[libcamera-devel] [PATCH v6 1/3] libcamera: V4L2Device: Replace VLA with std::vector in getControls()

[Hirokazu Honda]

Hi Laurent, thanks for the patch.
After all, I am fine with this.
We may want to improve the code a bit by using utils::enumerate(). I
will review your patch series today.

On Mon, Apr 26, 2021 at 9:12 AM Laurent Pinchart
<laurent.pinchart at ideasonboard.com> wrote:
>
> From: Hirokazu Honda <hiroh at chromium.org>
>
> 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>
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
>  src/libcamera/v4l2_device.cpp | 28 ++++++++++++++--------------
>  1 file changed, 14 insertions(+), 14 deletions(-)
>
> diff --git a/src/libcamera/v4l2_device.cpp b/src/libcamera/v4l2_device.cpp
> index decd19ef5281..3a4df4f6c098 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)
>  {
> -       unsigned int count = ids.size();
> -       if (count == 0)
> +       if (ids.empty())
>                 return {};
>
>         ControlList ctrls{ controls_ };
> @@ -196,14 +195,17 @@ ControlList V4L2Device::getControls(const std::vector<uint32_t> &ids)
>                 ctrls.set(id, {});
>         }
>
> -       struct v4l2_ext_control v4l2Ctrls[count];
> -       memset(v4l2Ctrls, 0, sizeof(v4l2Ctrls));
> +       std::vector<v4l2_ext_control> v4l2Ctrls(ids.size());

I missed this upon reviewing. v4l2Ctrls(ctrls.size()) is better.

-Hiro

> +       memset(v4l2Ctrls.data(), 0, sizeof(v4l2_ext_control) * ctrls.size());
>
>         unsigned int i = 0;
>         for (auto &ctrl : ctrls) {
>                 unsigned int id = ctrl.first;
>                 const struct v4l2_query_ext_ctrl &info = controlInfo_[id];
>
> +               v4l2_ext_control &v4l2Ctrl = v4l2Ctrls[i++];
> +               v4l2Ctrl.id = id;
> +
>                 if (info.flags & V4L2_CTRL_FLAG_HAS_PAYLOAD) {
>                         ControlType type;
>
> @@ -223,25 +225,22 @@ ControlList V4L2Device::getControls(const std::vector<uint32_t> &ids)
>                         value.reserve(type, true, info.elems);
>                         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();
>                 }
> -
> -               v4l2Ctrls[i].id = id;
> -               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_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 +249,11 @@ 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());
>
>         return ctrls;
>  }
> --
> Regards,
>
> Laurent Pinchart
>