On Friday 06 June 2014 11:58:18 Hans Verkuil wrote: > On 06/06/2014 11:50 AM, Hans de Goede wrote: > > Hi, > > > > On 06/05/2014 02:23 PM, Laurent Pinchart wrote: > >> The V4L2 specification states that > >> > >> "When the application did not call VIDIOC_QBUF or VIDIOC_STREAMON yet > >> the poll() function succeeds, but sets the POLLERR flag in the revents > >> field." > >> > >> The vb2_poll() function sets POLLERR when the queued buffers list is > >> empty, regardless of whether this is caused by the stream not being > >> active yet, or by a transient buffer underrun. > >> > >> Bring the implementation in line with the specification by returning > >> POLLERR only when the queue is not streaming. Buffer underruns during > >> streaming are not treated specially anymore and just result in poll() > >> blocking until the next event. > > > > After your patch the implementation is still not inline with the spec, > > queuing buffers, then starting a thread doing the poll, then doing the > > streamon in the main thread will still cause the poll to return POLLERR, > > even though buffers are queued, which according to the spec should be > > enough for the poll to block. > > > > The correct check would be: > > > > if (list_empty(&q->queued_list) && !vb2_is_streaming(q)) > > > > eturn res | POLLERR; > > Good catch! I should have seen that :-( I'll update the patch accordingly. > v4l2-compliance should certainly be extended to test this as well. > > Regards, > > Hans > > > Regards, > > > > Hans > > > >> Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> > >> Acked-by: Hans Verkuil <hans.verkuil@xxxxxxxxx> > >> --- > >> > >> drivers/media/v4l2-core/videobuf2-core.c | 4 ++-- > >> 1 file changed, 2 insertions(+), 2 deletions(-) > >> > >> diff --git a/drivers/media/v4l2-core/videobuf2-core.c > >> b/drivers/media/v4l2-core/videobuf2-core.c index 349e659..fd428e0 100644 > >> --- a/drivers/media/v4l2-core/videobuf2-core.c > >> +++ b/drivers/media/v4l2-core/videobuf2-core.c > >> @@ -2533,9 +2533,9 @@ unsigned int vb2_poll(struct vb2_queue *q, struct > >> file *file, poll_table *wait)>> > >> } > >> > >> /* > >> > >> - * There is nothing to wait for if no buffers have already been queued. > >> + * There is nothing to wait for if the queue isn't streaming. > >> > >> */ > >> > >> - if (list_empty(&q->queued_list)) > >> + if (!vb2_is_streaming(q)) > >> > >> return res | POLLERR; > >> > >> if (list_empty(&q->done_list)) -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
