v4l2: v4l2_camera_proxy: Don't allow buffers to be freed if still mmaped

In VIDIOC_REQBUFS with count = 0, if the buffers are still mmaped, they
should not be allowed to be freed. Add a check for this.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/v4l2/v4l2_camera_proxy.cpp

@@ -470,6 +470,10 @@ int V4L2CameraProxy::vidioc_reqbufs(V4L2CameraFile *file, struct v4l2_requestbuf
 	memset(arg->reserved, 0, sizeof(arg->reserved));
 
 	if (arg->count == 0) {
+		/* \todo Add buffer orphaning support */
+		if (!mmaps_.empty())
+			return -EBUSY;
+
 		if (vcam_->isRunning())
 			return -EBUSY;