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+.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
+.. c:namespace:: V4L
+
+.. _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 )
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by :c:func:`open()`.
+
+``buf``
+     Buffer with data to be written
+
+``count``
+    Number of bytes at the buffer
+
+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.