The V4L2 compatibility layer keeps track of the index of the next buffer to be dequeued, to handle VIDIOC_DQBUF. This index is set to 0 on startup and incremented (modulo #frames), and is otherwise never reset. This means that if the last handled frame index is not #frames-1, and the stream is restarted without restarting libcamera and the V4L2 compatilibity layer, the buffer index number won't match with the libcamera buffer index number, causing a segfault. Fix this by resetting the current buffer index to zero on VIDIOC_STREAMON. Signed-off-by: Paul Elder <paul.elder@ideasonboard.com> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>