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

[Hirokazu Honda]

On Wed, Apr 14, 2021 at 5:17 PM Kieran Bingham
<kieran.bingham at ideasonboard.com> wrote:
>
> Hi Hiro,
>
> On 14/04/2021 02:45, Hirokazu Honda wrote:
> > Hi Kieran,
> >
> > On Wed, Apr 14, 2021 at 6:58 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.
> >>>
> >>> Signed-off-by: Hirokazu Honda <hiroh at chromium.org>
> >>> ---
> >>>  src/libcamera/v4l2_device.cpp | 44 +++++++++++++++++------------------
> >>>  1 file changed, 21 insertions(+), 23 deletions(-)
> >>>
> >>> diff --git a/src/libcamera/v4l2_device.cpp b/src/libcamera/v4l2_device.cpp
> >>> index decd19ef..78c289c2 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_ };
> >>> @@ -196,21 +195,26 @@ 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());
> >>
> >> The v4l2ctrls array is created of size count which was ids.size();
> >> Shouldn't we reserve this as ids.size() here instead of ctrls.size()?
> >>
> >
> > Yeah, I am also confused by the point upon creating this patch.
> > The original implementation seems to contain a bug;
> > count = id.size() and v4l2Ctrls's size is count, but the iteration is
> > up to ctrls.size() and thus v4l2Ctrls[ctrls.size() - 1] is set.
> > I expect this is out-of-bounds bug.
> > This patch fixes it by setting v4l2Ctrls.size() to ctrls.size() and
> > keeping the original return semantics.
> > However, I still don't get the original return semantics is correct.
> > The doc states "This method reads the value of all controls contained
> > in \a ids, and returns their values as a ControlList."
> > The implementation looks to return all the control values regardless of ids.
> > +Laurent Pinchart do you have any idea?
>
> I think this is where it's important to keep distinct changes in
> separate patches.
>
> Try to make this patch perform only the conversion to the vector, with
> like-for-like (bugz inclusive) functionality, and then it's easier to
> discuss and fix the bug if it is there directly in it's own patch.
>

I got it. The bug fix is much simpler than I thought.
I submitted as an independent patch and will rebase this patch series
on top of it.

Thanks,
-Hiro
> >
> >>
> >>>       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));
> >>
> >> Can v4l2Ctrl initialisation be simplified to this?:
> >>         v4l2_ext_control v4l2Ctrl = {};
> >>
> >>>
> >>>               if (info.flags & V4L2_CTRL_FLAG_HAS_PAYLOAD) {
> >>> -                     ControlType type;
> >>> -
> >>>                       switch (info.type) {
> >>> -                     case V4L2_CTRL_TYPE_U8:
> >>> +                     case V4L2_CTRL_TYPE_U8: {
> >>> +                             ControlType type;
> >>>                               type = ControlTypeByte;
> >>> +                             ControlValue &value = ctrl.second;
> >>> +                             value.reserve(type, true, info.elems);
> >>
> >> Is this the only usage of type? Couldn't we just do
> >>  value.reserve(ControlTypeByte, true, info.elems);
> >>
> >> Or at the least make it
> >>
> >> ControlType = ControlTypeByte;
> >>
> >> rather than use an extra line.
> >>
> >>
> >>> +                             Span<uint8_t> data = value.data();
> >>> +                             v4l2Ctrl.p_u8 = data.data();
> >>> +                             v4l2Ctrl.size = data.size();
> >>>                               break;
> >>> +                     }
> >>>
> >>>                       default:
> >>>                               LOG(V4L2, Error)
> >>> @@ -218,30 +222,23 @@ ControlList V4L2Device::getControls(const std::vector<uint32_t> &ids)
> >>>                                       << info.type;
> >>>                               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();
> >>
> >> That switch statement must have been arranged like that to facilitate
> >> easily adding other types later.
> >>
> >> If we don't need to do that, can we fix this up to lower the indentation
> >> somehow? We're four levels in here in places :-S
> >>
> >>
> >>>               }
> >>>
> >>> -             v4l2Ctrls[i].id = id;
> >>> -             i++;
> >>> +             v4l2Ctrl.id = id;
> >>> +             v4l2Ctrls.push_back(std::move(v4l2Ctrl));
> >>>       }
> >>>
> >>>       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 +247,11 @@ 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());
> >>
> >> I was going to say can we pass v4l2Ctrls directly, but now I've seen
> >> your later patch ;=)
> >>
> >>
> >>
> >>>
> >>>       return ctrls;
> >>>  }
> >>>
> >>
> >> --
> >> Regards
> >> --
> >> Kieran
>
> --
> Regards
> --
> Kieran