Re: [PATCH v1 10/11] io_uring/kbuf: return buffer id in buffer selection

[Joanne Koong <joannelkoong@gmail.com>]

On Mon, Feb 9, 2026 at 4:53 PM Jens Axboe <axboe@kernel.dk> wrote:
>
> On 2/9/26 5:28 PM, Joanne Koong wrote:
> > Return the id of the selected buffer in io_buffer_select(). This is
> > needed for kernel-managed buffer rings to later recycle the selected
> > buffer.
> >
> > Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
> > ---
> >  include/linux/io_uring/cmd.h   | 2 +-
> >  include/linux/io_uring_types.h | 2 ++
> >  io_uring/kbuf.c                | 7 +++++--
> >  3 files changed, 8 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/linux/io_uring/cmd.h b/include/linux/io_uring/cmd.h
> > index d4b5943bdeb1..94df2bdebe77 100644
> > --- a/include/linux/io_uring/cmd.h
> > +++ b/include/linux/io_uring/cmd.h
> > @@ -71,7 +71,7 @@ void io_uring_cmd_issue_blocking(struct io_uring_cmd *ioucmd);
> >
> >  /*
> >   * Select a buffer from the provided buffer group for multishot uring_cmd.
> > - * Returns the selected buffer address and size.
> > + * Returns the selected buffer address, size, and id.
> >   */
> >  struct io_br_sel io_uring_cmd_buffer_select(struct io_uring_cmd *ioucmd,
> >                                           unsigned buf_group, size_t *len,
> > diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
> > index 36cc2e0346d9..5a56bb341337 100644
> > --- a/include/linux/io_uring_types.h
> > +++ b/include/linux/io_uring_types.h
> > @@ -100,6 +100,8 @@ struct io_br_sel {
> >               void *kaddr;
> >       };
> >       ssize_t val;
> > +     /* id of the selected buffer */
> > +     unsigned buf_id;
> >  };
>
> I'm probably missing something here, but why can't the caller just use
> req->buf_index for this?

The caller can, but from the caller side they only have access to the
cmd so they would need to do something like

struct io_kiocb *req = cmd_to_iocb_kiocb(ent->cmd);
buf_id = req->buf_index;

which may be kind of ugly with looking inside io-uring internals.
Maybe a helper here would be nicer, something like
io_uring_cmd_buf_id() or io_uring_req_buf_id(). It seemed cleaner to
me to just return the buf id as part of the io_br_sel struct, but I'm
happy to do it another way if you have a preference.

Thanks,
Joanne

>
> --
> Jens Axboe