[media] uvcvideo: Implement DMABUF exporter role

Now that videobuf2-vmalloc supports exporting buffers, add support for
the DMABUF exporter role by plugging in the videobuf2 ioctl helper.

Signed-off-by: Laurent Pinchart <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/usb/uvc/uvc_queue.c

···
 	return ret;
 }
 
+int uvc_export_buffer(struct uvc_video_queue *queue,
+		      struct v4l2_exportbuffer *exp)
+{
+	int ret;
+
+	mutex_lock(&queue->mutex);
+	ret = vb2_expbuf(&queue->queue, exp);
+	mutex_unlock(&queue->mutex);
+
+	return ret;
+}
+
 int uvc_dequeue_buffer(struct uvc_video_queue *queue, struct v4l2_buffer *buf,
 		       int nonblocking)
 {

drivers/media/usb/uvc/uvc_v4l2.c

···
 	return uvc_queue_buffer(&stream->queue, buf);
 }
 
+static int uvc_ioctl_expbuf(struct file *file, void *fh,
+			    struct v4l2_exportbuffer *exp)
+{
+	struct uvc_fh *handle = fh;
+	struct uvc_streaming *stream = handle->stream;
+
+	if (!uvc_has_privileges(handle))
+		return -EBUSY;
+
+	return uvc_export_buffer(&stream->queue, exp);
+}
+
 static int uvc_ioctl_dqbuf(struct file *file, void *fh, struct v4l2_buffer *buf)
 {
 	struct uvc_fh *handle = fh;
···
 	.vidioc_reqbufs = uvc_ioctl_reqbufs,
 	.vidioc_querybuf = uvc_ioctl_querybuf,
 	.vidioc_qbuf = uvc_ioctl_qbuf,
+	.vidioc_expbuf = uvc_ioctl_expbuf,
 	.vidioc_dqbuf = uvc_ioctl_dqbuf,
 	.vidioc_create_bufs = uvc_ioctl_create_bufs,
 	.vidioc_streamon = uvc_ioctl_streamon,

drivers/media/usb/uvc/uvcvideo.h

···
 		struct v4l2_create_buffers *v4l2_cb);
 extern int uvc_queue_buffer(struct uvc_video_queue *queue,
 		struct v4l2_buffer *v4l2_buf);
+extern int uvc_export_buffer(struct uvc_video_queue *queue,
+		struct v4l2_exportbuffer *exp);
 extern int uvc_dequeue_buffer(struct uvc_video_queue *queue,
 		struct v4l2_buffer *v4l2_buf, int nonblocking);
 extern int uvc_queue_streamon(struct uvc_video_queue *queue,