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

[Laurent Pinchart]

Hi Hiro,

On Tue, Apr 27, 2021 at 10:23:44AM +0900, Hirokazu Honda wrote:
> 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 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.

I've also noticed that after merging the patch :-( I'll send a fix.

> > +       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