[libcamera-devel] [PATCH v2 5/8] libcamera: v4l2_videodevice: Prevent queueing buffers without a cache

[Kieran Bingham]

Hi Kieran,

On 12/03/2021 05:47, Kieran Bingham wrote:
> The v4l2 buffer cache allows us to map incoming buffers to an instance
> of the V4L2 Buffer required to actually queue.
> 
> If the cache_ is not available, then the buffers required to allow
> queuing to a device have been released, and this indicates an issue at
> the pipeline handler.
> 
> This could be a common mistake, as it could happen if a pipeline handler
> always requeues buffers to the device after they complete, without
> checking if they are cancelled.
> 
> That can then lead to trying to queue a buffer to a device which no
> longer expects buffers, so add a loud message to indicate what has
> happened but return an error without fatally crashing.

Perhaps you forgot to update this commit message.

I'd recommend change the last paragraph to the following when/if committing:

Catch any invalid queueing of buffers to the V4L2 video device when
resources have been released by adding a Fatal log message to highlight
the error during development.

> 
> Signed-off-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> ---
>  src/libcamera/v4l2_videodevice.cpp | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/src/libcamera/v4l2_videodevice.cpp b/src/libcamera/v4l2_videodevice.cpp
> index cb52d4cea3f6..12c09dc7578d 100644
> --- a/src/libcamera/v4l2_videodevice.cpp
> +++ b/src/libcamera/v4l2_videodevice.cpp
> @@ -1391,6 +1391,16 @@ int V4L2VideoDevice::queueBuffer(FrameBuffer *buffer)
>  	struct v4l2_buffer buf = {};
>  	int ret;
>  
> +	/*
> +	 * Pipeline handlers should not requeue buffers after releasing the
> +	 * buffers on the device. Any occurence of this error should be fixed
> +	 * in the pipeline handler directly.
> +	 */
> +	if (!cache_) {
> +		LOG(V4L2, Fatal) << "No BufferCache available to queue.";
> +		return -ENOENT;
> +	}
> +
>  	ret = cache_->get(*buffer);
>  	if (ret < 0)
>  		return ret;
> 

-- 
Regards
--
Kieran