Le mercredi 27 avril 2022 à 13:31 +0900, Tomasz Figa a écrit :
> Hi Nicolas, Sebastian,
>
> On Tue, Apr 26, 2022 at 9:58 PM Nicolas Dufresne
> <nicolas.dufresne@xxxxxxxxxxxxx> wrote:
> >
> > From: Sebastian Fricke <sebastian.fricke@xxxxxxxxxxxxx>
> >
> > Using V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF flag without specifying the
> > subsystem flag VB2_V4L2_FL_SUPPORTS_M2M_HOLD_CAPTURE_BUF, results in
> > silently ignoring it.
> > Warn the user via a debug print when the flag is requested but ignored
> > by the videobuf2 framework.
> >
> > Signed-off-by: Sebastian Fricke <sebastian.fricke@xxxxxxxxxxxxx>
> > Signed-off-by: Nicolas Dufresne <nicolas.dufresne@xxxxxxxxxxxxx>
> > Reviewed-by: Ezequiel Garcia <ezequiel@xxxxxxxxxxxxxxxxxxxx>
> > ---
> > drivers/media/common/videobuf2/videobuf2-v4l2.c | 7 ++++++-
> > 1 file changed, 6 insertions(+), 1 deletion(-)
> >
>
> Thanks for the patch. Please see my comments inline.
>
> > diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> > index 6edf4508c636..812c8d1962e0 100644
> > --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> > +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> > @@ -329,8 +329,13 @@ static int vb2_fill_vb2_v4l2_buffer(struct vb2_buffer *vb, struct v4l2_buffer *b
> > */
> > vbuf->flags &= ~V4L2_BUF_FLAG_TIMECODE;
> > vbuf->field = b->field;
> > - if (!(q->subsystem_flags & VB2_V4L2_FL_SUPPORTS_M2M_HOLD_CAPTURE_BUF))
> > + if (!(q->subsystem_flags & VB2_V4L2_FL_SUPPORTS_M2M_HOLD_CAPTURE_BUF)) {
> > + if (vbuf->flags & V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF)
> > + dprintk(q, 1,
> > + "Request holding buffer (%d), unsupported on output queue\n",
> > + b->index);
>
> I wonder if we shouldn't just fail such a QBUF operation. Otherwise
> the application would get unexpected behavior from the kernel.
> Although it might be too late to do it now if there are applications
> that rely on this implicit ignore...
In the context of this patchset, the statu quo seems to be the logical thing to
do. We can raise this up in a separate thread. The side effect is of course
confusing for developers, but it is hard for me to tell if a hard failure may
break an existing software.
regards,
Nicolas
>
> Best regards,
> Tomasz
