Re: [PATCH v3 10/25] io_uring/kbuf: export io_ring_buffer_select()

[Caleb Sander Mateos <csander@purestorage.com>]

On Mon, Dec 22, 2025 at 4:36 PM Joanne Koong <joannelkoong@gmail.com> wrote:
>
> 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,

I think struct io_kiocb isn't intended to be exposed outside of
io_uring internal code. Is there a reason not to instead expose a
wrapper function that takes struct io_uring_cmd * instead?

Best,
Caleb

> +                                      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 0524b22e60a5..3b9907f0a78e 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 <uapi/linux/io_uring.h>
>
> @@ -223,9 +224,9 @@ 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;
> @@ -259,6 +260,7 @@ 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
>