82 lines
2.0 KiB
ReStructuredText
82 lines
2.0 KiB
ReStructuredText
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.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
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.. c:namespace:: V4L
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.. _func-write:
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************
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V4L2 write()
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************
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Name
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====
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v4l2-write - Write to a V4L2 device
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Synopsis
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========
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.. code-block:: c
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#include <unistd.h>
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.. c:function:: ssize_t write( int fd, void *buf, size_t count )
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Arguments
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=========
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``fd``
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File descriptor returned by :c:func:`open()`.
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``buf``
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Buffer with data to be written
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``count``
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Number of bytes at the buffer
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Description
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===========
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:c:func:`write()` writes up to ``count`` bytes to the device
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referenced by the file descriptor ``fd`` from the buffer starting at
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``buf``. When the hardware outputs are not active yet, this function
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enables them. When ``count`` is zero, :c:func:`write()` returns 0
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without any other effect.
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When the application does not provide more data in time, the previous
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video frame, raw VBI image, sliced VPS or WSS data is displayed again.
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Sliced Teletext or Closed Caption data is not repeated, the driver
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inserts a blank line instead.
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Return Value
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============
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On success, the number of bytes written are returned. Zero indicates
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nothing was written. On error, -1 is returned, and the ``errno``
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variable is set appropriately. In this case the next write will start at
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the beginning of a new frame. Possible error codes are:
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EAGAIN
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Non-blocking I/O has been selected using the
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:ref:`O_NONBLOCK <func-open>` flag and no buffer space was
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available to write the data immediately.
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EBADF
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``fd`` is not a valid file descriptor or is not open for writing.
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EBUSY
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The driver does not support multiple write streams and the device is
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already in use.
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EFAULT
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``buf`` references an inaccessible memory area.
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EINTR
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The call was interrupted by a signal before any data was written.
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EIO
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I/O error. This indicates some hardware problem.
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EINVAL
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The :c:func:`write()` function is not supported by this driver,
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not on this device, or generally not on this type of device.
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