From: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
To: Hans Verkuil <hverkuil@xs4all.nl>
Cc: James Harper <james@ejbdigital.com.au>,
"linux-media@vger.kernel.org" <linux-media@vger.kernel.org>
Subject: Re: [PATCH 1/3] vb2: fix VBI/poll regression
Date: Sat, 20 Sep 2014 07:04:12 -0300 [thread overview]
Message-ID: <20140920070412.6486a728@recife.lan> (raw)
In-Reply-To: <541D4568.2020605@xs4all.nl>
Em Sat, 20 Sep 2014 11:14:16 +0200
Hans Verkuil <hverkuil@xs4all.nl> escreveu:
> On 09/20/2014 11:08 AM, James Harper wrote:
> >>
> >> 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.
> >>
> >
> > What (mis)behaviour would this cause in userspace application?
>
> If an app would rely on poll to return POLLERR to do the initial STREAMON
> (seen in e.g. alevt) or to do the initial QBUF (I'm not aware of any apps
> that do that, but they may exist), then that will currently fail with vb2
> because poll() will just wait indefinitely in those cases.
>
> Regards,
>
> Hans
> --
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next prev parent reply other threads:[~2014-09-20 10:04 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-20 8:56 [PATCH 0/3] vb2: fix VBI/poll regression Hans Verkuil
2014-09-20 8:56 ` [PATCH 1/3] " Hans Verkuil
2014-09-20 9:08 ` James Harper
2014-09-20 9:14 ` Hans Verkuil
2014-09-20 10:04 ` Mauro Carvalho Chehab [this message]
2014-09-20 10:08 ` Mauro Carvalho Chehab
2014-09-20 10:14 ` Mauro Carvalho Chehab
2014-09-20 18:32 ` Laurent Pinchart
2014-09-20 19:12 ` Hans Verkuil
2014-09-20 8:56 ` [PATCH 2/3] DocBook media: fix the poll() 'no QBUF' documentation Hans Verkuil
2014-09-20 18:35 ` Laurent Pinchart
2014-09-20 8:56 ` [PATCH 3/3] DocBook media: improve the poll() documentation Hans Verkuil
2014-09-20 9:51 ` [PATCH 0/3] vb2: fix VBI/poll regression Mauro Carvalho Chehab
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