1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2.. c:namespace:: V4L 3 4.. _VIDIOC_STREAMON: 5 6*************************************** 7ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF 8*************************************** 9 10Name 11==== 12 13VIDIOC_STREAMON - VIDIOC_STREAMOFF - Start or stop streaming I/O 14 15Synopsis 16======== 17 18.. c:macro:: VIDIOC_STREAMON 19 20``int ioctl(int fd, VIDIOC_STREAMON, const int *argp)`` 21 22.. c:macro:: VIDIOC_STREAMOFF 23 24``int ioctl(int fd, VIDIOC_STREAMOFF, const int *argp)`` 25 26Arguments 27========= 28 29``fd`` 30 File descriptor returned by :c:func:`open()`. 31 32``argp`` 33 Pointer to an integer. 34 35Description 36=========== 37 38The ``VIDIOC_STREAMON`` and ``VIDIOC_STREAMOFF`` ioctl start and stop 39the capture or output process during streaming 40(:ref:`memory mapping <mmap>`, :ref:`user pointer <userp>` or 41:ref:`DMABUF <dmabuf>`) I/O. 42 43Capture hardware is disabled and no input buffers are filled (if there 44are any empty buffers in the incoming queue) until ``VIDIOC_STREAMON`` 45has been called. Output hardware is disabled and no video signal is 46produced until ``VIDIOC_STREAMON`` has been called. 47 48Memory-to-memory devices will not start until ``VIDIOC_STREAMON`` has 49been called for both the capture and output stream types. 50 51If ``VIDIOC_STREAMON`` fails then any already queued buffers will remain 52queued. 53 54The ``VIDIOC_STREAMOFF`` ioctl, apart of aborting or finishing any DMA 55in progress, unlocks any user pointer buffers locked in physical memory, 56and it removes all buffers from the incoming and outgoing queues. That 57means all images captured but not dequeued yet will be lost, likewise 58all images enqueued for output but not transmitted yet. I/O returns to 59the same state as after calling 60:ref:`VIDIOC_REQBUFS` and can be restarted 61accordingly. 62 63If buffers have been queued with :ref:`VIDIOC_QBUF` and 64``VIDIOC_STREAMOFF`` is called without ever having called 65``VIDIOC_STREAMON``, then those queued buffers will also be removed from 66the incoming queue and all are returned to the same state as after 67calling :ref:`VIDIOC_REQBUFS` and can be restarted 68accordingly. 69 70Both ioctls take a pointer to an integer, the desired buffer or stream 71type. This is the same as struct 72:c:type:`v4l2_requestbuffers` ``type``. 73 74If ``VIDIOC_STREAMON`` is called when streaming is already in progress, 75or if ``VIDIOC_STREAMOFF`` is called when streaming is already stopped, 76then 0 is returned. Nothing happens in the case of ``VIDIOC_STREAMON``, 77but ``VIDIOC_STREAMOFF`` will return queued buffers to their starting 78state as mentioned above. 79 80.. note:: 81 82 Applications can be preempted for unknown periods right before 83 or after the ``VIDIOC_STREAMON`` or ``VIDIOC_STREAMOFF`` calls, there is 84 no notion of starting or stopping "now". Buffer timestamps can be used 85 to synchronize with other events. 86 87Return Value 88============ 89 90On success 0 is returned, on error -1 and the ``errno`` variable is set 91appropriately. The generic error codes are described at the 92:ref:`Generic Error Codes <gen-errors>` chapter. 93 94EINVAL 95 The buffer ``type`` is not supported, or no buffers have been 96 allocated (memory mapping) or enqueued (output) yet. 97 98EPIPE 99 The driver implements 100 :ref:`pad-level format configuration <pad-level-formats>` and the 101 pipeline configuration is invalid. 102 103ENOLINK 104 The driver implements Media Controller interface and the pipeline 105 link configuration is invalid. 106