[libcamera-devel] [PATCH v2] v4l2: V4L2CameraProxy: Add support for PREPARE_BUF as one of the supported ioctl

[Laurent Pinchart]

Hi Vedant,

Thank you for the patch.

On Wed, Jan 12, 2022 at 01:41:02AM +0530, Vedant Paranjape wrote:
> Add support for PREPARE_BUF as one of the ioctl. Since this is a compat
> layer, there doesn't seem to be an equivalent to the "transfer ownership
> of the buffer to kernel driver" in V4L2Camera class.
> 
> To match the error checks done by kernel implementation, we'd have to
> check if dmabuf fd is valid and that the buffer size is large enough.
> Doing so will not add any particular value to the program as
> applications most likely don't depend on these conditions being
> handled correctly.
> 
> Signed-off-by: Vedant Paranjape <vedantparanjape160201 at gmail.com>
> Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
>  src/v4l2/v4l2_camera_proxy.cpp | 32 ++++++++++++++++++++++++++++++++
>  src/v4l2/v4l2_camera_proxy.h   |  1 +
>  2 files changed, 33 insertions(+)
> 
> diff --git a/src/v4l2/v4l2_camera_proxy.cpp b/src/v4l2/v4l2_camera_proxy.cpp
> index 4d529bc29a4d..695af5be5c69 100644
> --- a/src/v4l2/v4l2_camera_proxy.cpp
> +++ b/src/v4l2/v4l2_camera_proxy.cpp
> @@ -544,6 +544,37 @@ int V4L2CameraProxy::vidioc_querybuf(V4L2CameraFile *file, struct v4l2_buffer *a
>  	return 0;
>  }
>  
> +int V4L2CameraProxy::vidioc_prepare_buf(V4L2CameraFile *file, struct v4l2_buffer *arg)
> +{
> +	LOG(V4L2Compat, Debug) << "Servicing vidioc_prepare_buf, index = "
> +			       << arg->index << " fd = " << file->efd();

We can replace this with

	LOG(V4L2Compat, Debug)
		<< "[" << file->description() << "] " << __func__
		<< "(index=" << arg->index << ")";

now that the V4L2 compat debugging improvements have been merged.

> +
> +	if (!hasOwnership(file))
> +		return -EBUSY;
> +
> +	if (arg->index >= bufferCount_)
> +		return -EINVAL;
> +
> +	if (arg->flags & V4L2_BUF_FLAG_REQUEST_FD)
> +		return -EINVAL;
> +
> +	if (!validateBufferType(arg->type) ||
> +	    !validateMemoryType(arg->memory))
> +		return -EINVAL;
> +
> +	struct v4l2_buffer &buffer = buffers_[arg->index];
> +
> +	if (buffer.flags & V4L2_BUF_FLAG_QUEUED ||
> +	    buffer.flags & V4L2_BUF_FLAG_PREPARED)
> +		return -EINVAL;
> +
> +	buffer.flags |= V4L2_BUF_FLAG_PREPARED;

This looks good, but there's one missing thing:
V4L2CameraProxy::vidioc_dqbuf() should now clear the
V4L2_BUF_FLAG_PREPARED flag. Can you send a v3 that addresses those two
small issues ?

> +
> +	arg->flags = buffer.flags;
> +
> +	return 0;
> +}
> +
>  int V4L2CameraProxy::vidioc_qbuf(V4L2CameraFile *file, struct v4l2_buffer *arg)
>  {
>  	LOG(V4L2Compat, Debug) << "Servicing vidioc_qbuf, index = "
> @@ -709,6 +740,7 @@ const std::set<unsigned long> V4L2CameraProxy::supportedIoctls_ = {
>  	VIDIOC_S_INPUT,
>  	VIDIOC_REQBUFS,
>  	VIDIOC_QUERYBUF,
> +	VIDIOC_PREPARE_BUF,
>  	VIDIOC_QBUF,
>  	VIDIOC_DQBUF,
>  	VIDIOC_EXPBUF,
> diff --git a/src/v4l2/v4l2_camera_proxy.h b/src/v4l2/v4l2_camera_proxy.h
> index 14e027c3e7d1..6baba94262a9 100644
> --- a/src/v4l2/v4l2_camera_proxy.h
> +++ b/src/v4l2/v4l2_camera_proxy.h
> @@ -57,6 +57,7 @@ private:
>  	int vidioc_s_input(V4L2CameraFile *file, int *arg);
>  	int vidioc_reqbufs(V4L2CameraFile *file, struct v4l2_requestbuffers *arg);
>  	int vidioc_querybuf(V4L2CameraFile *file, struct v4l2_buffer *arg);
> +	int vidioc_prepare_buf(V4L2CameraFile *file, struct v4l2_buffer *arg);
>  	int vidioc_qbuf(V4L2CameraFile *file, struct v4l2_buffer *arg);
>  	int vidioc_dqbuf(V4L2CameraFile *file, struct v4l2_buffer *arg,
>  			 libcamera::Mutex *lock) LIBCAMERA_TSA_REQUIRES(*lock);

-- 
Regards,

Laurent Pinchart