On Sunday 24 October 2010 18:52:09 Pawel Osciak wrote: > On Fri, Oct 22, 2010 at 17:18, Mauro Carvalho Chehab <mchehab@xxxxxxxxxx> wrote: > > Em 06-09-2010 03:53, Marek Szyprowski escreveu: > >> From: Pawel Osciak <p.osciak@xxxxxxxxxxx> > >> > >> VIDIOC_STREAMON should return EBUSY if streaming is already active. > >> > >> Signed-off-by: Pawel Osciak <p.osciak@xxxxxxxxxxx> > >> Signed-off-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx> > >> Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> > >> --- > >> Documentation/DocBook/v4l/vidioc-streamon.xml | 7 +++++++ > >> 1 files changed, 7 insertions(+), 0 deletions(-) > >> > >> diff --git a/Documentation/DocBook/v4l/vidioc-streamon.xml > >> b/Documentation/DocBook/v4l/vidioc-streamon.xml index e42bff1..fdbd8d8 > >> 100644 > >> --- a/Documentation/DocBook/v4l/vidioc-streamon.xml > >> +++ b/Documentation/DocBook/v4l/vidioc-streamon.xml > >> @@ -93,6 +93,13 @@ synchronize with other events.</para> > >> been allocated (memory mapping) or enqueued (output) yet.</para> > >> </listitem> > >> </varlistentry> > >> + <varlistentry> > >> + <term><errorcode>EBUSY</errorcode></term> > >> + <listitem> > >> + <para><constant>VIDIOC_STREAMON</constant> called, but > >> + streaming I/O already active.</para> > >> + </listitem> > >> + </varlistentry> > >> </variablelist> > >> </refsect1> > >> </refentry> > > > > I'm in doubt about this patch. I don't see any problem on just return 0 > > if stream is active. > > > > Actually, I think that this patch may break some applications, as there > > are some cases where stream may start even without streamon (like via > > read() method). > > A quick grep over the media directory reveals that many drivers > (including videobuf_streamon) return EBUSY for some cases. This patch > was not intended to introduce something new to the API. I just wanted > to document an undocumented return value. How should the EBUSY return > be interpreted? Or should we get rid of it? I think the patch makes sense. As you mention many drivers already implement this behaviour, so this mostly clarifies the API. Calling VIDIOC_STREAMON on an already streaming file handle isn't something applications should do in the first place anyway. -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
