[libcamera-devel] [PATCH 1/3] libcamera: V4L2Device: Use std::vector for v4l2_ext_control in getControls()
Hirokazu Honda
hiroh at chromium.org
Thu Apr 15 05:42:03 CEST 2021
On Thu, Apr 15, 2021 at 12:10 PM Hirokazu Honda <hiroh at chromium.org> wrote:
>
> 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
> > >>
Sorry, I don't get your suggestion. Can you elaborate?
> > >>
> > >>> }
> > >>>
> > >>> - 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
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