[deliverable/linux.git] / Documentation / linux_tv / media / v4l / func-write.rst

.. -*- coding: utf-8; mode: rst -*-

.. _func-write:

************
V4L2 write()
************

*man v4l2-write(2)*

Write to a V4L2 device


Synopsis
========

.. code-block:: c

    #include <unistd.h>


.. cpp:function:: ssize_t write( int fd, void *buf, size_t count )

Arguments
=========

``fd``
    File descriptor returned by :ref:`open() <func-open>`.

``buf``
``count``


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

:c:func:`write()` writes up to ``count`` bytes to the device
referenced by the file descriptor ``fd`` from the buffer starting at
``buf``. When the hardware outputs are not active yet, this function
enables them. When ``count`` is zero, :c:func:`write()` returns 0
without any other effect.

When the application does not provide more data in time, the previous
video frame, raw VBI image, sliced VPS or WSS data is displayed again.
Sliced Teletext or Closed Caption data is not repeated, the driver
inserts a blank line instead.


Return Value
============

On success, the number of bytes written are returned. Zero indicates
nothing was written. On error, -1 is returned, and the ``errno``
variable is set appropriately. In this case the next write will start at
the beginning of a new frame. Possible error codes are:

EAGAIN
    Non-blocking I/O has been selected using the
    :ref:`O_NONBLOCK <func-open>` flag and no buffer space was
    available to write the data immediately.

EBADF
    ``fd`` is not a valid file descriptor or is not open for writing.

EBUSY
    The driver does not support multiple write streams and the device is
    already in use.

EFAULT
    ``buf`` references an inaccessible memory area.

EINTR
    The call was interrupted by a signal before any data was written.

EIO
    I/O error. This indicates some hardware problem.

EINVAL
    The :c:func:`write()` function is not supported by this driver,
    not on this device, or generally not on this type of device.


.. ------------------------------------------------------------------------------
.. This file was automatically converted from DocBook-XML with the dbxml
.. library (https://github.com/return42/sphkerneldoc). The origin XML comes
.. from the linux kernel, refer to:
..
.. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook
.. ------------------------------------------------------------------------------
Commit	Line	Data
5377d91f MH	1	.. -- coding: utf-8; mode: rst --
	2
	3	.. _func-write:
	4
	5	************
	6	V4L2 write()
	7	************
	8
	9	man v4l2-write(2)
	10
	11	Write to a V4L2 device
	12
	13
	14	Synopsis
	15	========
	16
	17	.. code-block:: c
	18
	19	#include <unistd.h>
	20
	21
b7e67f6c	22	.. cpp:function:: ssize_t write( int fd, void *buf, size_t count )
5377d91f MH	23
	24	Arguments
	25	=========
	26
	27	``fd``
	28	File descriptor returned by :ref:`open() <func-open>`.
	29
	30	``buf``
	31	``count``
	32
	33
	34	Description
	35	===========
	36
	37	:c:func:`write()` writes up to ``count`` bytes to the device
	38	referenced by the file descriptor ``fd`` from the buffer starting at
	39	``buf``. When the hardware outputs are not active yet, this function
	40	enables them. When ``count`` is zero, :c:func:`write()` returns 0
	41	without any other effect.
	42
	43	When the application does not provide more data in time, the previous
	44	video frame, raw VBI image, sliced VPS or WSS data is displayed again.
	45	Sliced Teletext or Closed Caption data is not repeated, the driver
	46	inserts a blank line instead.
	47
	48
	49	Return Value
	50	============
	51
	52	On success, the number of bytes written are returned. Zero indicates
	53	nothing was written. On error, -1 is returned, and the ``errno``
	54	variable is set appropriately. In this case the next write will start at
	55	the beginning of a new frame. Possible error codes are:
	56
	57	EAGAIN
	58	Non-blocking I/O has been selected using the
	59	:ref:`O_NONBLOCK <func-open>` flag and no buffer space was
	60	available to write the data immediately.
	61
	62	EBADF
	63	``fd`` is not a valid file descriptor or is not open for writing.
	64
	65	EBUSY
	66	The driver does not support multiple write streams and the device is
	67	already in use.
	68
	69	EFAULT
	70	``buf`` references an inaccessible memory area.
	71
	72	EINTR
	73	The call was interrupted by a signal before any data was written.
	74
	75	EIO
	76	I/O error. This indicates some hardware problem.
	77
	78	EINVAL
	79	The :c:func:`write()` function is not supported by this driver,
	80	not on this device, or generally not on this type of device.
	81
	82
	83	.. ------------------------------------------------------------------------------
	84	.. This file was automatically converted from DocBook-XML with the dbxml
	85	.. library (https://github.com/return42/sphkerneldoc). The origin XML comes
	86	.. from the linux kernel, refer to:
87	..
88	.. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook
89	.. ------------------------------------------------------------------------------