ioctl VIDIOC_SUBSCRIBE_EVENT, VIDIOC_UNSUBSCRIBE_EVENT &manvol; VIDIOC_SUBSCRIBE_EVENT VIDIOC_UNSUBSCRIBE_EVENT Subscribe or unsubscribe event int ioctl int fd int request struct v4l2_event_subscription *argp fd &fd; request VIDIOC_SUBSCRIBE_EVENT, VIDIOC_UNSUBSCRIBE_EVENT argp Subscribe or unsubscribe V4L2 event. Subscribed events are dequeued by using the &VIDIOC-DQEVENT; ioctl. &cs-str; __u32 type Type of the event, see . Note that V4L2_EVENT_ALL can be used with VIDIOC_UNSUBSCRIBE_EVENT for unsubscribing all events at once. __u32 id ID of the event source. If there is no ID associated with the event source, then set this to 0. Whether or not an event needs an ID depends on the event type. __u32 flags Event flags, see . __u32 reserved[5] Reserved for future extensions. Drivers and applications must set the array to zero. &cs-def; V4L2_EVENT_SUB_FL_SEND_INITIAL 0x0001 When this event is subscribed an initial event will be sent containing the current status. This only makes sense for events that are triggered by a status change such as V4L2_EVENT_CTRL. Other events will ignore this flag. V4L2_EVENT_SUB_FL_ALLOW_FEEDBACK 0x0002 If set, then events directly caused by an ioctl will also be sent to the filehandle that called that ioctl. For example, changing a control using &VIDIOC-S-CTRL; will cause a V4L2_EVENT_CTRL to be sent back to that same filehandle. Normally such events are suppressed to prevent feedback loops where an application changes a control to a one value and then another, and then receives an event telling it that that control has changed to the first value. Since it can't tell whether that event was caused by another application or by the &VIDIOC-S-CTRL; call it is hard to decide whether to set the control to the value in the event, or ignore it. Think carefully when you set this flag so you won't get into situations like that. &return-value;