[RFC] vb2: regression fix for vbi capture & poll
Commit Message
(My proposal to fix this. Note that it is untested, I plan to do that this
evening)
Commit 9241650d62f7 broke vbi capture applications that expect POLLERR to be
returned if STREAMON wasn't called.
Rather than checking whether buffers were queued AND vb2 was not yet streaming,
just check whether streaming is in progress and return POLLERR if not.
This change makes it impossible to poll in one thread and call STREAMON in
another, but doing that breaks existing applications and is also not according
to the spec. So be it.
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
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Comments
Hi Hans,
Thank you for the patch.
On Tuesday 16 September 2014 12:28:50 Hans Verkuil wrote:
> (My proposal to fix this. Note that it is untested, I plan to do that this
> evening)
>
> Commit 9241650d62f7 broke vbi capture applications that expect POLLERR to be
> returned if STREAMON wasn't called.
>
> Rather than checking whether buffers were queued AND vb2 was not yet
> streaming, just check whether streaming is in progress and return POLLERR
> if not.
>
> This change makes it impossible to poll in one thread and call STREAMON in
> another, but doing that breaks existing applications and is also not
> according to the spec. So be it.
I like this approach better than reverting the offending patch, as it doesn't
break my use case :-)
If we decide that this is the right fix, we should update the V4L2
specification to reflect that.
I've proposed an alternative solution in a reply to the "[PATCH/RFC v2 1/2]
v4l: vb2: Don't return POLLERR during transient buffer underruns" mail thread.
I think I like this patch better, as the behaviour is simpler, even if it
doesn't strictly conform to the spec.
> Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
>
> diff --git a/drivers/media/v4l2-core/videobuf2-core.c
> b/drivers/media/v4l2-core/videobuf2-core.c index 7e6aff6..0452fb2 100644
> --- a/drivers/media/v4l2-core/videobuf2-core.c
> +++ b/drivers/media/v4l2-core/videobuf2-core.c
> @@ -2583,10 +2583,10 @@ 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;
>
> /*
@@ -2583,10 +2583,10 @@ 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;
/*