85 lines
2 KiB
ReStructuredText
85 lines
2 KiB
ReStructuredText
.. -*- coding: utf-8; mode: rst -*-
|
|
|
|
.. _func-write:
|
|
|
|
************
|
|
V4L2 write()
|
|
************
|
|
|
|
Name
|
|
====
|
|
|
|
v4l2-write - Write to a V4L2 device
|
|
|
|
|
|
Synopsis
|
|
========
|
|
|
|
.. code-block:: c
|
|
|
|
#include <unistd.h>
|
|
|
|
|
|
.. c:function:: ssize_t write( int fd, void *buf, size_t count )
|
|
:name: v4l2-write
|
|
|
|
Arguments
|
|
=========
|
|
|
|
``fd``
|
|
File descriptor returned by :ref:`open() <func-open>`.
|
|
|
|
``buf``
|
|
Buffer with data to be written
|
|
|
|
``count``
|
|
Number of bytes at the buffer
|
|
|
|
Description
|
|
===========
|
|
|
|
:ref:`write() <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, :ref:`write() <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 :ref:`write() <func-write>` function is not supported by this driver,
|
|
not on this device, or generally not on this type of device.
|