Re: [PATCH 1/3] vb2: fix VBI/poll regression

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Hans,

Thank you for the patch.

On Saturday 20 September 2014 10:56:13 Hans Verkuil wrote:
> From: Hans Verkuil <hans.verkuil@cisco.com>
> 
> 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@cisco.com>
> ---
>  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.

>  	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;

-- 
Regards,

Laurent Pinchart