Re: [PATCH v4 14/14] io_uring/rsrc: add dmabuf backed registered buffers

On Wed, Jul 29, 2026 at 7:37=E2=80=AFPM Pavel Begunkov <asml.silence@gmail.=
com> wrote:
> >> +static int io_import_dmabuf(struct io_kiocb *req,
> >> +                       int ddir, struct iov_iter *iter,
> >> +                       struct io_mapped_ubuf *imu,
> >> +                       size_t len, size_t offset,
> >> +                       unsigned issue_flags)
> >> +{
> >> +    struct io_regbuf_dma *db =3D imu->priv;
> >> +    struct dma_buf_io_map *map;
> >> +
> >> +    if (!IS_ENABLED(CONFIG_DMA_SHARED_BUFFER))
> >> +            return -EOPNOTSUPP;
> >> +    if (!len)
> >> +            return -EFAULT;
> >> +    if (req->file !=3D db->target_file)
> >> +            return -EBADF;
> >> +
> >> +    if (req->flags & REQ_F_DROP_DMABUF) {
> >> +            map =3D req->dmabuf_map;
> >> +            goto init_iter;
> >> +    }
> >
> > O_DIRECT is checked only during registration; we should recheck
> > (file->f_flags & O_DIRECT) per request.
>
> Nobody should be able to clear O_DIRECT, unless I missed something?
> And fwiw, io_uring wouldn't be the right place to do it.
>

fcntl(fd, F_SETFL, flags & ~O_DIRECT) on an already registered, already
open fd succeeds. The consequence is that subsequent I/Os switch to
buffered I/O and cause silent data loss. Something on this path needs
to reject this combination.

> --
> Pavel Begunkov
>
>