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

[Kieran Bingham]

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.
> ---
>  src/libcamera/v4l2_device.cpp | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/src/libcamera/v4l2_device.cpp b/src/libcamera/v4l2_device.cpp
> index 78c289c2..8625dde8 100644
> --- a/src/libcamera/v4l2_device.cpp
> +++ b/src/libcamera/v4l2_device.cpp
> @@ -280,12 +280,11 @@ 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());

Does the vector not initialise in anyway ?

Looking at https://www.cplusplus.com/reference/vector/vector/vector/
this must be using the fill(2) constructor.

I suspect if nothing is provided, it won't fill, so perhaps it's not
initialised, but if that's the case, I wonder if the right way to
construct this is more like:

	std::vector<v4l2_ext_control> v4l2Ctrls(ctrls->size(), {});

But I'm not particular certain.

Otherwise, this looks Ok to me...

Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>

>  
>  	unsigned int i = 0;
>  	for (auto &ctrl : *ctrls) {
> @@ -332,15 +331,15 @@ int V4L2Device::setControls(ControlList *ctrls)
>  
>  	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;
> @@ -349,11 +348,12 @@ 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
--
Kieran