[PATCH for-next 06/12] io_uring: add fixed file peeking function

[Dylan Yudaken <dylany@meta.com>]

Add a helper function to grab the fixed file at a given offset. Will be
useful for retarget op handlers.

Signed-off-by: Dylan Yudaken <dylany@meta.com>
---
 io_uring/io_uring.c | 26 ++++++++++++++++++++------
 io_uring/io_uring.h |  1 +
 2 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 32eb305c4ce7..a052653fc65e 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -1841,6 +1841,23 @@ void io_wq_submit_work(struct io_wq_work *work)
 		io_req_task_queue_fail(req, ret);
 }
 
+static unsigned long __io_file_peek_fixed(struct io_kiocb *req, int fd)
+	__must_hold(&req->ctx->uring_lock)
+{
+	struct io_ring_ctx *ctx = req->ctx;
+
+	if (unlikely((unsigned int)fd >= ctx->nr_user_files))
+		return 0;
+	fd = array_index_nospec(fd, ctx->nr_user_files);
+	return io_fixed_file_slot(&ctx->file_table, fd)->file_ptr;
+}
+
+struct file *io_file_peek_fixed(struct io_kiocb *req, int fd)
+	__must_hold(&req->ctx->uring_lock)
+{
+	return (struct file *) (__io_file_peek_fixed(req, fd) & FFS_MASK);
+}
+
 inline struct file *io_file_get_fixed(struct io_kiocb *req, int fd,
 				      unsigned int issue_flags)
 {
@@ -1849,17 +1866,14 @@ inline struct file *io_file_get_fixed(struct io_kiocb *req, int fd,
 	unsigned long file_ptr;
 
 	io_ring_submit_lock(ctx, issue_flags);
-
-	if (unlikely((unsigned int)fd >= ctx->nr_user_files))
-		goto out;
-	fd = array_index_nospec(fd, ctx->nr_user_files);
-	file_ptr = io_fixed_file_slot(&ctx->file_table, fd)->file_ptr;
+	file_ptr = __io_file_peek_fixed(req, fd);
 	file = (struct file *) (file_ptr & FFS_MASK);
 	file_ptr &= ~FFS_MASK;
 	/* mask in overlapping REQ_F and FFS bits */
 	req->flags |= (file_ptr << REQ_F_SUPPORT_NOWAIT_BIT);
 	io_req_set_rsrc_node(req, ctx, 0);
-out:
+	WARN_ON_ONCE(file && !test_bit(fd, ctx->file_table.bitmap));
+
 	io_ring_submit_unlock(ctx, issue_flags);
 	return file;
 }
diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
index ef77d2aa3172..781471bfba12 100644
--- a/io_uring/io_uring.h
+++ b/io_uring/io_uring.h
@@ -44,6 +44,7 @@ struct page **io_pin_pages(unsigned long ubuf, unsigned long len, int *npages);
 struct file *io_file_get_normal(struct io_kiocb *req, int fd);
 struct file *io_file_get_fixed(struct io_kiocb *req, int fd,
 			       unsigned issue_flags);
+struct file *io_file_peek_fixed(struct io_kiocb *req, int fd);
 
 static inline bool io_req_ffs_set(struct io_kiocb *req)
 {
-- 
2.30.2