[libcamera-devel] [PATCH v3] v4l2: V4L2CameraProxy: Add support for PREPARE_BUF as one of the supported ioctl

[paul.elder at ideasonboard.com]

Hi Vedant,

On Wed, Jan 19, 2022 at 11:25:12AM +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.

+ Thus, simply duplicate the checks done by vidioc_qbuf.

, perhaps? You describe a (minor) issue but no solution.

> 
> 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.

Would we add these once we support importing buffers, just for
correctness?

> 
> Signed-off-by: Vedant Paranjape <vedantparanjape160201 at gmail.com>
> Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
>  src/v4l2/v4l2_camera_proxy.cpp | 35 +++++++++++++++++++++++++++++++++-
>  src/v4l2/v4l2_camera_proxy.h   |  1 +
>  2 files changed, 35 insertions(+), 1 deletion(-)
> 
> diff --git a/src/v4l2/v4l2_camera_proxy.cpp b/src/v4l2/v4l2_camera_proxy.cpp
> index ec6daac605fb..f3470a6d312a 100644
> --- a/src/v4l2/v4l2_camera_proxy.cpp
> +++ b/src/v4l2/v4l2_camera_proxy.cpp
> @@ -559,6 +559,38 @@ 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)
> +		<< "[" << file->description() << "] " << __func__
> +		<< "(index=" << arg->index << ")";
> +
> +	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;

I would've said that these checks should be in the same order as in
qbuf, but I guess you've copied this order from the kernel. In which
case qbuf should be fixed (in a separate patch; this one's fine).

> +
> +	struct v4l2_buffer &buffer = buffers_[arg->index];
> +
> +	if (buffer.flags & V4L2_BUF_FLAG_QUEUED ||
> +	    buffer.flags & V4L2_BUF_FLAG_PREPARED)
> +		return -EINVAL;

Huh, I didn't realize that preparing a buf that's already been prepared
would be an error. I thought you could just nop it. v4l2 docs haven't
kept up I suppose :/

I would say that we could check the prepared flag in qbuf too, but these
checks are few and constant time so it's probably find as-is.


Looks good.

With or without the suggested changes,

Reviewed-by: Paul Elder <paul.elder at ideasonboard.com>

> +
> +	buffer.flags |= V4L2_BUF_FLAG_PREPARED;
> +
> +	arg->flags = buffer.flags;
> +
> +	return 0;
> +}
> +
>  int V4L2CameraProxy::vidioc_qbuf(V4L2CameraFile *file, struct v4l2_buffer *arg)
>  {
>  	LOG(V4L2Compat, Debug)
> @@ -627,7 +659,7 @@ int V4L2CameraProxy::vidioc_dqbuf(V4L2CameraFile *file, struct v4l2_buffer *arg,
>  
>  	struct v4l2_buffer &buf = buffers_[currentBuf_];
>  
> -	buf.flags &= ~(V4L2_BUF_FLAG_QUEUED | V4L2_BUF_FLAG_DONE);
> +	buf.flags &= ~(V4L2_BUF_FLAG_QUEUED | V4L2_BUF_FLAG_DONE | V4L2_BUF_FLAG_PREPARED);
>  	buf.length = sizeimage_;
>  	*arg = buf;
>  
> @@ -729,6 +761,7 @@ 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 a38b28c744d3..76ca2d8a5558 100644
> --- a/src/v4l2/v4l2_camera_proxy.h
> +++ b/src/v4l2/v4l2_camera_proxy.h
> @@ -58,6 +58,7 @@ 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);
> -- 
> 2.25.1
>