Documentation/userspace-api/media/v4l/vidioc-streamon.rst

Source file repositories/reference/linux-study-clean/Documentation/userspace-api/media/v4l/vidioc-streamon.rst

File Facts

System
Linux kernel
Corpus path
Documentation/userspace-api/media/v4l/vidioc-streamon.rst
Extension
.rst
Size
3403 bytes
Lines
106
Domain
Support Tooling And Documentation
Bucket
Documentation
Inferred role
Support Tooling And Documentation: documentation
Status
atlas-only

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Dependency Surface

Detected Declarations

Annotated Snippet

.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
.. c:namespace:: V4L

.. _VIDIOC_STREAMON:

***************************************
ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF
***************************************

Name
====

VIDIOC_STREAMON - VIDIOC_STREAMOFF - Start or stop streaming I/O

Synopsis
========

.. c:macro:: VIDIOC_STREAMON

``int ioctl(int fd, VIDIOC_STREAMON, const int *argp)``

.. c:macro:: VIDIOC_STREAMOFF

``int ioctl(int fd, VIDIOC_STREAMOFF, const int *argp)``

Arguments
=========

``fd``
    File descriptor returned by :c:func:`open()`.

``argp``
    Pointer to an integer.

Description
===========

The ``VIDIOC_STREAMON`` and ``VIDIOC_STREAMOFF`` ioctl start and stop
the capture or output process during streaming
(:ref:`memory mapping <mmap>`, :ref:`user pointer <userp>` or
:ref:`DMABUF <dmabuf>`) I/O.

Capture hardware is disabled and no input buffers are filled (if there
are any empty buffers in the incoming queue) until ``VIDIOC_STREAMON``
has been called. Output hardware is disabled and no video signal is
produced until ``VIDIOC_STREAMON`` has been called.

Memory-to-memory devices will not start until ``VIDIOC_STREAMON`` has
been called for both the capture and output stream types.

If ``VIDIOC_STREAMON`` fails then any already queued buffers will remain
queued.

The ``VIDIOC_STREAMOFF`` ioctl, apart of aborting or finishing any DMA
in progress, unlocks any user pointer buffers locked in physical memory,
and it removes all buffers from the incoming and outgoing queues. That
means all images captured but not dequeued yet will be lost, likewise
all images enqueued for output but not transmitted yet. I/O returns to
the same state as after calling
:ref:`VIDIOC_REQBUFS` and can be restarted
accordingly.

If buffers have been queued with :ref:`VIDIOC_QBUF` and
``VIDIOC_STREAMOFF`` is called without ever having called
``VIDIOC_STREAMON``, then those queued buffers will also be removed from
the incoming queue and all are returned to the same state as after
calling :ref:`VIDIOC_REQBUFS` and can be restarted
accordingly.

Both ioctls take a pointer to an integer, the desired buffer or stream

Annotation

Implementation Notes