0001 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
0002 .. c:namespace:: V4L
0003
0004 .. _func-write:
0005
0006 ************
0007 V4L2 write()
0008 ************
0009
0010 Name
0011 ====
0012
0013 v4l2-write - Write to a V4L2 device
0014
0015 Synopsis
0016 ========
0017
0018 .. code-block:: c
0019
0020 #include <unistd.h>
0021
0022 .. c:function:: ssize_t write( int fd, void *buf, size_t count )
0023
0024 Arguments
0025 =========
0026
0027 ``fd``
0028 File descriptor returned by :c:func:`open()`.
0029
0030 ``buf``
0031 Buffer with data to be written
0032
0033 ``count``
0034 Number of bytes at the buffer
0035
0036 Description
0037 ===========
0038
0039 :c:func:`write()` writes up to ``count`` bytes to the device
0040 referenced by the file descriptor ``fd`` from the buffer starting at
0041 ``buf``. When the hardware outputs are not active yet, this function
0042 enables them. When ``count`` is zero, :c:func:`write()` returns 0
0043 without any other effect.
0044
0045 When the application does not provide more data in time, the previous
0046 video frame, raw VBI image, sliced VPS or WSS data is displayed again.
0047 Sliced Teletext or Closed Caption data is not repeated, the driver
0048 inserts a blank line instead.
0049
0050 Return Value
0051 ============
0052
0053 On success, the number of bytes written are returned. Zero indicates
0054 nothing was written. On error, -1 is returned, and the ``errno``
0055 variable is set appropriately. In this case the next write will start at
0056 the beginning of a new frame. Possible error codes are:
0057
0058 EAGAIN
0059 Non-blocking I/O has been selected using the
0060 :ref:`O_NONBLOCK <func-open>` flag and no buffer space was
0061 available to write the data immediately.
0062
0063 EBADF
0064 ``fd`` is not a valid file descriptor or is not open for writing.
0065
0066 EBUSY
0067 The driver does not support multiple write streams and the device is
0068 already in use.
0069
0070 EFAULT
0071 ``buf`` references an inaccessible memory area.
0072
0073 EINTR
0074 The call was interrupted by a signal before any data was written.
0075
0076 EIO
0077 I/O error. This indicates some hardware problem.
0078
0079 EINVAL
0080 The :c:func:`write()` function is not supported by this driver,
0081 not on this device, or generally not on this type of device.
