPOLL) {
+		if (p->flags & IORING_SETUP_SQ_AFF) {
+			ctx->sqo_thread = kthread_create_on_cpu(io_sq_thread,
+							ctx, p->sq_thread_cpu,
+							"io_uring-sq");
+		} else {
+			ctx->sqo_thread = kthread_create(io_sq_thread, ctx,
+							"io_uring-sq");
+		}
+		if (IS_ERR(ctx->sqo_thread)) {
+			ret = PTR_ERR(ctx->sqo_thread);
+			ctx->sqo_thread = NULL;
+			goto err;
+		}
+		wake_up_process(ctx->sqo_thread);
+	} else if (p->flags & IORING_SETUP_SQ_AFF) {
+		/* Can't have SQ_AFF without SQPOLL */
+		ret = -EINVAL;
+		goto err;
+	}
+
 	/* Do QD, or 2 * CPUS, whatever is smallest */
 	ctx->sqo_wq = alloc_workqueue("io_ring-wq", WQ_UNBOUND | WQ_FREEZABLE,
 			min(ctx->sq_entries - 1, 2 * num_online_cpus()));
@@ -1280,6 +1476,11 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx)
 
 	return 0;
 err:
+	if (ctx->sqo_thread) {
+		kthread_park(ctx->sqo_thread);
+		kthread_stop(ctx->sqo_thread);
+		ctx->sqo_thread = NULL;
+	}
 	if (ctx->sqo_files)
 		ctx->sqo_files = NULL;
 	ctx->sqo_mm = NULL;
@@ -1288,6 +1489,11 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx)
 
 static void io_sq_offload_stop(struct io_ring_ctx *ctx)
 {
+	if (ctx->sqo_thread) {
+		kthread_park(ctx->sqo_thread);
+		kthread_stop(ctx->sqo_thread);
+		ctx->sqo_thread = NULL;
+	}
 	if (ctx->sqo_wq) {
 		destroy_workqueue(ctx->sqo_wq);
 		ctx->sqo_wq = NULL;
@@ -1780,7 +1986,7 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p,
 	if (ret)
 		goto err;
 
-	ret = io_sq_offload_start(ctx);
+	ret = io_sq_offload_start(ctx, p);
 	if (ret)
 		goto err;
 
@@ -1815,7 +2021,8 @@ static long io_uring_setup(u32 entries, struct io_uring_params __user *params,
 			return -EINVAL;
 	}
 
-	if (p.flags & ~IORING_SETUP_IOPOLL)
+	if (p.flags & ~(IORING_SETUP_IOPOLL | IORING_SETUP_SQPOLL |
+			IORING_SETUP_SQ_AFF))
 		return -EINVAL;
 
 	ret = io_uring_create(entries, &p, compat);
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 8323320077ec..37c7402be9ca 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -44,6 +44,8 @@ struct io_uring_sqe {
  * io_uring_setup() flags
  */
 #define IORING_SETUP_IOPOLL	(1 << 0)	/* io_context is polled */
+#define IORING_SETUP_SQPOLL	(1 << 1)	/* SQ poll thread */
+#define IORING_SETUP_SQ_AFF	(1 << 2)	/* sq_thread_cpu is valid */
 
 #define IORING_OP_NOP		0
 #define IORING_OP_READV		1
@@ -87,6 +89,11 @@ struct io_sqring_offsets {
 	__u32 resv[3];
 };
 
+/*
+ * sq_ring->flags
+ */
+#define IORING_SQ_NEED_WAKEUP	(1 << 0) /* needs io_uring_enter wakeup */
+
 struct io_cqring_offsets {
 	__u32 head;
 	__u32 tail;
@@ -109,7 +116,8 @@ struct io_uring_params {
 	__u32 sq_entries;
 	__u32 cq_entries;
 	__u32 flags;
-	__u16 resv[10];
+	__u16 sq_thread_cpu;
+	__u16 resv[9];
 	struct io_sqring_offsets sq_off;
 	struct io_cqring_offsets cq_off;
 };
-- 
2.17.1

[PATCH 15/18] io_uring: add io_kiocb ref count

[Jens Axboe]

We'll use this for the POLL implementation. Regular requests will
NOT be using references, so initialize it to 0. Any real use of
the io_kiocb ref will initialize it to at least 2.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 2deda7b1b3dd..c10653be39c0 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -141,6 +141,7 @@ struct io_kiocb {
 	struct io_ring_ctx	*ctx;
 	struct list_head	list;
 	unsigned int		flags;
+	refcount_t		refs;
 #define REQ_F_FORCE_NONBLOCK	1	/* inline submission attempt */
 #define REQ_F_IOPOLL_COMPLETED	2	/* polled IO has completed */
 #define REQ_F_IOPOLL_EAGAIN	4	/* submission got EAGAIN */
@@ -322,6 +323,7 @@ static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx,
 	if (req) {
 		req->ctx = ctx;
 		req->flags = 0;
+		refcount_set(&req->refs, 0);
 		return req;
 	}
 
@@ -341,8 +343,10 @@ static void io_free_req_many(struct io_ring_ctx *ctx, void **reqs, int *nr)
 
 static void io_free_req(struct io_kiocb *req)
 {
-	io_ring_drop_ctx_refs(req->ctx, 1);
-	kmem_cache_free(req_cachep, req);
+	if (!refcount_read(&req->refs) || refcount_dec_and_test(&req->refs)) {
+		io_ring_drop_ctx_refs(req->ctx, 1);
+		kmem_cache_free(req_cachep, req);
+	}
 }
 
 /*
-- 
2.17.1

[PATCH 16/18] io_uring: add support for IORING_OP_POLL

[Jens Axboe]

This is basically a direct port of bfe4037e722e, which implements a
one-shot poll command through aio. Description below is based on that
commit as well. However, instead of adding a POLL command and relying
on io_cancel(2) to remove it, we mimic the epoll(2) interface of
having a command to add a poll notification, IORING_OP_POLL_ADD,
and one to remove it again, IORING_OP_POLL_REMOVE.

To poll for a file descriptor the application should submit an sqe of
type IORING_OP_POLL. It will poll the fd for the events specified in the
poll_events field.

Unlike poll or epoll without EPOLLONESHOT this interface always works in
one shot mode, that is once the sqe is completed, it will have to be
resubmitted.

Based-on-code-from: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c                 | 245 ++++++++++++++++++++++++++++++++++
 include/uapi/linux/io_uring.h |   3 +
 2 files changed, 248 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index c10653be39c0..fe75931d7df5 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -124,6 +124,7 @@ struct io_ring_ctx {
 		spinlock_t		completion_lock;
 		unsigned		poll_multi_file;
 		struct list_head	poll_list;
+		struct list_head	cancel_list;
 	} ____cacheline_aligned_in_smp;
 };
 
@@ -132,9 +133,19 @@ struct sqe_submit {
 	unsigned index;
 };
 
+struct io_poll_iocb {
+	struct file *file;
+	struct wait_queue_head *head;
+	__poll_t events;
+	bool woken;
+	bool canceled;
+	struct wait_queue_entry wait;
+};
+
 struct io_kiocb {
 	union {
 		struct kiocb		rw;
+		struct io_poll_iocb	poll;
 		struct sqe_submit	submit;
 	};
 
@@ -206,6 +217,7 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 	init_waitqueue_head(&ctx->wait);
 	spin_lock_init(&ctx->completion_lock);
 	INIT_LIST_HEAD(&ctx->poll_list);
+	INIT_LIST_HEAD(&ctx->cancel_list);
 	return ctx;
 }
 
@@ -916,6 +928,232 @@ static int io_fsync(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	return 0;
 }
 
+static void io_poll_remove_one(struct io_kiocb *req)
+{
+	struct io_poll_iocb *poll = &req->poll;
+
+	spin_lock(&poll->head->lock);
+	WRITE_ONCE(poll->canceled, true);
+	if (!list_empty(&poll->wait.entry)) {
+		list_del_init(&poll->wait.entry);
+		queue_work(req->ctx->sqo_wq, &req->work);
+	}
+	spin_unlock(&poll->head->lock);
+
+	list_del_init(&req->list);
+}
+
+static void io_poll_remove_all(struct io_ring_ctx *ctx)
+{
+	struct io_kiocb *req;
+
+	spin_lock_irq(&ctx->completion_lock);
+	while (!list_empty(&ctx->cancel_list)) {
+		req = list_first_entry(&ctx->cancel_list, struct io_kiocb,list);
+		io_poll_remove_one(req);
+	}
+	spin_unlock_irq(&ctx->completion_lock);
+}
+
+/*
+ * Find a running poll command that matches one specified in sqe->addr,
+ * and remove it if found.
+ */
+static int io_poll_remove(struct io_kiocb *req, const struct io_uring_sqe *sqe)
+{
+	struct io_ring_ctx *ctx = req->ctx;
+	struct io_kiocb *poll_req, *next;
+	int ret = -ENOENT;
+
+	if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
+		return -EINVAL;
+	if (sqe->ioprio || sqe->off || sqe->len || sqe->buf_index ||
+	    sqe->poll_events)
+		return -EINVAL;
+
+	spin_lock_irq(&ctx->completion_lock);
+	list_for_each_entry_safe(poll_req, next, &ctx->cancel_list, list) {
+		if (sqe->addr == poll_req->user_data) {
+			io_poll_remove_one(poll_req);
+			ret = 0;
+			break;
+		}
+	}
+	spin_unlock_irq(&ctx->completion_lock);
+
+	io_cqring_add_event(req->ctx, sqe->user_data, ret, 0);
+	io_free_req(req);
+	return 0;
+}
+
+static void io_poll_complete(struct io_kiocb *req, __poll_t mask)
+{
+	io_cqring_add_event(req->ctx, req->user_data, mangle_poll(mask), 0);
+	io_fput(req);
+	io_free_req(req);
+}
+
+static void io_poll_complete_work(struct work_struct *work)
+{
+	struct io_kiocb *req = container_of(work, struct io_kiocb, work);
+	struct io_poll_iocb *poll = &req->poll;
+	struct poll_table_struct pt = { ._key = poll->events };
+	struct io_ring_ctx *ctx = req->ctx;
+	__poll_t mask = 0;
+
+	if (!READ_ONCE(poll->canceled))
+		mask = vfs_poll(poll->file, &pt) & poll->events;
+
+	/*
+	 * Note that ->ki_cancel callers also delete iocb from active_reqs after
+	 * calling ->ki_cancel.  We need the ctx_lock roundtrip here to
+	 * synchronize with them.  In the cancellation case the list_del_init
+	 * itself is not actually needed, but harmless so we keep it in to
+	 * avoid further branches in the fast path.
+	 */
+	spin_lock_irq(&ctx->completion_lock);
+	if (!mask && !READ_ONCE(poll->canceled)) {
+		add_wait_queue(poll->head, &poll->wait);
+		spin_unlock_irq(&ctx->completion_lock);
+		return;
+	}
+	list_del_init(&req->list);
+	spin_unlock_irq(&ctx->completion_lock);
+
+	io_poll_complete(req, mask);
+}
+
+static int io_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
+			void *key)
+{
+	struct io_poll_iocb *poll = container_of(wait, struct io_poll_iocb,
+							wait);
+	struct io_kiocb *req = container_of(poll, struct io_kiocb, poll);
+	struct io_ring_ctx *ctx = req->ctx;
+	__poll_t mask = key_to_poll(key);
+
+	poll->woken = true;
+
+	/* for instances that support it check for an event match first: */
+	if (mask) {
+		if (!(mask & poll->events))
+			return 0;
+
+		/* try to complete the iocb inline if we can: */
+		if (spin_trylock(&ctx->completion_lock)) {
+			list_del(&req->list);
+			spin_unlock(&ctx->completion_lock);
+
+			list_del_init(&poll->wait.entry);
+			io_poll_complete(req, mask);
+			return 1;
+		}
+	}
+
+	list_del_init(&poll->wait.entry);
+	queue_work(ctx->sqo_wq, &req->work);
+	return 1;
+}
+
+struct io_poll_table {
+	struct poll_table_struct pt;
+	struct io_kiocb *req;
+	int error;
+};
+
+static void io_poll_queue_proc(struct file *file, struct wait_queue_head *head,
+			       struct poll_table_struct *p)
+{
+	struct io_poll_table *pt = container_of(p, struct io_poll_table, pt);
+
+	if (unlikely(pt->req->poll.head)) {
+		pt->error = -EINVAL;
+		return;
+	}
+
+	pt->error = 0;
+	pt->req->poll.head = head;
+	add_wait_queue(head, &pt->req->poll.wait);
+}
+
+static int io_poll_add(struct io_kiocb *req, const struct io_uring_sqe *sqe)
+{
+	struct io_poll_iocb *poll = &req->poll;
+	struct io_ring_ctx *ctx = req->ctx;
+	struct io_poll_table ipt;
+	__poll_t mask;
+
+	if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
+		return -EINVAL;
+	if (sqe->addr || sqe->ioprio || sqe->off || sqe->len || sqe->buf_index)
+		return -EINVAL;
+
+	INIT_WORK(&req->work, io_poll_complete_work);
+	poll->events = demangle_poll(sqe->poll_events) | EPOLLERR | EPOLLHUP;
+
+	if (sqe->flags & IOSQE_FIXED_FILE) {
+		if (unlikely(!ctx->user_files || sqe->fd >= ctx->nr_user_files))
+			return -EBADF;
+		poll->file = ctx->user_files[sqe->fd];
+		req->flags |= REQ_F_FIXED_FILE;
+	} else {
+		poll->file = fget(sqe->fd);
+	}
+	if (unlikely(!poll->file))
+		return -EBADF;
+
+	poll->head = NULL;
+	poll->woken = false;
+	poll->canceled = false;
+
+	ipt.pt._qproc = io_poll_queue_proc;
+	ipt.pt._key = poll->events;
+	ipt.req = req;
+	ipt.error = -EINVAL; /* same as no support for IOCB_CMD_POLL */
+
+	/* initialized the list so that we can do list_empty checks */
+	INIT_LIST_HEAD(&poll->wait.entry);
+	init_waitqueue_func_entry(&poll->wait, io_poll_wake);
+
+	/* one for removal from waitqueue, one for this function */
+	refcount_set(&req->refs, 2);
+
+	mask = vfs_poll(poll->file, &ipt.pt) & poll->events;
+	if (unlikely(!poll->head)) {
+		/* we did not manage to set up a waitqueue, done */
+		goto out;
+	}
+
+	spin_lock_irq(&ctx->completion_lock);
+	spin_lock(&poll->head->lock);
+	if (poll->woken) {
+		/* wake_up context handles the rest */
+		mask = 0;
+		ipt.error = 0;
+	} else if (mask || ipt.error) {
+		/* if we get an error or a mask we are done */
+		WARN_ON_ONCE(list_empty(&poll->wait.entry));
+		list_del_init(&poll->wait.entry);
+	} else {
+		/* actually waiting for an event */
+		list_add_tail(&req->list, &ctx->cancel_list);
+	}
+	spin_unlock(&poll->head->lock);
+	spin_unlock_irq(&ctx->completion_lock);
+
+out:
+	if (unlikely(ipt.error)) {
+		if (!(sqe->flags & IOSQE_FIXED_FILE))
+			fput(poll->file);
+		return ipt.error;
+	}
+
+	if (mask)
+		io_poll_complete(req, mask);
+	io_free_req(req);
+	return 0;
+}
+
 static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 			   struct sqe_submit *s, bool force_nonblock,
 			   struct io_submit_state *state)
@@ -951,6 +1189,12 @@ static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 	case IORING_OP_FSYNC:
 		ret = io_fsync(req, sqe, force_nonblock);
 		break;
+	case IORING_OP_POLL_ADD:
+		ret = io_poll_add(req, sqe);
+		break;
+	case IORING_OP_POLL_REMOVE:
+		ret = io_poll_remove(req, sqe);
+		break;
 	default:
 		ret = -EINVAL;
 		break;
@@ -1794,6 +2038,7 @@ static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
 	percpu_ref_kill(&ctx->refs);
 	mutex_unlock(&ctx->uring_lock);
 
+	io_poll_remove_all(ctx);
 	io_iopoll_reap_events(ctx);
 	wait_for_completion(&ctx->ctx_done);
 	io_ring_ctx_free(ctx);
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 37c7402be9ca..60b52c551c87 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -27,6 +27,7 @@ struct io_uring_sqe {
 	union {
 		__kernel_rwf_t	rw_flags;
 		__u32		fsync_flags;
+		__u16		poll_events;
 	};
 	__u64	user_data;	/* data to be passed back at completion time */
 	union {
@@ -53,6 +54,8 @@ struct io_uring_sqe {
 #define IORING_OP_FSYNC		3
 #define IORING_OP_READ_FIXED	4
 #define IORING_OP_WRITE_FIXED	5
+#define IORING_OP_POLL_ADD	6
+#define IORING_OP_POLL_REMOVE	7
 
 /*
  * sqe->fsync_flags
-- 
2.17.1

[PATCH 17/18] io_uring: allow workqueue item to handle multiple buffered requests

[Jens Axboe]

Right now we punt any buffered request that ends up triggering an
-EAGAIN to an async workqueue. This works fine in terms of providing
async execution of them, but it also can create quite a lot of work
queue items. For sequentially buffered IO, it's advantageous to
serialize the issue of them. For reads, the first one will trigger a
read-ahead, and subsequent request merely end up waiting on later pages
to complete. For writes, devices usually respond better to streamed
sequential writes.

Add state to track the last buffered request we punted to a work queue,
and if the next one is sequential to the previous, attempt to get the
previous work item to handle it. We limit the number of sequential
add-ons to the a multiple (8) of the max read-ahead size of the file.
This should be a good number for both reads and wries, as it defines the
max IO size the device can do directly.

This drastically cuts down on the number of context switches we need to
handle buffered sequential IO, and a basic test case of copying a big
file with io_uring sees a 5x speedup.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c | 231 ++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 194 insertions(+), 37 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index fe75931d7df5..aa903fa902d5 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -68,6 +68,16 @@ struct io_mapped_ubuf {
 	unsigned int	nr_bvecs;
 };
 
+struct async_list {
+	spinlock_t		lock;
+	atomic_t		cnt;
+	struct list_head	list;
+
+	struct file		*file;
+	off_t			io_end;
+	size_t			io_pages;
+};
+
 struct io_ring_ctx {
 	struct {
 		struct percpu_ref	refs;
@@ -126,6 +136,8 @@ struct io_ring_ctx {
 		struct list_head	poll_list;
 		struct list_head	cancel_list;
 	} ____cacheline_aligned_in_smp;
+
+	struct async_list	pending_async[2];
 };
 
 struct sqe_submit {
@@ -157,6 +169,7 @@ struct io_kiocb {
 #define REQ_F_IOPOLL_COMPLETED	2	/* polled IO has completed */
 #define REQ_F_IOPOLL_EAGAIN	4	/* submission got EAGAIN */
 #define REQ_F_FIXED_FILE	8	/* ctx owns file */
+#define REQ_F_SEQ_PREV		16	/* sequential with previous */
 	u64			user_data;
 	u64			res;
 
@@ -200,6 +213,7 @@ static void io_ring_ctx_ref_free(struct percpu_ref *ref)
 static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 {
 	struct io_ring_ctx *ctx;
+	int i;
 
 	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
 	if (!ctx)
@@ -215,6 +229,11 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 	init_completion(&ctx->ctx_done);
 	mutex_init(&ctx->uring_lock);
 	init_waitqueue_head(&ctx->wait);
+	for (i = 0; i < ARRAY_SIZE(ctx->pending_async); i++) {
+		spin_lock_init(&ctx->pending_async[i].lock);
+		INIT_LIST_HEAD(&ctx->pending_async[i].list);
+		atomic_set(&ctx->pending_async[i].cnt, 0);
+	}
 	spin_lock_init(&ctx->completion_lock);
 	INIT_LIST_HEAD(&ctx->poll_list);
 	INIT_LIST_HEAD(&ctx->cancel_list);
@@ -774,6 +793,39 @@ static int io_import_iovec(struct io_ring_ctx *ctx, int rw,
 	return import_iovec(rw, buf, sqe->len, UIO_FASTIOV, iovec, iter);
 }
 
+static void io_async_list_note(int rw, struct io_kiocb *req, size_t len)
+{
+	struct async_list *async_list = &req->ctx->pending_async[rw];
+	struct kiocb *kiocb = &req->rw;
+	struct file *filp = kiocb->ki_filp;
+	off_t io_end = kiocb->ki_pos + len;
+
+	if (filp == async_list->file && kiocb->ki_pos == async_list->io_end) {
+		unsigned long max_pages;
+
+		/* Use 8x RA size as a decent limiter for both reads/writes */
+		max_pages = filp->f_ra.ra_pages;
+		if (!max_pages)
+			max_pages = VM_MAX_READAHEAD >> (PAGE_SHIFT - 10);
+		max_pages *= 8;
+
+		len >>= PAGE_SHIFT;
+		if (async_list->io_pages + len <= max_pages) {
+			req->flags |= REQ_F_SEQ_PREV;
+			async_list->io_pages += len;
+		} else {
+			io_end = 0;
+			async_list->io_pages = 0;
+		}
+	}
+
+	if (async_list->file != filp) {
+		async_list->io_pages = 0;
+		async_list->file = filp;
+	}
+	async_list->io_end = io_end;
+}
+
 static ssize_t io_read(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 		       bool force_nonblock, struct io_submit_state *state)
 {
@@ -781,6 +833,7 @@ static ssize_t io_read(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	struct kiocb *kiocb = &req->rw;
 	struct iov_iter iter;
 	struct file *file;
+	size_t iov_count;
 	ssize_t ret;
 
 	ret = io_prep_rw(req, sqe, force_nonblock, state);
@@ -799,16 +852,19 @@ static ssize_t io_read(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	if (ret)
 		goto out_fput;
 
-	ret = rw_verify_area(READ, file, &kiocb->ki_pos, iov_iter_count(&iter));
+	iov_count = iov_iter_count(&iter);
+	ret = rw_verify_area(READ, file, &kiocb->ki_pos, iov_count);
 	if (!ret) {
 		ssize_t ret2;
 
 		/* Catch -EAGAIN return for forced non-blocking submission */
 		ret2 = call_read_iter(file, kiocb, &iter);
-		if (!force_nonblock || ret2 != -EAGAIN)
+		if (!force_nonblock || ret2 != -EAGAIN) {
 			io_rw_done(kiocb, ret2);
-		else
+		} else {
+			io_async_list_note(READ, req, iov_count);
 			ret = -EAGAIN;
+		}
 	}
 	kfree(iovec);
 out_fput:
@@ -824,6 +880,7 @@ static ssize_t io_write(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	struct kiocb *kiocb = &req->rw;
 	struct iov_iter iter;
 	struct file *file;
+	size_t iov_count;
 	ssize_t ret;
 
 	ret = io_prep_rw(req, sqe, force_nonblock, state);
@@ -831,10 +888,6 @@ static ssize_t io_write(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 		return ret;
 	file = kiocb->ki_filp;
 
-	ret = -EAGAIN;
-	if (force_nonblock && !(kiocb->ki_flags & IOCB_DIRECT))
-		goto out_fput;
-
 	ret = -EBADF;
 	if (unlikely(!(file->f_mode & FMODE_WRITE)))
 		goto out_fput;
@@ -846,8 +899,15 @@ static ssize_t io_write(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	if (ret)
 		goto out_fput;
 
-	ret = rw_verify_area(WRITE, file, &kiocb->ki_pos,
-				iov_iter_count(&iter));
+	iov_count = iov_iter_count(&iter);
+
+	ret = -EAGAIN;
+	if (force_nonblock && !(kiocb->ki_flags & IOCB_DIRECT)) {
+		io_async_list_note(WRITE, req, iov_count);
+		goto out_free;
+	}
+
+	ret = rw_verify_area(WRITE, file, &kiocb->ki_pos, iov_count);
 	if (!ret) {
 		/*
 		 * Open-code file_start_write here to grab freeze protection,
@@ -865,6 +925,7 @@ static ssize_t io_write(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 		kiocb->ki_flags |= IOCB_WRITE;
 		io_rw_done(kiocb, call_write_iter(file, kiocb, &iter));
 	}
+out_free:
 	kfree(iovec);
 out_fput:
 	if (unlikely(ret))
@@ -1212,6 +1273,21 @@ static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 	return 0;
 }
 
+static struct async_list *io_async_list_from_sqe(struct io_ring_ctx *ctx,
+						 const struct io_uring_sqe *sqe)
+{
+	switch (sqe->opcode) {
+	case IORING_OP_READV:
+	case IORING_OP_READ_FIXED:
+		return &ctx->pending_async[READ];
+	case IORING_OP_WRITEV:
+	case IORING_OP_WRITE_FIXED:
+		return &ctx->pending_async[WRITE];
+	default:
+		return NULL;
+	}
+}
+
 static inline bool io_sqe_needs_user(const struct io_uring_sqe *sqe)
 {
 	return !(sqe->opcode == IORING_OP_READ_FIXED ||
@@ -1221,50 +1297,124 @@ static inline bool io_sqe_needs_user(const struct io_uring_sqe *sqe)
 static void io_sq_wq_submit_work(struct work_struct *work)
 {
 	struct io_kiocb *req = container_of(work, struct io_kiocb, work);
-	struct sqe_submit *s = &req->submit;
-	u64 user_data = s->sqe->user_data;
 	struct io_ring_ctx *ctx = req->ctx;
+	struct mm_struct *cur_mm = NULL;
 	struct files_struct *old_files;
+	struct async_list *async_list;
+	LIST_HEAD(req_list);
 	mm_segment_t old_fs;
-	bool needs_user;
 	int ret;
 
-	 /* Ensure we clear previously set forced non-block flag */
-	req->flags &= ~REQ_F_FORCE_NONBLOCK;
-
 	old_files = current->files;
 	current->files = ctx->sqo_files;
 
+	async_list = io_async_list_from_sqe(ctx, req->submit.sqe);
+restart:
+	do {
+		struct sqe_submit *s = &req->submit;
+		u64 user_data = s->sqe->user_data;
+
+		/* Ensure we clear previously set forced non-block flag */
+		req->flags &= ~REQ_F_FORCE_NONBLOCK;
+
+		ret = 0;
+		if (io_sqe_needs_user(s->sqe) && !cur_mm) {
+			if (!mmget_not_zero(ctx->sqo_mm)) {
+				ret = -EFAULT;
+			} else {
+				cur_mm = ctx->sqo_mm;;
+				use_mm(ctx->sqo_mm);
+				old_fs = get_fs();
+				set_fs(USER_DS);
+			}
+		}
+
+		if (!ret)
+			ret = __io_submit_sqe(ctx, req, s, false, NULL);
+		if (ret) {
+			io_cqring_add_event(ctx, user_data, ret, 0);
+			io_free_req(req);
+		}
+		if (!async_list)
+			break;
+		if (!list_empty(&req_list)) {
+			req = list_first_entry(&req_list, struct io_kiocb,
+						list);
+			list_del(&req->list);
+			continue;
+		}
+		if (list_empty(&async_list->list))
+			break;
+
+		req = NULL;
+		spin_lock(&async_list->lock);
+		if (list_empty(&async_list->list)) {
+			spin_unlock(&async_list->lock);
+			break;
+		}
+		list_splice_init(&async_list->list, &req_list);
+		spin_unlock(&async_list->lock);
+
+		req = list_first_entry(&req_list, struct io_kiocb, list);
+		list_del(&req->list);
+	} while (req);
+
 	/*
-	 * If we're doing IO to fixed buffers, we don't need to get/set
-	 * user context
+	 * Rare case of racing with a submitter. If we find the count has
+	 * dropped to zero AND we have pending work items, then restart
+	 * the processing. This is a tiny race window.
 	 */
-	needs_user = io_sqe_needs_user(s->sqe);
-	if (needs_user) {
-		if (!mmget_not_zero(ctx->sqo_mm)) {
-			ret = -EFAULT;
-			goto err;
+	ret = atomic_dec_return(&async_list->cnt);
+	while (!ret && !list_empty(&async_list->list)) {
+		spin_lock(&async_list->lock);
+		atomic_inc(&async_list->cnt);
+		list_splice_init(&async_list->list, &req_list);
+		spin_unlock(&async_list->lock);
+
+		if (!list_empty(&req_list)) {
+			req = list_first_entry(&req_list, struct io_kiocb,
+						list);
+			list_del(&req->list);
+			goto restart;
 		}
-		use_mm(ctx->sqo_mm);
-		old_fs = get_fs();
-		set_fs(USER_DS);
+		ret = atomic_dec_return(&async_list->cnt);
 	}
 
-	ret = __io_submit_sqe(ctx, req, s, false, NULL);
-
-	if (needs_user) {
+	if (cur_mm) {
 		set_fs(old_fs);
-		unuse_mm(ctx->sqo_mm);
-		mmput(ctx->sqo_mm);
-	}
-err:
-	if (ret) {
-		io_cqring_add_event(ctx, user_data, ret, 0);
-		io_free_req(req);
+		unuse_mm(cur_mm);
+		mmput(cur_mm);
 	}
 	current->files = old_files;
 }
 
+/*
+ * See if we can piggy back onto previously submitted work, that is still
+ * running. We currently only allow this if the new request is sequential
+ * to the previous one we punted.
+ */
+static bool io_add_to_prev_work(struct async_list *list, struct io_kiocb *req)
+{
+	bool ret = false;
+
+	if (!list)
+		return false;
+	if (!(req->flags & REQ_F_SEQ_PREV))
+		return false;
+	if (!atomic_read(&list->cnt))
+		return false;
+
+	ret = true;
+	spin_lock(&list->lock);
+	list_add_tail(&req->list, &list->list);
+	if (!atomic_read(&list->cnt)) {
+		list_del_init(&req->list);
+		ret = false;
+	}
+	spin_unlock(&list->lock);
+	return ret;
+}
+
 static int io_submit_sqe(struct io_ring_ctx *ctx, struct sqe_submit *s,
 			 struct io_submit_state *state)
 {
@@ -1281,9 +1431,16 @@ static int io_submit_sqe(struct io_ring_ctx *ctx, struct sqe_submit *s,
 
 	ret = __io_submit_sqe(ctx, req, s, true, state);
 	if (ret == -EAGAIN) {
+		struct async_list *list;
+
+		list = io_async_list_from_sqe(ctx, s->sqe);
 		memcpy(&req->submit, s, sizeof(*s));
-		INIT_WORK(&req->work, io_sq_wq_submit_work);
-		queue_work(ctx->sqo_wq, &req->work);
+		if (!io_add_to_prev_work(list, req)) {
+			if (list)
+				atomic_inc(&list->cnt);
+			INIT_WORK(&req->work, io_sq_wq_submit_work);
+			queue_work(ctx->sqo_wq, &req->work);
+		}
 		ret = 0;
 	}
 	if (ret)
-- 
2.17.1

[PATCH 18/18] io_uring: add io_uring_event cache hit information

[Jens Axboe]

Add hint on whether a read was served out of the page cache, or if it
hit media. This is useful for buffered async IO, O_DIRECT reads would
never have this set (for obvious reasons).

If the read hit page cache, cqe->flags will have IOCQE_FLAG_CACHEHIT
set.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c                 | 7 ++++++-
 include/uapi/linux/io_uring.h | 5 +++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index aa903fa902d5..a40b1af356e0 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -561,11 +561,16 @@ static void io_fput(struct io_kiocb *req)
 static void io_complete_rw(struct kiocb *kiocb, long res, long res2)
 {
 	struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw);
+	unsigned ev_flags = 0;
 
 	kiocb_end_write(kiocb);
 
 	io_fput(req);
-	io_cqring_add_event(req->ctx, req->user_data, res, 0);
+
+	if (res > 0 && (req->flags & REQ_F_FORCE_NONBLOCK))
+		ev_flags = IOCQE_FLAG_CACHEHIT;
+
+	io_cqring_add_event(req->ctx, req->user_data, res, ev_flags);
 	io_free_req(req);
 }
 
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 60b52c551c87..3b8d623031ad 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -71,6 +71,11 @@ struct io_uring_cqe {
 	__u32	flags;
 };
 
+/*
+ * io_uring_event->flags
+ */
+#define IOCQE_FLAG_CACHEHIT	(1 << 0)	/* IO did not hit media */
+
 /*
  * Magic offsets for the application to mmap the data it needs
  */
-- 
2.17.1

Re: [PATCH 05/18] Add io_uring IO interface

[Jann Horn]

On Fri, Feb 1, 2019 at 6:04 PM Jann Horn <jannh@google.com> wrote:
>
> On Fri, Feb 1, 2019 at 5:57 PM Matt Mullins <mmullins@fb.com> wrote:
> > On Tue, 2019-01-29 at 00:59 +0100, Jann Horn wrote:
> > > On Tue, Jan 29, 2019 at 12:47 AM Jens Axboe <axboe@kernel.dk> wrote:
> > > > On 1/28/19 3:32 PM, Jann Horn wrote:
> > > > > On Mon, Jan 28, 2019 at 10:35 PM Jens Axboe <axboe@kernel.dk> wrote:
> > > > > > The submission queue (SQ) and completion queue (CQ) rings are shared
> > > > > > between the application and the kernel. This eliminates the need to
> > > > > > copy data back and forth to submit and complete IO.
> > > > > >
> > > > > > IO submissions use the io_uring_sqe data structure, and completions
> > > > > > are generated in the form of io_uring_sqe data structures. The SQ
> > > > > > ring is an index into the io_uring_sqe array, which makes it possible
> > > > > > to submit a batch of IOs without them being contiguous in the ring.
> > > > > > The CQ ring is always contiguous, as completion events are inherently
> > > > > > unordered, and hence any io_uring_cqe entry can point back to an
> > > > > > arbitrary submission.
> > > > > >
> > > > > > Two new system calls are added for this:
> > > > > >
> > > > > > io_uring_setup(entries, params)
> > > > > >         Sets up a context for doing async IO. On success, returns a file
> > > > > >         descriptor that the application can mmap to gain access to the
> > > > > >         SQ ring, CQ ring, and io_uring_sqes.
> > > > > >
> > > > > > io_uring_enter(fd, to_submit, min_complete, flags, sigset, sigsetsize)
> > > > > >         Initiates IO against the rings mapped to this fd, or waits for
> > > > > >         them to complete, or both. The behavior is controlled by the
> > > > > >         parameters passed in. If 'to_submit' is non-zero, then we'll
> > > > > >         try and submit new IO. If IORING_ENTER_GETEVENTS is set, the
> > > > > >         kernel will wait for 'min_complete' events, if they aren't
> > > > > >         already available. It's valid to set IORING_ENTER_GETEVENTS
> > > > > >         and 'min_complete' == 0 at the same time, this allows the
> > > > > >         kernel to return already completed events without waiting
> > > > > >         for them. This is useful only for polling, as for IRQ
> > > > > >         driven IO, the application can just check the CQ ring
> > > > > >         without entering the kernel.
> > > > > >
> > > > > > With this setup, it's possible to do async IO with a single system
> > > > > > call. Future developments will enable polled IO with this interface,
> > > > > > and polled submission as well. The latter will enable an application
> > > > > > to do IO without doing ANY system calls at all.
> > > > > >
> > > > > > For IRQ driven IO, an application only needs to enter the kernel for
> > > > > > completions if it wants to wait for them to occur.
> > > > > >
> > > > > > Each io_uring is backed by a workqueue, to support buffered async IO
> > > > > > as well. We will only punt to an async context if the command would
> > > > > > need to wait for IO on the device side. Any data that can be accessed
> > > > > > directly in the page cache is done inline. This avoids the slowness
> > > > > > issue of usual threadpools, since cached data is accessed as quickly
> > > > > > as a sync interface.
> > > > > >
> > > > > > Sample application: https://urldefense.proofpoint.com/v2/url?u=http-3A__git.kernel.dk_cgit_fio_plain_t_io-5Furing.c&d=DwIBaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=pqM-eO4A2hNFhIFiX-7eGg&m=MGr14pOzNbC7Z-8_dV4GMiH3AbkkH0RSQoQ894Tu0yc&s=mgbcubzOMiCpFpnwW-HA3ey0YDYPkgMIZ7Bmy4w6Chc&e=
> > > > >
> > > > > [...]
> > > > > > +static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
> > > > > > +                     bool force_nonblock)
> > > > > > +{
> > > > > > +       struct kiocb *kiocb = &req->rw;
> > > > > > +       int ret;
> > > > > > +
> > > > > > +       kiocb->ki_filp = fget(sqe->fd);
> > > > > > +       if (unlikely(!kiocb->ki_filp))
> > > > > > +               return -EBADF;
> > > > > > +       kiocb->ki_pos = sqe->off;
> > > > > > +       kiocb->ki_flags = iocb_flags(kiocb->ki_filp);
> > > > > > +       kiocb->ki_hint = ki_hint_validate(file_write_hint(kiocb->ki_filp));
> > > > > > +       if (sqe->ioprio) {
> > > > > > +               ret = ioprio_check_cap(sqe->ioprio);
> > > > > > +               if (ret)
> > > > > > +                       goto out_fput;
> > > > > > +
> > > > > > +               kiocb->ki_ioprio = sqe->ioprio;
> > > > > > +       } else
> > > > > > +               kiocb->ki_ioprio = get_current_ioprio();
> > > > > > +
> > > > > > +       ret = kiocb_set_rw_flags(kiocb, sqe->rw_flags);
> > > > > > +       if (unlikely(ret))
> > > > > > +               goto out_fput;
> > > > > > +       if (force_nonblock) {
> > > > > > +               kiocb->ki_flags |= IOCB_NOWAIT;
> > > > > > +               req->flags |= REQ_F_FORCE_NONBLOCK;
> > > > > > +       }
> > > > > > +       if (kiocb->ki_flags & IOCB_HIPRI) {
> > > > > > +               ret = -EINVAL;
> > > > > > +               goto out_fput;
> > > > > > +       }
> > > > > > +
> > > > > > +       kiocb->ki_complete = io_complete_rw;
> > > > > > +       return 0;
> > > > > > +out_fput:
> > > > > > +       fput(kiocb->ki_filp);
> > > > > > +       return ret;
> > > > > > +}
> > > > >
> > > > > [...]
> > > > > > +static ssize_t io_read(struct io_kiocb *req, const struct io_uring_sqe *sqe,
> > > > > > +                      bool force_nonblock)
> > > > > > +{
> > > > > > +       struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
> > > > > > +       struct kiocb *kiocb = &req->rw;
> > > > > > +       struct iov_iter iter;
> > > > > > +       struct file *file;
> > > > > > +       ssize_t ret;
> > > > > > +
> > > > > > +       ret = io_prep_rw(req, sqe, force_nonblock);
> > > > > > +       if (ret)
> > > > > > +               return ret;
> > > > > > +       file = kiocb->ki_filp;
> > > > > > +
> > > > > > +       ret = -EBADF;
> > > > > > +       if (unlikely(!(file->f_mode & FMODE_READ)))
> > > > > > +               goto out_fput;
> > > > > > +       ret = -EINVAL;
> > > > > > +       if (unlikely(!file->f_op->read_iter))
> > > > > > +               goto out_fput;
> > > > > > +
> > > > > > +       ret = io_import_iovec(req->ctx, READ, sqe, &iovec, &iter);
> > > > > > +       if (ret)
> > > > > > +               goto out_fput;
> > > > > > +
> > > > > > +       ret = rw_verify_area(READ, file, &kiocb->ki_pos, iov_iter_count(&iter));
> > > > > > +       if (!ret) {
> > > > > > +               ssize_t ret2;
> > > > > > +
> > > > > > +               /* Catch -EAGAIN return for forced non-blocking submission */
> > > > > > +               ret2 = call_read_iter(file, kiocb, &iter);
> > > > > > +               if (!force_nonblock || ret2 != -EAGAIN)
> > > > > > +                       io_rw_done(kiocb, ret2);
> > > > > > +               else
> > > > > > +                       ret = -EAGAIN;
> > > > > > +       }
> > > > > > +       kfree(iovec);
> > > > > > +out_fput:
> > > > > > +       if (unlikely(ret))
> > > > > > +               fput(file);
> > > > > > +       return ret;
> > > > > > +}
> > > > >
> > > > > [...]
> > > > > > +static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
> > > > > > +                          struct sqe_submit *s, bool force_nonblock)
> > > > > > +{
> > > > > > +       const struct io_uring_sqe *sqe = s->sqe;
> > > > > > +       ssize_t ret;
> > > > > > +
> > > > > > +       if (unlikely(s->index >= ctx->sq_entries))
> > > > > > +               return -EINVAL;
> > > > > > +       req->user_data = sqe->user_data;
> > > > > > +
> > > > > > +       ret = -EINVAL;
> > > > > > +       switch (sqe->opcode) {
> > > > > > +       case IORING_OP_NOP:
> > > > > > +               ret = io_nop(req, sqe);
> > > > > > +               break;
> > > > > > +       case IORING_OP_READV:
> > > > > > +               ret = io_read(req, sqe, force_nonblock);
> > > > > > +               break;
> > > > > > +       case IORING_OP_WRITEV:
> > > > > > +               ret = io_write(req, sqe, force_nonblock);
> > > > > > +               break;
> > > > > > +       default:
> > > > > > +               ret = -EINVAL;
> > > > > > +               break;
> > > > > > +       }
> > > > > > +
> > > > > > +       return ret;
> > > > > > +}
> > > > > > +
> > > > > > +static void io_sq_wq_submit_work(struct work_struct *work)
> > > > > > +{
> > > > > > +       struct io_kiocb *req = container_of(work, struct io_kiocb, work);
> > > > > > +       struct sqe_submit *s = &req->submit;
> > > > > > +       u64 user_data = s->sqe->user_data;
> > > > > > +       struct io_ring_ctx *ctx = req->ctx;
> > > > > > +       mm_segment_t old_fs = get_fs();
> > > > > > +       struct files_struct *old_files;
> > > > > > +       int ret;
> > > > > > +
> > > > > > +        /* Ensure we clear previously set forced non-block flag */
> > > > > > +       req->flags &= ~REQ_F_FORCE_NONBLOCK;
> > > > > > +
> > > > > > +       old_files = current->files;
> > > > > > +       current->files = ctx->sqo_files;
> > > > >
> > > > > I think you're not supposed to twiddle with current->files without
> > > > > holding task_lock(current).
> > > >
> > > > 'current' is the work queue item in this case, do we need to protect
> > > > against anything else? I can add the locking around the assignments
> > > > (both places).
> > >
> > > Stuff like proc_fd_link() uses get_files_struct(), which grabs a
> > > reference to your current files_struct protected only by task_lock();
> > > and it doesn't use anything like READ_ONCE(), so even if the object
> > > lifetime is not a problem, get_files_struct() could potentially crash
> > > due to a double-read (reading task->files twice and assuming that the
> > > result will be the same). As far as I can tell, this procfs code also
> > > works on kernel threads.
> > >
> > > > > > +       if (!mmget_not_zero(ctx->sqo_mm)) {
> > > > > > +               ret = -EFAULT;
> > > > > > +               goto err;
> > > > > > +       }
> > > > > > +
> > > > > > +       use_mm(ctx->sqo_mm);
> > > > > > +       set_fs(USER_DS);
> > > > > > +
> > > > > > +       ret = __io_submit_sqe(ctx, req, s, false);
> > > > > > +
> > > > > > +       set_fs(old_fs);
> > > > > > +       unuse_mm(ctx->sqo_mm);
> > > > > > +       mmput(ctx->sqo_mm);
> > > > > > +err:
> > > > > > +       if (ret) {
> > > > > > +               io_cqring_add_event(ctx, user_data, ret, 0);
> > > > > > +               io_free_req(req);
> > > > > > +       }
> > > > > > +       current->files = old_files;
> > > > > > +}
> > > > >
> > > > > [...]
> > > > > > +static int io_sq_offload_start(struct io_ring_ctx *ctx)
> > > > > > +{
> > > > > > +       int ret;
> > > > > > +
> > > > > > +       ctx->sqo_mm = current->mm;
> > > > >
> > > > > What keeps this thing alive?
> > > >
> > > > I think we're deadling with the same thing as the files below, I'll
> > > > defer to that.
> > > >
> > > > > > +       /*
> > > > > > +        * This is safe since 'current' has the fd installed, and if that gets
> > > > > > +        * closed on exit, then fops->release() is invoked which waits for the
> > > > > > +        * async contexts to flush and exit before exiting.
> > > > > > +        */
> > > > > > +       ret = -EBADF;
> > > > > > +       ctx->sqo_files = current->files;
> > > > > > +       if (!ctx->sqo_files)
> > > > > > +               goto err;
> > > > >
> > > > > That's gnarly. Adding Al Viro to the thread.
> > > > >
> > > > > I think you misunderstand the semantics of f_op->release. The ->flush
> > > > > handler is invoked whenever a file descriptor is closed through
> > > > > filp_close() (via deletion of the files_struct, sys_close(),
> > > > > sys_dup2(), ...), so if you had used that one, _maybe_ this would
> > > > > work. But the ->release handler only runs when the _last_ reference to
> > > > > a struct file has been dropped - so you can, for example, fork() a
> > > > > child, then exit() in the parent, and the ->release handler isn't
> > > > > invoked. So I don't see how this can work.
> > > >
> > > > The anonfd is CLOEXEC. The idea is exactly that it only runs when the
> > > > last reference to the file has been dropped. Not sure why you think I
> > > > need ->flush() here?
> > >
> > > Can't I just use fcntl(fd, F_SETFD, fd, 0) to clear the CLOEXEC flag?
> > > Or send the fd via SCM_RIGHTS?
> > >
> > > > > But even if you had abused ->flush for this instead: close_files()
> > > > > currently has a comment in it that claims that "this is the last
> > > > > reference to the files structure"; this change would make that claim
> > > > > untrue.
> > > >
> > > > Let me see if I can explain my intent better than that comment... We
> > > > know the parent who set up the io_uring instance will be around for as
> > > > long as io_uring instance persists.
> > >
> > > That's the part that I think is wrong: As far as I can tell, the
> > > parent can go away and you won't notice.
> > >
> > > Also, note that "the parent" is different things for ->files and ->mm.
> > > You can have a multithreaded process whose threads don't have the same
> > > ->files, or multiple process that share ->files without sharing ->mm,
> > > ...
> >
> > This had actually been get_files_struct() in early versions, and I had
> > reported to Jens that it allows something like
> >
> > int main() {
> >   struct io_uring_params uring_params = {
> >         .flags = IORING_SETUP_SQPOLL,
> >   };
> >   int uring_fd = syscall(425 /* io_uring_setup */, 16, &uring_params);
> > }
> >
> > to leak both the files_struct and the kthread, as the files_struct and
> > the uring context form a circular reference.  I haven't really come up
> > with a good way to reconcile the requirements here; perhaps we need an
> > exit_uring() akin to exit_aio()?
>
> Oh, yuck. Uuuh... can we make "struct files_struct" doubly-refcounted,
> like "struct mm_struct"? One reference type to keep the contents
> intact (the reference type you normally use, and the type used by
> uring when the thread is running), and one reference type to just keep
> the struct itself existing, but without preserving its contents
> (reference held consistently by the uring thread)?

Something like this (completely untested); and then instead of the
current get_files_struct(), you'd do get_files_struct_weak(), and
while the thread is running, it protects the files_struct from dying
with tryget_weak_files_struct() / put_files_struct().

Al, do you have opinions on this?

===============
diff --git a/fs/file.c b/fs/file.c
index 3209ee271c41..fbf02ef2753d 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -281,6 +281,7 @@ struct files_struct *dup_fd(struct files_struct
*oldf, int *errorp)
        if (!newf)
                goto out;

+       kref_init(&newf->weak_refs);
        atomic_set(&newf->count, 1);

        spin_lock_init(&newf->file_lock);
@@ -410,6 +411,26 @@ struct files_struct *get_files_struct(struct
task_struct *task)
        return files;
 }

+static void free_files_struct(struct kref *ref) {
+       struct files_struct *files =
+               container_of(ref, struct files_struct, weak_refs);
+       kmem_cache_free(files_cachep, files);
+}
+
+void put_files_struct_weak(struct files_struct *files) {
+       kref_put(&files->weak_refs, free_files_struct);
+}
+
+struct files_struct *get_files_struct_weak(struct task_struct *task)
+{
+       struct files_struct *files = get_files_struct(task);
+       if (files) {
+               kref_get(&files->weak_refs);
+               put_files_struct(files);
+       }
+       return files;
+}
+
 void put_files_struct(struct files_struct *files)
 {
        if (atomic_dec_and_test(&files->count)) {
@@ -418,10 +439,17 @@ void put_files_struct(struct files_struct *files)
                /* free the arrays if they are not embedded */
                if (fdt != &files->fdtab)
                        __free_fdtable(fdt);
-               kmem_cache_free(files_cachep, files);
+               put_files_struct_weak(files);
        }
 }

+struct files_struct *tryget_weak_files_struct(struct files_struct *fs) {
+       if (atomic_inc_not_zero(&fs->count)) {
+               return fs;
+       }
+       return NULL;
+}
+
 void reset_files_struct(struct files_struct *files)
 {
        struct task_struct *tsk = current;
@@ -448,6 +476,7 @@ void exit_files(struct task_struct *tsk)

 struct files_struct init_files = {
        .count          = ATOMIC_INIT(1),
+       .weak_refs      = KREF_INIT(1),
        .fdt            = &init_files.fdtab,
        .fdtab          = {
                .max_fds        = NR_OPEN_DEFAULT,
diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
index f07c55ea0c22..6ad95a95cc0b 100644
--- a/include/linux/fdtable.h
+++ b/include/linux/fdtable.h
@@ -14,6 +14,7 @@
 #include <linux/types.h>
 #include <linux/init.h>
 #include <linux/fs.h>
+#include <linux/kref.h>

 #include <linux/atomic.h>

@@ -50,6 +51,7 @@ struct files_struct {
    * read mostly part
    */
        atomic_t count;
+       struct kref weak_refs;
        bool resize_in_progress;
        wait_queue_head_t resize_wait;

@@ -107,6 +109,9 @@ struct task_struct;

 struct files_struct *get_files_struct(struct task_struct *);
 void put_files_struct(struct files_struct *fs);
+void put_files_struct_weak(struct files_struct *files);
+struct files_struct *get_files_struct_weak(struct task_struct *);
+struct files_struct *tryget_weak_files_struct(struct files_struct *);
 void reset_files_struct(struct files_struct *);
 int unshare_files(struct files_struct **);
 struct files_struct *dup_fd(struct files_struct *, int *) __latent_entropy;
===============

Re: [PATCH 05/18] Add io_uring IO interface

[Al Viro]

On Fri, Feb 01, 2019 at 06:23:27PM +0100, Jann Horn wrote:

> > Oh, yuck. Uuuh... can we make "struct files_struct" doubly-refcounted,
> > like "struct mm_struct"? One reference type to keep the contents
> > intact (the reference type you normally use, and the type used by
> > uring when the thread is running), and one reference type to just keep
> > the struct itself existing, but without preserving its contents
> > (reference held consistently by the uring thread)?
> 
> Something like this (completely untested); and then instead of the
> current get_files_struct(), you'd do get_files_struct_weak(), and
> while the thread is running, it protects the files_struct from dying
> with tryget_weak_files_struct() / put_files_struct().
> 
> Al, do you have opinions on this?

Yes, but they are not fit for polite company.  IMO the entire approach
is FUBAR; I'll post more detailed review, but what I'd seen so far is
a veto fodder.