Re: [PATCH v1 09/30] io_uring: add io_uring_cmd_import_fixed_index()

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

On Thu, Dec 4, 2025 at 10:56 AM Joanne Koong <joannelkoong@gmail.com> wrote:
>
> On Wed, Dec 3, 2025 at 1:44 PM Caleb Sander Mateos
> <csander@purestorage.com> wrote:
> >
> > On Tue, Dec 2, 2025 at 4:36 PM Joanne Koong <joannelkoong@gmail.com> wrote:
> > >
> > > Add a new helper, io_uring_cmd_import_fixed_index(). This takes in a
> > > buffer index. This requires the buffer table to have been pinned
> > > beforehand. The caller is responsible for ensuring it does not use the
> > > returned iter after the buffer table has been unpinned.
> > >
> > > This is a preparatory patch needed for fuse-over-io-uring support, as
> > > the metadata for fuse requests will be stored at the last index, which
> > > will be different from the sqe's buffer index.
> > >
> > > Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
> > > ---
> > >  include/linux/io_uring/cmd.h | 10 ++++++++++
> > >  io_uring/rsrc.c              | 31 +++++++++++++++++++++++++++++++
> > >  io_uring/rsrc.h              |  2 ++
> > >  io_uring/uring_cmd.c         | 11 +++++++++++
> > >  4 files changed, 54 insertions(+)
> > >
> > > diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
> > > index 67331cae0a5a..b6dd62118311 100644
> > > --- a/io_uring/rsrc.c
> > > +++ b/io_uring/rsrc.c
> > > @@ -1156,6 +1156,37 @@ int io_import_reg_buf(struct io_kiocb *req, struct iov_iter *iter,
> > >         return io_import_fixed(ddir, iter, node->buf, buf_addr, len);
> > >  }
> > >
> > > +int io_import_reg_buf_index(struct io_kiocb *req, struct iov_iter *iter,
> > > +                           u16 buf_index, int ddir, unsigned issue_flags)
> > > +{
> > > +       struct io_ring_ctx *ctx = req->ctx;
> > > +       struct io_rsrc_node *node;
> > > +       struct io_mapped_ubuf *imu;
> > > +
> > > +       io_ring_submit_lock(ctx, issue_flags);
> > > +
> > > +       if (buf_index >= req->ctx->buf_table.nr ||
> >
> > This condition is already checked in io_rsrc_node_lookup() below.
>
> I think we still need this check here to differentiate between -EINVAL
> if buf_index is out of bounds and -EFAULT if the buf index was not out
> of bounds but the lookup returned NULL.

Is there a reason you prefer EINVAL over EFAULT? EFAULT seems
consistent with the errors returned from registered buffer lookups in
other cases.

Best,
Caleb

>
> >
> > > +           !(ctx->buf_table.flags & IO_RSRC_DATA_PINNED)) {
> > > +               io_ring_submit_unlock(ctx, issue_flags);
> > > +               return -EINVAL;
> > > +       }
> > > diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
> > > index 197474911f04..e077eba00efe 100644
> > > --- a/io_uring/uring_cmd.c
> > > +++ b/io_uring/uring_cmd.c
> > > @@ -314,6 +314,17 @@ int io_uring_cmd_import_fixed_vec(struct io_uring_cmd *ioucmd,
> > >  }
> > >  EXPORT_SYMBOL_GPL(io_uring_cmd_import_fixed_vec);
> > >
> > > +int io_uring_cmd_import_fixed_index(struct io_uring_cmd *ioucmd, u16 buf_index,
> > > +                                   int ddir, struct iov_iter *iter,
> > > +                                   unsigned int issue_flags)
> > > +{
> > > +       struct io_kiocb *req = cmd_to_io_kiocb(ioucmd);
> > > +
> > > +       return io_import_reg_buf_index(req, iter, buf_index, ddir,
> > > +                                      issue_flags);
> > > +}
> >
> > Probably would make sense to make this an inline function, since it
> > immediately defers to io_import_reg_buf_index().
>
> That makes sense to me, I'll make this change for v2.
>
> Thanks,
> Joanne
>
> >
> > Best,
> > Caleb