Re: [PATCHv2 1/2] v4l2-ioctl: simplify code

Mauro Carvalho Chehab
2016-04-13T22:09:43Z

Em Wed, 13 Apr 2016 23:51:45 +0200
Hans Verkuil <hverkuil@xs4all.nl> escreveu:

> On 04/13/2016 09:57 PM, Mauro Carvalho Chehab wrote:
> > Em Mon, 21 Mar 2016 09:47:59 +0100
> > Hans Verkuil <hverkuil@xs4all.nl> escreveu:
> >
> >> From: Hans Verkuil <hans.verkuil@cisco.com>
> >>
> >> Instead of a big if at the beginning, just check if g_selection == NULL
> >> and call the cropcap op immediately and return the result.
> >>
> >> No functional changes in this patch.
> >
> > Hmm... not true. See below.
> >
> >>
> >> Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
> >
> > You forgot to add Miklas review here.
> >
> >> ---
> >> drivers/media/v4l2-core/v4l2-ioctl.c | 51 ++++++++++++++++++++----------------
> >> 1 file changed, 29 insertions(+), 22 deletions(-)
> >>
> >> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> >> index 6bf5a3e..3cf8d3a 100644
> >> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> >> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> >> @@ -2160,33 +2160,40 @@ static int v4l_cropcap(const struct v4l2_ioctl_ops *ops,
> >> struct file *file, void *fh, void *arg)
> >> {
> >> struct v4l2_cropcap *p = arg;
> >> + struct v4l2_selection s = { .type = p->type };
> >> + int ret;
> >>
> >> - if (ops->vidioc_g_selection) {
> >> - struct v4l2_selection s = { .type = p->type };
> >> - int ret;
> >> + if (ops->vidioc_g_selection == NULL) {
> >> + /*
> >> + * The determine_valid_ioctls() call already should ensure
> >> + * that ops->vidioc_cropcap != NULL, but just in case...
> >> + */
> >> + if (ops->vidioc_cropcap)
> >> + return ops->vidioc_cropcap(file, fh, p);
> >> + return -ENOTTY;
> >
> > Actually, before this patch, the logic would be doing, instead:
> >
> > /* setting trivial pixelaspect */
> > p->pixelaspect.numerator = 1;
> > p->pixelaspect.denominator = 1;
> >
> > if (ops->vidioc_cropcap)
> > return ops->vidioc_cropcap(file, fh, p);
> >
> > return 0;
> >
> > With is not the same as what's there. So, there are actually two
> > differences:
> >
> > 1) it will now return -ENOTTY if !ops->vidioc_cropcap instead of 0.
> >
> > (returning -ENOTTY is probably the best, but this is a fixup change,
> > and a functional change, so, should be in a separate patch, if needed)
> >
> > 2) pixel numerator/denominator is not initialized in the new code.
> >
> > Ok, maybe all drivers would be setting numerator and denominator to 1
> > as default, so the code won't need to do it, but:
> >
> > a) This is not a trivial assumption by looking only on this patch;
> >
> > b) It sounds risky to not setup denominator, as, if a driver is not
> > initializing it, it could cause a division by zero at userspace.
> >
> > So, I would prefer to keep initializing numerator/denominator here.
> >
> > As this is just a cleanup patch, I'm skipping it for now.
>
> I'm confused, you say you're skipping it, yet it is merged. But patch 2/2
> (v4l2-ioctl: improve cropcap handling) isn't merged.
>
> I refrain from commenting on the points you raised until I know what's going
> on here.

Sorry, my mistake. I'll revert it. Please send patch 2/2 after
we fix the issues on this one.

>
> Regards,
>
> Hans
>
> >
> > Btw, IMHO, the best here would be to split the logic that it is called
> > if ops->vidioc_g_selection is not NULL on a separate function. That
> > would make the logic even clearer, and would help to show that it will
> > be handling the logic below "setting trivial pixelaspect" the same way.
> >
> > Regards,
> > Mauro
> >
> >> + }
> >>
> >> - /* obtaining bounds */
> >> - if (V4L2_TYPE_IS_OUTPUT(p->type))
> >> - s.target = V4L2_SEL_TGT_COMPOSE_BOUNDS;
> >> - else
> >> - s.target = V4L2_SEL_TGT_CROP_BOUNDS;
> >> + /* obtaining bounds */
> >> + if (V4L2_TYPE_IS_OUTPUT(p->type))
> >> + s.target = V4L2_SEL_TGT_COMPOSE_BOUNDS;
> >> + else
> >> + s.target = V4L2_SEL_TGT_CROP_BOUNDS;
> >>
> >> - ret = ops->vidioc_g_selection(file, fh, &s);
> >> - if (ret)
> >> - return ret;
> >> - p->bounds = s.r;
> >> + ret = ops->vidioc_g_selection(file, fh, &s);
> >> + if (ret)
> >> + return ret;
> >> + p->bounds = s.r;
> >>
> >> - /* obtaining defrect */
> >> - if (V4L2_TYPE_IS_OUTPUT(p->type))
> >> - s.target = V4L2_SEL_TGT_COMPOSE_DEFAULT;
> >> - else
> >> - s.target = V4L2_SEL_TGT_CROP_DEFAULT;
> >> + /* obtaining defrect */
> >> + if (V4L2_TYPE_IS_OUTPUT(p->type))
> >> + s.target = V4L2_SEL_TGT_COMPOSE_DEFAULT;
> >> + else
> >> + s.target = V4L2_SEL_TGT_CROP_DEFAULT;
> >>
> >> - ret = ops->vidioc_g_selection(file, fh, &s);
> >> - if (ret)
> >> - return ret;
> >> - p->defrect = s.r;
> >> - }
> >> + ret = ops->vidioc_g_selection(file, fh, &s);
> >> + if (ret)
> >> + return ret;
> >> + p->defrect = s.r;
> >>
> >> /* setting trivial pixelaspect */
> >> p->pixelaspect.numerator = 1;
> >
> >
>

--
Thanks,
Mauro