1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2 3.. _VIDIOC_STREAMON: 4 5*************************************** 6ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF 7*************************************** 8 9Name 10==== 11 12VIDIOC_STREAMON - VIDIOC_STREAMOFF - Start or stop streaming I/O 13 14 15Synopsis 16======== 17 18.. c:function:: int ioctl( int fd, VIDIOC_STREAMON, const int *argp ) 19 :name: VIDIOC_STREAMON 20 21.. c:function:: int ioctl( int fd, VIDIOC_STREAMOFF, const int *argp ) 22 :name: VIDIOC_STREAMOFF 23 24 25Arguments 26========= 27 28``fd`` 29 File descriptor returned by :ref:`open() <func-open>`. 30 31``argp`` 32 Pointer to an integer. 33 34Description 35=========== 36 37The ``VIDIOC_STREAMON`` and ``VIDIOC_STREAMOFF`` ioctl start and stop 38the capture or output process during streaming 39(:ref:`memory mapping <mmap>`, :ref:`user pointer <userp>` or 40:ref:`DMABUF <dmabuf>`) I/O. 41 42Capture hardware is disabled and no input buffers are filled (if there 43are any empty buffers in the incoming queue) until ``VIDIOC_STREAMON`` 44has been called. Output hardware is disabled and no video signal is 45produced until ``VIDIOC_STREAMON`` has been called. The ioctl will 46succeed when at least one output buffer is in the incoming queue. 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 87 88Return Value 89============ 90 91On success 0 is returned, on error -1 and the ``errno`` variable is set 92appropriately. The generic error codes are described at the 93:ref:`Generic Error Codes <gen-errors>` chapter. 94 95EINVAL 96 The buffer ``type`` is not supported, or no buffers have been 97 allocated (memory mapping) or enqueued (output) yet. 98 99EPIPE 100 The driver implements 101 :ref:`pad-level format configuration <pad-level-formats>` and the 102 pipeline configuration is invalid. 103 104ENOLINK 105 The driver implements Media Controller interface and the pipeline 106 link configuration is invalid. 107