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>
---
 include/linux/io_uring/buf.h | 25 +++++++++++++++++++++++++
 io_uring/kbuf.c              |  8 +++++---
 2 files changed, 30 insertions(+), 3 deletions(-)
 create mode 100644 include/linux/io_uring/buf.h

diff --git a/include/linux/io_uring/buf.h b/include/linux/io_uring/buf.h
new file mode 100644
index 000000000000..3f7426ced3eb
--- /dev/null
+++ b/include/linux/io_uring/buf.h
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _LINUX_IO_URING_BUF_H
+#define _LINUX_IO_URING_BUF_H
+
+#include <linux/io_uring_types.h>
+
+#if defined(CONFIG_IO_URING)
+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 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 /* CONFIG_IO_URING */
+
+#endif /* _LINUX_IO_URING_BUF_H */
diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
index d86199ac3377..d2a660ecc7ac 100644
--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -9,6 +9,7 @@
 #include <linux/poll.h>
 #include <linux/vmalloc.h>
 #include <linux/io_uring.h>
+#include <linux/io_uring/buf.h>
 #include <linux/io_uring/cmd.h>
 
 #include <uapi/linux/io_uring.h>
@@ -226,9 +227,9 @@ 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;
@@ -261,6 +262,7 @@ 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)
-- 
2.47.3