On 09/20/2014 08:32 PM, Laurent Pinchart wrote:
> Hi Hans,
>
> Thank you for the patch.
>
> On Saturday 20 September 2014 10:56:13 Hans Verkuil wrote:
>> From: Hans Verkuil <hans.verkuil@xxxxxxxxx>
>>
>> The recent conversion of saa7134 to vb2 unconvered a poll() bug that
>> broke the teletext applications alevt and mtt. These applications
>> expect that calling poll() without having called VIDIOC_STREAMON will
>> cause poll() to return POLLERR. That did not happen in vb2.
>>
>> This patch fixes that behavior. It also fixes what should happen when
>> poll() is called when STREAMON is called but no buffers have been
>> queued. In that case poll() will also return POLLERR, but only for
>> capture queues since output queues will always return POLLOUT
>> anyway in that situation.
>>
>> This brings the vb2 behavior in line with the old videobuf behavior.
>>
>> Signed-off-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
>> ---
>> drivers/media/v4l2-core/videobuf2-core.c | 15 ++++++++++++---
>> include/media/videobuf2-core.h | 4 ++++
>> 2 files changed, 16 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/media/v4l2-core/videobuf2-core.c
>> b/drivers/media/v4l2-core/videobuf2-core.c index 7e6aff6..f3762a8 100644
>> --- a/drivers/media/v4l2-core/videobuf2-core.c
>> +++ b/drivers/media/v4l2-core/videobuf2-core.c
>> @@ -977,6 +977,7 @@ static int __reqbufs(struct vb2_queue *q, struct
>> v4l2_requestbuffers *req) * to the userspace.
>> */
>> req->count = allocated_buffers;
>> + q->waiting_for_buffers = !V4L2_TYPE_IS_OUTPUT(q->type);
>
> I think you also need to set waiting_for_buffers at STREAMOFF time, otherwise
> a STREAMOFF/STREAMON without a REQBUFS in-between won't work as expected.
Good catch. And I realized that it should also be set when CREATE_BUFS is called
instead of REQBUFS (although only when there are no buffers allocated yet).
Regards,
Hans
>
>> return 0;
>> }
>> @@ -1801,6 +1802,7 @@ static int vb2_internal_qbuf(struct vb2_queue *q,
>> struct v4l2_buffer *b) */
>> list_add_tail(&vb->queued_entry, &q->queued_list);
>> q->queued_count++;
>> + q->waiting_for_buffers = false;
>> vb->state = VB2_BUF_STATE_QUEUED;
>> if (V4L2_TYPE_IS_OUTPUT(q->type)) {
>> /*
>> @@ -2583,10 +2585,17 @@ unsigned int vb2_poll(struct vb2_queue *q, struct
>> file *file, poll_table *wait) }
>>
>> /*
>> - * There is nothing to wait for if no buffer has been queued and the
>> - * queue isn't streaming, or if the error flag is set.
>> + * There is nothing to wait for if the queue isn't streaming, or if the
>> + * error flag is set.
>> */
>> - if ((list_empty(&q->queued_list) && !vb2_is_streaming(q)) || q->error)
>> + if (!vb2_is_streaming(q) || q->error)
>> + return res | POLLERR;
>> + /*
>> + * For compatibility with vb1: if QBUF hasn't been called yet, then
>> + * return POLLERR as well. This only affects capture queues, output
>> + * queues will always initialize waiting_for_buffers to false.
>> + */
>> + if (q->waiting_for_buffers)
>> return res | POLLERR;
>>
>> /*
>> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
>> index 5a10d8d..84f790c 100644
>> --- a/include/media/videobuf2-core.h
>> +++ b/include/media/videobuf2-core.h
>> @@ -381,6 +381,9 @@ struct v4l2_fh;
>> * @start_streaming_called: start_streaming() was called successfully and
>> we * started streaming.
>> * @error: a fatal error occurred on the queue
>> + * @waiting_for_buffers: used in poll() to check if vb2 is still waiting
>> for + * buffers. Only set for capture queues if qbuf has not yet been +
>> * called since poll() needs to return POLLERR in that situation. *
>> @fileio: file io emulator internal data, used only if emulator is active
> *
>> @threadio: thread io internal data, used only if thread is active */
>> @@ -419,6 +422,7 @@ struct vb2_queue {
>> unsigned int streaming:1;
>> unsigned int start_streaming_called:1;
>> unsigned int error:1;
>> + unsigned int waiting_for_buffers:1;
>>
>> struct vb2_fileio_data *fileio;
>> struct vb2_threadio_data *threadio;
>
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