[PATCH v2] io_uring: let IORING_OP_FILES_UPDATE support to choose fixed file slots

[Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>]

One big issue with file registration feature is that it needs user
space apps to maintain free slot info about io_uring's fixed file
table, which really is a burden for development. Now since io_uring
starts to choose free file slot for user space apps by using
IORING_FILE_INDEX_ALLOC flag in accept or open operations, but they
need app to uses direct accept or direct open, which as far as I know,
some apps are not prepared to use direct accept or open yet.

To support apps, who still need real fds, use registration feature
easier, let IORING_OP_FILES_UPDATE support to choose fixed file slots,
which will store picked fixed files slots in fd array and let cqe return
the number of slots allocated.

Suggested-by: Hao Xu <howeyxu@tencent.com>
Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
---
V2:
  Add illegal flags check in io_close_prep().
---
 fs/io_uring.c                 | 75 +++++++++++++++++++++++++++++++++++++------
 include/uapi/linux/io_uring.h |  1 +
 2 files changed, 66 insertions(+), 10 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 6d91148e9679..18a7459fb6e7 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -574,6 +574,7 @@ struct io_close {
 	struct file			*file;
 	int				fd;
 	u32				file_slot;
+	u32				flags;
 };
 
 struct io_timeout_data {
@@ -1366,7 +1367,9 @@ static int io_req_prep_async(struct io_kiocb *req);
 
 static int io_install_fixed_file(struct io_kiocb *req, struct file *file,
 				 unsigned int issue_flags, u32 slot_index);
-static int io_close_fixed(struct io_kiocb *req, unsigned int issue_flags);
+static int __io_close_fixed(struct io_kiocb *req, unsigned int issue_flags,
+			    unsigned int offset);
+static inline int io_close_fixed(struct io_kiocb *req, unsigned int issue_flags);
 
 static enum hrtimer_restart io_link_timeout_fn(struct hrtimer *timer);
 static void io_eventfd_signal(struct io_ring_ctx *ctx);
@@ -5945,16 +5948,22 @@ static int io_statx(struct io_kiocb *req, unsigned int issue_flags)
 	return 0;
 }
 
+#define IORING_CLOSE_FD_AND_FILE_SLOT 1
+
 static int io_close_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 {
-	if (sqe->off || sqe->addr || sqe->len || sqe->rw_flags || sqe->buf_index)
+	if (sqe->off || sqe->addr || sqe->len || sqe->buf_index)
 		return -EINVAL;
 	if (req->flags & REQ_F_FIXED_FILE)
 		return -EBADF;
 
 	req->close.fd = READ_ONCE(sqe->fd);
 	req->close.file_slot = READ_ONCE(sqe->file_index);
-	if (req->close.file_slot && req->close.fd)
+	req->close.flags = READ_ONCE(sqe->close_flags);
+	if (req->close.flags & ~IORING_CLOSE_FD_AND_FILE_SLOT)
+		return -EINVAL;
+	if (!(req->close.flags & IORING_CLOSE_FD_AND_FILE_SLOT) &&
+	    req->close.file_slot && req->close.fd)
 		return -EINVAL;
 
 	return 0;
@@ -5970,7 +5979,8 @@ static int io_close(struct io_kiocb *req, unsigned int issue_flags)
 
 	if (req->close.file_slot) {
 		ret = io_close_fixed(req, issue_flags);
-		goto err;
+		if (ret || !(req->close.flags & IORING_CLOSE_FD_AND_FILE_SLOT))
+			goto err;
 	}
 
 	spin_lock(&files->file_lock);
@@ -8003,6 +8013,42 @@ static int io_files_update_prep(struct io_kiocb *req,
 	return 0;
 }
 
+static int io_files_update_with_index_alloc(struct io_kiocb *req,
+					    unsigned int issue_flags)
+{
+	__s32 __user *fds = u64_to_user_ptr(req->rsrc_update.arg);
+	struct file *file;
+	unsigned int done, nr_fds = req->rsrc_update.nr_args;
+	int ret, fd;
+
+	for (done = 0; done < nr_fds; done++) {
+		if (copy_from_user(&fd, &fds[done], sizeof(fd))) {
+			ret = -EFAULT;
+			break;
+		}
+
+		file = fget(fd);
+		if (!file) {
+			ret = -EBADF;
+			goto out;
+		}
+		ret = io_fixed_fd_install(req, issue_flags, file,
+					  IORING_FILE_INDEX_ALLOC);
+		if (ret < 0)
+			goto out;
+		if (copy_to_user(&fds[done], &ret, sizeof(ret))) {
+			ret = -EFAULT;
+			__io_close_fixed(req, issue_flags, ret);
+			break;
+		}
+	}
+
+out:
+	if (done)
+		return done;
+	return ret;
+}
+
 static int io_files_update(struct io_kiocb *req, unsigned int issue_flags)
 {
 	struct io_ring_ctx *ctx = req->ctx;
@@ -8016,10 +8062,14 @@ static int io_files_update(struct io_kiocb *req, unsigned int issue_flags)
 	up.resv = 0;
 	up.resv2 = 0;
 
-	io_ring_submit_lock(ctx, issue_flags);
-	ret = __io_register_rsrc_update(ctx, IORING_RSRC_FILE,
-					&up, req->rsrc_update.nr_args);
-	io_ring_submit_unlock(ctx, issue_flags);
+	if (req->rsrc_update.offset == IORING_FILE_INDEX_ALLOC) {
+		ret = io_files_update_with_index_alloc(req, issue_flags);
+	} else {
+		io_ring_submit_lock(ctx, issue_flags);
+		ret = __io_register_rsrc_update(ctx, IORING_RSRC_FILE,
+				&up, req->rsrc_update.nr_args);
+		io_ring_submit_unlock(ctx, issue_flags);
+	}
 
 	if (ret < 0)
 		req_set_fail(req);
@@ -10183,9 +10233,9 @@ static int io_install_fixed_file(struct io_kiocb *req, struct file *file,
 	return ret;
 }
 
-static int io_close_fixed(struct io_kiocb *req, unsigned int issue_flags)
+static int __io_close_fixed(struct io_kiocb *req, unsigned int issue_flags,
+			    unsigned int offset)
 {
-	unsigned int offset = req->close.file_slot - 1;
 	struct io_ring_ctx *ctx = req->ctx;
 	struct io_fixed_file *file_slot;
 	struct file *file;
@@ -10222,6 +10272,11 @@ static int io_close_fixed(struct io_kiocb *req, unsigned int issue_flags)
 	return ret;
 }
 
+static inline int io_close_fixed(struct io_kiocb *req, unsigned int issue_flags)
+{
+	return __io_close_fixed(req, issue_flags, req->close.file_slot - 1);
+}
+
 static int __io_sqe_files_update(struct io_ring_ctx *ctx,
 				 struct io_uring_rsrc_update2 *up,
 				 unsigned nr_args)
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 53e7dae92e42..e347b3fea4e4 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -47,6 +47,7 @@ struct io_uring_sqe {
 		__u32		unlink_flags;
 		__u32		hardlink_flags;
 		__u32		xattr_flags;
+		__u32		close_flags;
 	};
 	__u64	user_data;	/* data to be passed back at completion time */
 	/* pack this to avoid bogus arm OABI complaints */
-- 
2.14.4.44.g2045bb6