Hi Hans,
On Monday 18 June 2012 13:30:18 Hans Verkuil wrote:
> On Mon June 18 2012 11:48:45 Laurent Pinchart wrote:
> > On Sunday 10 June 2012 12:25:41 Hans Verkuil wrote:
> > > From: Hans Verkuil <hans.verkuil@xxxxxxxxx>
> > >
> > > Signed-off-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
> > > ---
> > >
> > > drivers/media/video/v4l2-dev.c | 24 ++++++++++++++++++++++++
> > > 1 file changed, 24 insertions(+)
> > >
> > > diff --git a/drivers/media/video/v4l2-dev.c
> > > b/drivers/media/video/v4l2-dev.c index 1500208..5c0bb18 100644
> > > --- a/drivers/media/video/v4l2-dev.c
> > > +++ b/drivers/media/video/v4l2-dev.c
> > > @@ -46,6 +46,29 @@ static ssize_t show_index(struct device *cd,
> > >
> > > return sprintf(buf, "%i\n", vdev->index);
> > >
> > > }
> > >
> > > +static ssize_t show_debug(struct device *cd,
> > > + struct device_attribute *attr, char *buf)
> > > +{
> > > + struct video_device *vdev = to_video_device(cd);
> > > +
> > > + return sprintf(buf, "%i\n", vdev->debug);
> > > +}
> > > +
> > > +static ssize_t set_debug(struct device *cd, struct device_attribute
> > > *attr,
> > > + const char *buf, size_t len)
> > > +{
> > > + struct video_device *vdev = to_video_device(cd);
> > > + int res = 0;
> > > + u16 value;
> > > +
> > > + res = kstrtou16(buf, 0, &value);
> > > + if (res)
> > > + return res;
> > > +
> > > + vdev->debug = value;
> >
> > Can't this race with the various vdev->debug tests we have in the V4L core
> > ?
> Not really. You may have a short race where you set it, but some core test
> is just reading it and gets the old value. But that's no problem in this
> case. The worst that can happen is that you get one more or one less debug
> message in the log.
You test the debug value several times in the __video_do_ioctl() function. I
haven't checked in details whether changing the value between the two tests
could for instance lead to a KERN_CONT print without a previous non-KERN_CONT
message. That won't crash the machine :-) but it should still be avoided.
> It probably deserves a comment, though.
--
Regards,
Laurent Pinchart
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