[libcamera-devel] [PATCH v2 2/3] libcamera: V4L2Device: Use std::vector for v4l2_ext_control in setControls()

[Hirokazu Honda]

Hi Laurent, thanks for reviewing.

On Tue, Apr 20, 2021 at 10:15 AM Laurent Pinchart
<laurent.pinchart at ideasonboard.com> wrote:
>
> Hi Hiro,
>
> Thank you for the patch.
>
> On Thu, Apr 15, 2021 at 01:48:53PM +0900, Hirokazu Honda wrote:
> > The original code uses Variable-Length-Array, which is not
> > officially supported in C++. This replaces the array with
> > std::vector.
> >
> > Signed-off-by: Hirokazu Honda <hiroh at chromium.org>
> > Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> > ---
> >  src/libcamera/v4l2_device.cpp | 32 +++++++++++++++-----------------
> >  1 file changed, 15 insertions(+), 17 deletions(-)
> >
> > diff --git a/src/libcamera/v4l2_device.cpp b/src/libcamera/v4l2_device.cpp
> > index ee8c3fed..5ec1b10e 100644
> > --- a/src/libcamera/v4l2_device.cpp
> > +++ b/src/libcamera/v4l2_device.cpp
> > @@ -279,12 +279,11 @@ 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());
>
> Is the memset() needed ? The std::vector constructor will default-insert
> the elements, which value-initializes them. If my interpretation of
> https://en.cppreference.com/w/cpp/language/value_initialization is
> correct, the elements will be zero-initialized.
>

value initialization in c++ fills zero to the first value in union.
If the second or later values in the union is large than the first
value, they are not zero-filled.
So I would use memset for a structure with a union.

> >
> >       unsigned int i = 0;
>
> Should we replace i with
>
>         v4l2_ext_control *v4l2Ctrl = v4l2Ctrls.data();
>
> and do a
>
>         v4l2Ctrl++;
>
> at the end of the loop ? That way we would ensure that i won't be used
> incorrectly (after being incremented) inside the loop.
>
> Apart from that,
>
> Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
>
> >       for (auto &ctrl : *ctrls) {
> > @@ -295,14 +294,14 @@ int V4L2Device::setControls(ControlList *ctrls)
> >                               << "Control " << utils::hex(id) << " not found";
> >                       return -EINVAL;
> >               }
> > -
> > -             v4l2Ctrls[i].id = id;
> > +             v4l2_ext_control &v4l2Ctrl = v4l2Ctrls[i++];
> > +             v4l2Ctrl.id = id;
> >
> >               /* Set the v4l2_ext_control value for the write operation. */
> >               ControlValue &value = ctrl.second;
> >               switch (iter->first->type()) {
> >               case ControlTypeInteger64:
> > -                     v4l2Ctrls[i].value64 = value.get<int64_t>();
> > +                     v4l2Ctrl.value64 = value.get<int64_t>();
> >                       break;
> >
> >               case ControlTypeByte: {
> > @@ -314,32 +313,30 @@ int V4L2Device::setControls(ControlList *ctrls)
> >                       }
> >
> >                       Span<uint8_t> data = value.data();
> > -                     v4l2Ctrls[i].p_u8 = data.data();
> > -                     v4l2Ctrls[i].size = data.size();
> > +                     v4l2Ctrl.p_u8 = data.data();
> > +                     v4l2Ctrl.size = data.size();
> >
> >                       break;
> >               }
> >
> >               default:
> >                       /* \todo To be changed to support strings. */
> > -                     v4l2Ctrls[i].value = value.get<int32_t>();
> > +                     v4l2Ctrl.value = value.get<int32_t>();
> >                       break;
> >               }
> > -
> > -             i++;
> >       }
> >
> >       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;
> > @@ -348,11 +345,12 @@ 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,
>
> Laurent Pinchart