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

[Pavel Begunkov]

On 7/29/26 17:52, Anuj gupta wrote:
> On Wed, Jul 29, 2026 at 7:37 PM Pavel Begunkov <asml.silence at 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 = imu->priv;
>>>> +    struct dma_buf_io_map *map;
>>>> +
>>>> +    if (!IS_ENABLED(CONFIG_DMA_SHARED_BUFFER))
>>>> +            return -EOPNOTSUPP;
>>>> +    if (!len)
>>>> +            return -EFAULT;
>>>> +    if (req->file != db->target_file)
>>>> +            return -EBADF;
>>>> +
>>>> +    if (req->flags & REQ_F_DROP_DMABUF) {
>>>> +            map = 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

Very exciting.

> buffered I/O and cause silent data loss. Something on this path needs
> to reject this combination.

Yeah, I'll fix it, thanks

-- 
Pavel Begunkov