[libcamera-devel] [PATCH v2 1/3] libcamera: V4L2Device: Use std::vector for v4l2_ext_control in getControls()

[Hirokazu Honda]

On Tue, Apr 20, 2021 at 9:59 AM Laurent Pinchart
<laurent.pinchart at ideasonboard.com> wrote:
>
> Hi Hiro,
>
> Thank you for the patch.
>
> On Thu, Apr 15, 2021 at 01:48:52PM +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>
> > ---
> >  src/libcamera/v4l2_device.cpp | 43 ++++++++++++++++-------------------
> >  1 file changed, 20 insertions(+), 23 deletions(-)
> >
> > diff --git a/src/libcamera/v4l2_device.cpp b/src/libcamera/v4l2_device.cpp
> > index 8fd79934..ee8c3fed 100644
> > --- a/src/libcamera/v4l2_device.cpp
> > +++ b/src/libcamera/v4l2_device.cpp
> > @@ -173,8 +173,7 @@ void V4L2Device::close()
> >   */
> >  ControlList V4L2Device::getControls(const std::vector<uint32_t> &ids)
>
> Unrelated to this patch, it occurred to me that the function should take
> a Span<const uint32_t> instead of a vector. Would you like to submit an
> additional patch ?
>

I tried this today. Span has an issue in a call like the following?

../src/libcamera/camera_sensor.cpp:804:43: error: no matching
constructor for initialization of 'Span<const uint32_t>' (aka
'Span<const unsigned int>')
        ControlList ctrls = subdev_->getControls({ V4L2_CID_PIXEL_RATE,


> >  {
> > -     unsigned int count = ids.size();
> > -     if (count == 0)
> > +     if (ids.empty())
> >               return {};
> >
> >       ControlList ctrls;
> > @@ -196,22 +195,25 @@ ControlList V4L2Device::getControls(const std::vector<uint32_t> &ids)
> >               ctrls.set(id, {});
> >       }
> >
> > -     struct v4l2_ext_control v4l2Ctrls[count];
> > -     memset(v4l2Ctrls, 0, sizeof(v4l2Ctrls));
> > -
> > -     unsigned int i = 0;
> > +     std::vector<v4l2_ext_control> v4l2Ctrls;
> > +     v4l2Ctrls.reserve(ctrls.size());
>
> This changes the behaviour slightly, in that if the ids vector contains
> the same ID multiple times, you'll allocate less memory here. That's
> actually better :-)
>
> >       for (auto &ctrl : ctrls) {
> >               unsigned int id = ctrl.first;
> >               const struct v4l2_query_ext_ctrl &info = controlInfo_[id];
> > +             v4l2_ext_control v4l2Ctrl;
> > +             memset(&v4l2Ctrl, 0, sizeof(v4l2Ctrl));
> >
> >               if (info.flags & V4L2_CTRL_FLAG_HAS_PAYLOAD) {
> > -                     ControlType type;
> > +                     ControlValue &value = ctrl.second;
> >
> >                       switch (info.type) {
> > -                     case V4L2_CTRL_TYPE_U8:
> > -                             type = ControlTypeByte;
> > +                     case V4L2_CTRL_TYPE_U8: {
> > +                             value.reserve(ControlTypeByte, true, info.elems);
> > +                             Span<uint8_t> data = value.data();
> > +                             v4l2Ctrl.p_u8 = data.data();
> > +                             v4l2Ctrl.size = data.size();
> >                               break;
> > -
> > +                     }
> >                       default:
> >                               LOG(V4L2, Error)
> >                                       << "Unsupported payload control type "
> > @@ -219,29 +221,23 @@ ControlList V4L2Device::getControls(const std::vector<uint32_t> &ids)
> >                               return {};
> >                       }
> >
> > -                     ControlValue &value = ctrl.second;
> > -                     value.reserve(type, true, info.elems);
> > -                     Span<uint8_t> data = value.data();
> > -
> > -                     v4l2Ctrls[i].p_u8 = data.data();
> > -                     v4l2Ctrls[i].size = data.size();
>
> Is there a need to move this code to the switch ? It looks fairly
> generic, it would be nice not to duplicate it when (if) we latter add
> support for other control types (such as V4L2_CTRL_TYPE_U16).
>
> >               }
> >
> > -             v4l2Ctrls[i].id = id;
> > -             i++;
> > +             v4l2Ctrl.id = id;
> > +             v4l2Ctrls.push_back(std::move(v4l2Ctrl));
>
> The move won't help much, it will copy the v4l2_ext_control instance.
> Should we resize() instead of reserve(), and operate directly on the
> vector entry in this loop ?
>
> >       }
> >
> >       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_G_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 read controls: "
> >                                        << strerror(-ret);
> >                       return {};
> > @@ -250,10 +246,11 @@ ControlList V4L2Device::getControls(const std::vector<uint32_t> &ids)
> >               /* A specific control failed. */
> >               LOG(V4L2, Error) << "Unable to read control " << errorIdx
> >                                << ": " << strerror(-ret);
> > -             count = errorIdx - 1;
> > +
> > +             v4l2Ctrls.resize(errorIdx);
> >       }
> >
> > -     updateControls(&ctrls, v4l2Ctrls, count);
> > +     updateControls(&ctrls, v4l2Ctrls.data(), v4l2Ctrls.size());
>
> updateControls should also take a Span argument, that could be done in
> the same patch that updates the argument to getControls().
>
> Overall this patch is good, the comments above are small issues.
>
> >
> >       return ctrls;
> >  }
> --
> Regards,
>
> Laurent Pinchart