io_uring/kbuf: export io_ring_buffer_select()

Export io_ring_buffer_select() so that it may be used by callers who
pass in a pinned bufring without needing to grab the io_uring mutex.

This is a preparatory patch that will be needed by fuse io-uring, which
will need to select a buffer from a kernel-managed bufring while the
uring mutex may already be held by in-progress commits, and may need to
select a buffer in atomic contexts.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Link: https://patch.msgid.link/20260306003224.3620942-8-joannelkoong@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: joannekoong

include/linux/io_uring/cmd.h

@@ -102,6 +102,10 @@ int io_uring_kmbuf_recycle(struct io_uring_cmd *cmd, unsigned int buf_group,
 
 bool io_uring_is_kmbuf_ring(struct io_uring_cmd *cmd, unsigned int buf_group,
 			    unsigned int issue_flags);
+
+struct io_br_sel io_ring_buffer_select(struct io_kiocb *req, size_t *len,
+				       struct io_buffer_list *bl,
+				       unsigned int issue_flags);
 #else
 static inline int
 io_uring_cmd_import_fixed(u64 ubuf, unsigned long len, int rw,
@@ -170,6 +174,16 @@ static inline bool io_uring_is_kmbuf_ring(struct io_uring_cmd *cmd,
 {
 	return false;
 }
+static inline struct io_br_sel io_ring_buffer_select(struct io_kiocb *req,
+						     size_t *len,
+						     struct io_buffer_list *bl,
+						     unsigned int issue_flags)
+{
+	struct io_br_sel sel = {
+		.val = -EOPNOTSUPP,
+	};
+	return sel;
+}
 #endif
 
 static inline struct io_uring_cmd *io_uring_cmd_from_tw(struct io_tw_req tw_req)

io_uring/kbuf.c

@@ -239,9 +239,9 @@ static bool io_should_commit(struct io_kiocb *req, struct io_buffer_list *bl,
 	return false;
 }
 
-static struct io_br_sel io_ring_buffer_select(struct io_kiocb *req, size_t *len,
-					      struct io_buffer_list *bl,
-					      unsigned int issue_flags)
+struct io_br_sel io_ring_buffer_select(struct io_kiocb *req, size_t *len,
+				       struct io_buffer_list *bl,
+				       unsigned int issue_flags)
 {
 	struct io_uring_buf_ring *br = bl->buf_ring;
 	__u16 tail, head = bl->head;
@@ -275,6 +275,7 @@ static struct io_br_sel io_ring_buffer_select(struct io_kiocb *req, size_t *len,
 	}
 	return sel;
 }
+EXPORT_SYMBOL_GPL(io_ring_buffer_select);
 
 struct io_br_sel io_buffer_select(struct io_kiocb *req, size_t *len,
 				  unsigned buf_group, unsigned int issue_flags)