Re: [git:media_tree/devel] [media] BZ#84401: Revert "[media] v4l: vb2: Don't return POLLERR during transient buffer underruns"

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

Hi Mauro,

On Tuesday 16 September 2014 02:05:38 Mauro Carvalho Chehab wrote:
> This is an automatic generated email to let you know that the following
> patch were queued at the http://git.linuxtv.org/media_tree.git tree:
> 
> Subject: [media] BZ#84401: Revert "[media] v4l: vb2: Don't return POLLERR
> during transient buffer underruns" Author:  Mauro Carvalho Chehab
> <m.chehab@samsung.com>
> Date:    Mon Sep 15 20:58:01 2014 -0300
> 
> This reverts commit 9241650d62f79a3da01f1d5e8ebd195083330b75.
> 
> The commit 9241650d62f7 was meant to solve an issue with Gstreamer
> version 0.10 with libv4l 1.2, where a fixup patch for DQBUF exposed
> a bad behavior ag Gstreamer.
> 
> It does that by returning POLERR if VB2 is not streaming.
> 
> However, it broke VBI userspace support on alevt and mtt (and maybe
> other VBI apps), as they rely on the old behavior.
> 
> Due to that, we need to roll back and restore the previous behavior.
> 
> It means that there are still some potential regressions by reverting it,
> but those are known to occur only if:
> 	- libv4l is version 1.2 or upper (due to DQBUF fixup);
> 	- Gstreamer version 1.2 or before are being used, as this bug
> got fixed on Gstreamer 1.4.
> 
> As both libv4l 1.2 and Gstreamer version 1.4 were released about the same
> time, and the fix went only on Kernel 3.16 and were not backported to
> stable, it is very unlikely that reverting it would cause much harm.
> 
> For more details, see:
> 	https://bugzilla.kernel.org/show_bug.cgi?id=84401
> 
> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Cc: Hans Verkuil <hans.verkuil@cisco.com>
> Cc: Pawel Osciak <pawel@osciak.com>
> Cc: Nicolas Dufresne <nicolas.dufresne@collabora.com>
> Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
> 
>  drivers/media/v4l2-core/videobuf2-core.c |    6 +++---
>  1 files changed, 3 insertions(+), 3 deletions(-)
> 
> ---
> 
> http://git.linuxtv.org/media_tree.git?a=commitdiff;h=e0857d1d1af8478b33e63db
> b22bb2160a807d868
> 
> diff --git a/drivers/media/v4l2-core/videobuf2-core.c
> b/drivers/media/v4l2-core/videobuf2-core.c index 7e6aff6..7387821 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 no buffer has been queued
> +	 * or if the error flag is set.
>  	 */
> -	if ((list_empty(&q->queued_list) && !vb2_is_streaming(q)) || q->error)
> +	if ((list_empty(&q->queued_list) || q->error)

This has probably not been compile-tested.

>  		return res | POLLERR;
> 
>  	/*

-- 
Regards,

Laurent Pinchart