1.. Permission is granted to copy, distribute and/or modify this 2.. document under the terms of the GNU Free Documentation License, 3.. Version 1.1 or any later version published by the Free Software 4.. Foundation, with no Invariant Sections, no Front-Cover Texts 5.. and no Back-Cover Texts. A copy of the license is included at 6.. Documentation/userspace-api/media/fdl-appendix.rst. 7.. 8.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections 9 10.. _VIDIOC_SUBSCRIBE_EVENT: 11.. _VIDIOC_UNSUBSCRIBE_EVENT: 12 13****************************************************** 14ioctl VIDIOC_SUBSCRIBE_EVENT, VIDIOC_UNSUBSCRIBE_EVENT 15****************************************************** 16 17Name 18==== 19 20VIDIOC_SUBSCRIBE_EVENT - VIDIOC_UNSUBSCRIBE_EVENT - Subscribe or unsubscribe event 21 22 23Synopsis 24======== 25 26.. c:function:: int ioctl( int fd, VIDIOC_SUBSCRIBE_EVENT, struct v4l2_event_subscription *argp ) 27 :name: VIDIOC_SUBSCRIBE_EVENT 28 29.. c:function:: int ioctl( int fd, VIDIOC_UNSUBSCRIBE_EVENT, struct v4l2_event_subscription *argp ) 30 :name: VIDIOC_UNSUBSCRIBE_EVENT 31 32 33Arguments 34========= 35 36``fd`` 37 File descriptor returned by :ref:`open() <func-open>`. 38 39``argp`` 40 Pointer to struct :c:type:`v4l2_event_subscription`. 41 42 43Description 44=========== 45 46Subscribe or unsubscribe V4L2 event. Subscribed events are dequeued by 47using the :ref:`VIDIOC_DQEVENT` ioctl. 48 49 50.. tabularcolumns:: |p{4.6cm}|p{4.4cm}|p{8.7cm}| 51 52.. c:type:: v4l2_event_subscription 53 54.. flat-table:: struct v4l2_event_subscription 55 :header-rows: 0 56 :stub-columns: 0 57 :widths: 1 1 2 58 59 * - __u32 60 - ``type`` 61 - Type of the event, see :ref:`event-type`. 62 63 .. note:: 64 65 ``V4L2_EVENT_ALL`` can be used with 66 :ref:`VIDIOC_UNSUBSCRIBE_EVENT <VIDIOC_SUBSCRIBE_EVENT>` for 67 unsubscribing all events at once. 68 * - __u32 69 - ``id`` 70 - ID of the event source. If there is no ID associated with the 71 event source, then set this to 0. Whether or not an event needs an 72 ID depends on the event type. 73 * - __u32 74 - ``flags`` 75 - Event flags, see :ref:`event-flags`. 76 * - __u32 77 - ``reserved``\ [5] 78 - Reserved for future extensions. Drivers and applications must set 79 the array to zero. 80 81 82 83.. tabularcolumns:: |p{6.8cm}|p{2.2cm}|p{8.5cm}| 84 85.. _event-flags: 86 87.. flat-table:: Event Flags 88 :header-rows: 0 89 :stub-columns: 0 90 :widths: 3 1 4 91 92 * - ``V4L2_EVENT_SUB_FL_SEND_INITIAL`` 93 - 0x0001 94 - When this event is subscribed an initial event will be sent 95 containing the current status. This only makes sense for events 96 that are triggered by a status change such as ``V4L2_EVENT_CTRL``. 97 Other events will ignore this flag. 98 * - ``V4L2_EVENT_SUB_FL_ALLOW_FEEDBACK`` 99 - 0x0002 100 - If set, then events directly caused by an ioctl will also be sent 101 to the filehandle that called that ioctl. For example, changing a 102 control using :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` will cause 103 a V4L2_EVENT_CTRL to be sent back to that same filehandle. 104 Normally such events are suppressed to prevent feedback loops 105 where an application changes a control to a one value and then 106 another, and then receives an event telling it that that control 107 has changed to the first value. 108 109 Since it can't tell whether that event was caused by another 110 application or by the :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` 111 call it is hard to decide whether to set the control to the value 112 in the event, or ignore it. 113 114 Think carefully when you set this flag so you won't get into 115 situations like that. 116 117 118Return Value 119============ 120 121On success 0 is returned, on error -1 and the ``errno`` variable is set 122appropriately. The generic error codes are described at the 123:ref:`Generic Error Codes <gen-errors>` chapter. 124