Re: [PATCH v4 19/25] fuse: add io-uring kernel-managed buffer ring

[Joanne Koong <joannelkoong@gmail.com>]

On Wed, Jan 28, 2026 at 1:44 PM Bernd Schubert <bernd@bsbernd.com> wrote:
>
>
>
> On 1/17/26 00:30, Joanne Koong wrote:
> > Add io-uring kernel-managed buffer ring capability for fuse daemons
> > communicating through the io-uring interface.
> >
> > This has two benefits:
> > a) eliminates the overhead of pinning/unpinning user pages and
> > translating virtual addresses for every server-kernel interaction
> >
> > b) reduces the amount of memory needed for the buffers per queue and
> > allows buffers to be reused across entries. Incremental buffer
> > consumption, when added, will allow a buffer to be used across multiple
> > requests.
> >
> > Buffer ring usage is set on a per-queue basis. In order to use this, the
> > daemon needs to have preregistered a kernel-managed buffer ring and a
> > fixed buffer at index 0 that will hold all the headers, and set the
> > "use_bufring" field during registration. The kernel-managed buffer ring
> > will be pinned for the lifetime of the connection.
> >
> > Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
> > ---
> >  fs/fuse/dev_uring.c       | 412 ++++++++++++++++++++++++++++++++------
> >  fs/fuse/dev_uring_i.h     |  31 ++-
> >  include/uapi/linux/fuse.h |  15 +-
> >  3 files changed, 389 insertions(+), 69 deletions(-)
> >
> > diff --git a/fs/fuse/dev_uring.c b/fs/fuse/dev_uring.c
> > index b57871f92d08..40e8c2e6b77c 100644
> > --- a/fs/fuse/dev_uring.c
> > +++ b/fs/fuse/dev_uring.c

> > @@ -1305,7 +1311,14 @@ struct fuse_uring_cmd_req {
> >
> >       /* queue the command is for (queue index) */
> >       uint16_t qid;
> > -     uint8_t padding[6];
> > +
> > +     union {
> > +             struct {
> > +                     uint16_t flags;
> > +             } init;
> > +     };
> > +
>
> I won't manage to review everything of this patch today, but just
> noticed this. There is already an unused flags, why don't you use that?
> I had edded it exactly for such things.

Oh nice, I missed seeing that. I'll just use that flags variable then.

Thanks,
Joanne
>
> > +     uint8_t padding[4];
> >  };
> >
> >  #endif /* _LINUX_FUSE_H */
>
> Thanks,
> Bernd