[PATCH 2/8] nowait aio: Introduce RWF_NOWAIT

[Goldwyn Rodrigues <rgoldwyn@suse.de>]

From: Goldwyn Rodrigues <rgoldwyn@suse.com>

This flag informs kernel to bail out if an AIO request will block
for reasons such as file allocations, or a writeback triggered,
or would block while allocating requests while performing
direct I/O.

Unfortunately, aio_flags is not checked for validity, which would
break existing applications which have it set to anything besides zero
or IOCB_FLAG_RESFD. So, we are using aio_reserved1 and renaming it
to aio_rw_flags.

RWF_NOWAIT is translated to IOCB_NOWAIT for iocb->ki_flags.

The check for -EOPNOTSUPP is placed in generic_file_write_iter(). This
is called by most filesystems, either through fsops.write_iter() or through
the function defined by write_iter(). If not, we perform the check defined
by .write_iter() which is called for direct IO specifically.

Filesystems xfs, btrfs and ext4 would be supported in the following patches.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
---
 fs/9p/vfs_file.c        | 3 +++
 fs/aio.c                | 9 +++++++--
 fs/ceph/file.c          | 3 +++
 fs/cifs/file.c          | 3 +++
 fs/fuse/file.c          | 3 +++
 fs/nfs/direct.c         | 3 +++
 fs/ocfs2/file.c         | 3 +++
 fs/read_write.c         | 2 +-
 include/linux/fs.h      | 3 +++
 include/uapi/linux/fs.h | 1 +
 mm/filemap.c            | 3 +++
 11 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/fs/9p/vfs_file.c b/fs/9p/vfs_file.c
index 3de3b4a89d89..403681db7723 100644
--- a/fs/9p/vfs_file.c
+++ b/fs/9p/vfs_file.c
@@ -411,6 +411,9 @@ v9fs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	loff_t origin;
 	int err = 0;
 
+	if (iocb->ki_flags & IOCB_NOWAIT)
+		return -EOPNOTSUPP;
+
 	retval = generic_write_checks(iocb, from);
 	if (retval <= 0)
 		return retval;
diff --git a/fs/aio.c b/fs/aio.c
index b8a33f5beef5..d3b5c8dc6549 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1546,12 +1546,12 @@ static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
 		return -EINVAL;
 	}
 
-	if (unlikely(iocb->aio_rw_flags & ~(RWF_HIPRI | RWF_DSYNC | RWF_SYNC))) {
+	if (unlikely(iocb->aio_rw_flags &
+		     ~(RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT))) {
 		pr_debug("EINVAL: aio_rw_flags set with incompatible flags\n");
 		return -EINVAL;
 	}
 
-
 	/* prevent overflows */
 	if (unlikely(
 	    (iocb->aio_buf != (unsigned long)iocb->aio_buf) ||
@@ -1593,6 +1593,11 @@ static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
 	}
 
 	req->common.ki_flags |= iocb_rw_flags(iocb->aio_rw_flags);
+	if ((req->common.ki_flags & IOCB_NOWAIT) &&
+	    !(req->common.ki_flags & IOCB_DIRECT)) {
+			ret = -EINVAL;
+			goto out_put_req;
+		}
 
 	ret = put_user(KIOCB_KEY, &user_iocb->aio_key);
 	if (unlikely(ret)) {
diff --git a/fs/ceph/file.c b/fs/ceph/file.c
index 26cc95421cca..af28419b1731 100644
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -1267,6 +1267,9 @@ static ssize_t ceph_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	int err, want, got;
 	loff_t pos;
 
+	if (iocb->ki_flags & IOCB_NOWAIT)
+		return -EOPNOTSUPP;
+
 	if (ceph_snap(inode) != CEPH_NOSNAP)
 		return -EROFS;
 
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index aa3debbba826..a828ab3e7775 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -2638,6 +2638,9 @@ ssize_t cifs_user_writev(struct kiocb *iocb, struct iov_iter *from)
 	 * write request.
 	 */
 
+	if (iocb->ki_flags & IOCB_NOWAIT)
+		return -EOPNOTSUPP;
+
 	rc = generic_write_checks(iocb, from);
 	if (rc <= 0)
 		return rc;
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index ec238fb5a584..72786e798319 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1425,6 +1425,9 @@ static ssize_t fuse_direct_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(file);
 	ssize_t res;
 
+	if (iocb->ki_flags & IOCB_NOWAIT)
+		return -EOPNOTSUPP;
+
 	if (is_bad_inode(inode))
 		return -EIO;
 
diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c
index aab32fc3d6a8..ab419caebd5f 100644
--- a/fs/nfs/direct.c
+++ b/fs/nfs/direct.c
@@ -991,6 +991,9 @@ ssize_t nfs_file_direct_write(struct kiocb *iocb, struct iov_iter *iter)
 	dfprintk(FILE, "NFS: direct write(%pD2, %zd@%Ld)\n",
 		file, iov_iter_count(iter), (long long) iocb->ki_pos);
 
+	if (iocb->ki_flags & IOCB_NOWAIT)
+		return -EOPNOTSUPP;
+
 	result = generic_write_checks(iocb, iter);
 	if (result <= 0)
 		return result;
diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
index bfeb647459d9..e7f8ba890305 100644
--- a/fs/ocfs2/file.c
+++ b/fs/ocfs2/file.c
@@ -2235,6 +2235,9 @@ static ssize_t ocfs2_file_write_iter(struct kiocb *iocb,
 	if (count == 0)
 		return 0;
 
+	if (iocb->ki_flags & IOCB_NOWAIT)
+		return -EOPNOTSUPP;
+
 	direct_io = iocb->ki_flags & IOCB_DIRECT ? 1 : 0;
 
 	inode_lock(inode);
diff --git a/fs/read_write.c b/fs/read_write.c
index 9aa557bb471c..97f3d6d444b8 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -678,7 +678,7 @@ static ssize_t do_iter_readv_writev(struct file *filp, struct iov_iter *iter,
 	struct kiocb kiocb;
 	ssize_t ret;
 
-	if (flags & ~(RWF_HIPRI | RWF_DSYNC | RWF_SYNC))
+	if (flags & ~(RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT))
 		return -EOPNOTSUPP;
 
 	init_sync_kiocb(&kiocb, filp);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 35cfb08ceb9d..e44de1c981a0 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -270,6 +270,7 @@ struct writeback_control;
 #define IOCB_DSYNC		(1 << 4)
 #define IOCB_SYNC		(1 << 5)
 #define IOCB_WRITE		(1 << 6)
+#define IOCB_NOWAIT		(1 << 7)
 
 struct kiocb {
 	struct file		*ki_filp;
@@ -3058,6 +3059,8 @@ static inline int iocb_rw_flags(int flags)
 		res |= IOCB_DSYNC;
 	if (flags & RWF_SYNC)
 		res |= (IOCB_DSYNC | IOCB_SYNC);
+	if (flags & RWF_NOWAIT)
+		res |= IOCB_NOWAIT;
 	return res;
 }
 
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index 048a85e9f017..7bcaef101876 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -347,5 +347,6 @@ struct fscrypt_policy {
 #define RWF_HIPRI			0x00000001 /* high priority request, poll if possible */
 #define RWF_DSYNC			0x00000002 /* per-IO O_DSYNC */
 #define RWF_SYNC			0x00000004 /* per-IO O_SYNC */
+#define RWF_NOWAIT			0x00000008 /* per-IO, return -EAGAIN if operation would block */
 
 #endif /* _UAPI_LINUX_FS_H */
diff --git a/mm/filemap.c b/mm/filemap.c
index 1694623a6289..d51670b7fe6b 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2982,6 +2982,9 @@ ssize_t generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	struct inode *inode = file->f_mapping->host;
 	ssize_t ret;
 
+	if (iocb->ki_flags & IOCB_NOWAIT)
+		return -EOPNOTSUPP;
+
 	inode_lock(inode);
 	ret = generic_write_checks(iocb, from);
 	if (ret > 0)
-- 
2.12.0