On Wed, 29 Apr 2009, [UTF-8] Németh Márton wrote:
> The parameter of VIDIOC_REQBUFS is a pointer to struct v4l2_requestbuffers.
> This structure has reserved fields which has to be filled with zeros
> according to the V4L2 API specification, revision 0.24 [1].

As I read the spec, the reserved fields can be used for input from user
space if the buffer is of type V4L2_BUF_TYPE_PRIVATE or higher.