[libcamera-devel] [PATCH 2/3] libcamera: V4L2Device: Use std::vector for v4l2_ext_control in setControls()

[Hirokazu Honda]

On Wed, Apr 14, 2021 at 7:14 AM Kieran Bingham
<kieran.bingham at ideasonboard.com> wrote:
>
> Hi Hiro,
>
> On 13/04/2021 07:19, Hirokazu Honda wrote:
> > The original code uses Variable-Length-Array, which is not
> > officially supported in C++. This replaces the array with
> > std::vector.
> > ---
> >  src/libcamera/v4l2_device.cpp | 18 +++++++++---------
> >  1 file changed, 9 insertions(+), 9 deletions(-)
> >
> > diff --git a/src/libcamera/v4l2_device.cpp b/src/libcamera/v4l2_device.cpp
> > index 78c289c2..8625dde8 100644
> > --- a/src/libcamera/v4l2_device.cpp
> > +++ b/src/libcamera/v4l2_device.cpp
> > @@ -280,12 +280,11 @@ ControlList V4L2Device::getControls(const std::vector<uint32_t> &ids)
> >   */
> >  int V4L2Device::setControls(ControlList *ctrls)
> >  {
> > -     unsigned int count = ctrls->size();
> > -     if (count == 0)
> > +     if (ctrls->empty())
> >               return 0;
> >
> > -     struct v4l2_ext_control v4l2Ctrls[count];
> > -     memset(v4l2Ctrls, 0, sizeof(v4l2Ctrls));
> > +     std::vector<v4l2_ext_control> v4l2Ctrls(ctrls->size());
> > +     memset(v4l2Ctrls.data(), 0, v4l2Ctrls.size());
>
> Does the vector not initialise in anyway ?
>
> Looking at https://www.cplusplus.com/reference/vector/vector/vector/
> this must be using the fill(2) constructor.
>
> I suspect if nothing is provided, it won't fill, so perhaps it's not
> initialised, but if that's the case, I wonder if the right way to
> construct this is more like:
>
>         std::vector<v4l2_ext_control> v4l2Ctrls(ctrls->size(), {});

As replied to 1/3, I don't trust the zero initialization by {}.
So I would rather use std::memset.

Best Regards,
-Hiro
>
> But I'm not particular certain.
>
> Otherwise, this looks Ok to me...
>
> Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
>
> >
> >       unsigned int i = 0;
> >       for (auto &ctrl : *ctrls) {
> > @@ -332,15 +331,15 @@ int V4L2Device::setControls(ControlList *ctrls)
> >
> >       struct v4l2_ext_controls v4l2ExtCtrls = {};
> >       v4l2ExtCtrls.which = V4L2_CTRL_WHICH_CUR_VAL;
> > -     v4l2ExtCtrls.controls = v4l2Ctrls;
> > -     v4l2ExtCtrls.count = count;
> > +     v4l2ExtCtrls.controls = v4l2Ctrls.data();
> > +     v4l2ExtCtrls.count = v4l2Ctrls.size();
> >
> >       int ret = ioctl(VIDIOC_S_EXT_CTRLS, &v4l2ExtCtrls);
> >       if (ret) {
> >               unsigned int errorIdx = v4l2ExtCtrls.error_idx;
> >
> >               /* Generic validation error. */
> > -             if (errorIdx == 0 || errorIdx >= count) {
> > +             if (errorIdx == 0 || errorIdx >= v4l2Ctrls.size()) {
> >                       LOG(V4L2, Error) << "Unable to set controls: "
> >                                        << strerror(-ret);
> >                       return -EINVAL;
> > @@ -349,11 +348,12 @@ int V4L2Device::setControls(ControlList *ctrls)
> >               /* A specific control failed. */
> >               LOG(V4L2, Error) << "Unable to set control " << errorIdx
> >                                << ": " << strerror(-ret);
> > -             count = errorIdx - 1;
> > +
> > +             v4l2Ctrls.resize(errorIdx);
> >               ret = errorIdx;
> >       }
> >
> > -     updateControls(ctrls, v4l2Ctrls, count);
> > +     updateControls(ctrls, v4l2Ctrls.data(), v4l2Ctrls.size());
> >
> >       return ret;
> >  }
> >
>
> --
> Regards
> --
> Kieran