[libcamera-devel] [PATCH v2 2/3] libcamera: V4L2Device: Use std::vector for v4l2_ext_control in setControls()

[Laurent Pinchart]

Hi Hiro,

Thank you for the patch.

On Thu, Apr 15, 2021 at 01:48:53PM +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>
> Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> ---
>  src/libcamera/v4l2_device.cpp | 32 +++++++++++++++-----------------
>  1 file changed, 15 insertions(+), 17 deletions(-)
> 
> diff --git a/src/libcamera/v4l2_device.cpp b/src/libcamera/v4l2_device.cpp
> index ee8c3fed..5ec1b10e 100644
> --- a/src/libcamera/v4l2_device.cpp
> +++ b/src/libcamera/v4l2_device.cpp
> @@ -279,12 +279,11 @@ ControlList V4L2Device::getControls(const std::vector<uint32_t> &ids)
>   */
>  int V4L2Device::setControls(ControlList *ctrls)
>  {
> -	unsigned int count = ctrls->size();
> -	if (count == 0)
> +	if (ctrls->empty())
>  		return 0;
>  
> -	struct v4l2_ext_control v4l2Ctrls[count];
> -	memset(v4l2Ctrls, 0, sizeof(v4l2Ctrls));
> +	std::vector<v4l2_ext_control> v4l2Ctrls(ctrls->size());
> +	memset(v4l2Ctrls.data(), 0, v4l2Ctrls.size());

Is the memset() needed ? The std::vector constructor will default-insert
the elements, which value-initializes them. If my interpretation of
https://en.cppreference.com/w/cpp/language/value_initialization is
correct, the elements will be zero-initialized.

>  
>  	unsigned int i = 0;

Should we replace i with

	v4l2_ext_control *v4l2Ctrl = v4l2Ctrls.data();

and do a

	v4l2Ctrl++;

at the end of the loop ? That way we would ensure that i won't be used
incorrectly (after being incremented) inside the loop.

Apart from that,

Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

>  	for (auto &ctrl : *ctrls) {
> @@ -295,14 +294,14 @@ int V4L2Device::setControls(ControlList *ctrls)
>  				<< "Control " << utils::hex(id) << " not found";
>  			return -EINVAL;
>  		}
> -
> -		v4l2Ctrls[i].id = id;
> +		v4l2_ext_control &v4l2Ctrl = v4l2Ctrls[i++];
> +		v4l2Ctrl.id = id;
>  
>  		/* Set the v4l2_ext_control value for the write operation. */
>  		ControlValue &value = ctrl.second;
>  		switch (iter->first->type()) {
>  		case ControlTypeInteger64:
> -			v4l2Ctrls[i].value64 = value.get<int64_t>();
> +			v4l2Ctrl.value64 = value.get<int64_t>();
>  			break;
>  
>  		case ControlTypeByte: {
> @@ -314,32 +313,30 @@ int V4L2Device::setControls(ControlList *ctrls)
>  			}
>  
>  			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();
>  
>  			break;
>  		}
>  
>  		default:
>  			/* \todo To be changed to support strings. */
> -			v4l2Ctrls[i].value = value.get<int32_t>();
> +			v4l2Ctrl.value = value.get<int32_t>();
>  			break;
>  		}
> -
> -		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_S_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 set controls: "
>  					 << strerror(-ret);
>  			return -EINVAL;
> @@ -348,11 +345,12 @@ int V4L2Device::setControls(ControlList *ctrls)
>  		/* A specific control failed. */
>  		LOG(V4L2, Error) << "Unable to set control " << errorIdx
>  				 << ": " << strerror(-ret);
> -		count = errorIdx - 1;
> +
> +		v4l2Ctrls.resize(errorIdx);
>  		ret = errorIdx;
>  	}
>  
> -	updateControls(ctrls, v4l2Ctrls, count);
> +	updateControls(ctrls, v4l2Ctrls.data(), v4l2Ctrls.size());
>  
>  	return ret;
>  }

-- 
Regards,

Laurent Pinchart