tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
1.. -*- coding: utf-8; mode: rst -*-
2
3.. _func-write:
4
5************
6V4L2 write()
7************
8
9Name
10====
11
12v4l2-write - Write to a V4L2 device
13
14
15Synopsis
16========
17
18.. code-block:: c
19
20 #include <unistd.h>
21
22
23.. cpp:function:: ssize_t write( int fd, void *buf, size_t count )
24
25
26Arguments
27=========
28
29``fd``
30 File descriptor returned by :ref:`open() <func-open>`.
31
32``buf``
33``count``
34
35
36Description
37===========
38
39:ref:`write() <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, :ref:`write() <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
50
51Return Value
52============
53
54On success, the number of bytes written are returned. Zero indicates
55nothing was written. On error, -1 is returned, and the ``errno``
56variable is set appropriately. In this case the next write will start at
57the beginning of a new frame. Possible error codes are:
58
59EAGAIN
60 Non-blocking I/O has been selected using the
61 :ref:`O_NONBLOCK <func-open>` flag and no buffer space was
62 available to write the data immediately.
63
64EBADF
65 ``fd`` is not a valid file descriptor or is not open for writing.
66
67EBUSY
68 The driver does not support multiple write streams and the device is
69 already in use.
70
71EFAULT
72 ``buf`` references an inaccessible memory area.
73
74EINTR
75 The call was interrupted by a signal before any data was written.
76
77EIO
78 I/O error. This indicates some hardware problem.
79
80EINVAL
81 The :ref:`write() <func-write>` function is not supported by this driver,
82 not on this device, or generally not on this type of device.