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

[Joanne Koong <joannelkoong@gmail.com>]

On Thu, Jan 8, 2026 at 12:34 PM Caleb Sander Mateos
<csander@purestorage.com> wrote:
>
> 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?

Oh interesting... I see struct io_kiocb defined in
include/linux/io_uring_types.h, so I assumed this was fine to use.
Hmm, we could wrap this in io_uring_cmd * instead, but that adds an
extra layer and I think it clashes with the philosophy of io_uring_cmd
being a "general user interface" (or maybe my interpretation of
io_uring_cmd is incorrect) whereas this api is pretty io-uring
internal specific (eg bypasses the io ring lock which means it'll be
responsible for having to do its own synchronization, passing the
io_buffer_list pointer directly, etc.).

Thanks,
Joanne

>
> 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 */