1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2.. c:namespace:: V4L
3
4.. _func-write:
5
6************
7V4L2 write()
8************
9
10Name
11====
12
13v4l2-write - Write to a V4L2 device
14
15Synopsis
16========
17
18.. code-block:: c
19
20    #include <unistd.h>
21
22.. c:function:: ssize_t write( int fd, void *buf, size_t count )
23
24Arguments
25=========
26
27``fd``
28    File descriptor returned by :c:func:`open()`.
29
30``buf``
31     Buffer with data to be written
32
33``count``
34    Number of bytes at the buffer
35
36Description
37===========
38
39:c:func:`write()` writes up to ``count`` bytes to the device
40referenced by the file descriptor ``fd`` from the buffer starting at
41``buf``. When the hardware outputs are not active yet, this function
42enables them. When ``count`` is zero, :c:func:`write()` returns 0
43without any other effect.
44
45When the application does not provide more data in time, the previous
46video frame, raw VBI image, sliced VPS or WSS data is displayed again.
47Sliced Teletext or Closed Caption data is not repeated, the driver
48inserts a blank line instead.
49
50Return Value
51============
52
53On success, the number of bytes written are returned. Zero indicates
54nothing was written. On error, -1 is returned, and the ``errno``
55variable is set appropriately. In this case the next write will start at
56the beginning of a new frame. Possible error codes are:
57
58EAGAIN
59    Non-blocking I/O has been selected using the
60    :ref:`O_NONBLOCK <func-open>` flag and no buffer space was
61    available to write the data immediately.
62
63EBADF
64    ``fd`` is not a valid file descriptor or is not open for writing.
65
66EBUSY
67    The driver does not support multiple write streams and the device is
68    already in use.
69
70EFAULT
71    ``buf`` references an inaccessible memory area.
72
73EINTR
74    The call was interrupted by a signal before any data was written.
75
76EIO
77    I/O error. This indicates some hardware problem.
78
79EINVAL
80    The :c:func:`write()` function is not supported by this driver,
81    not on this device, or generally not on this type of device.
82