.. -*- coding: utf-8; mode: rst -*-
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.. _VIDIOC_PREPARE_BUF:
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************************
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ioctl VIDIOC_PREPARE_BUF
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************************
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Name
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====
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VIDIOC_PREPARE_BUF - Prepare a buffer for I/O
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Synopsis
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========
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.. c:function:: int ioctl( int fd, VIDIOC_PREPARE_BUF, struct v4l2_buffer *argp )
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:name: VIDIOC_PREPARE_BUF
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Arguments
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=========
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``fd``
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File descriptor returned by :ref:`open() <func-open>`.
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``argp``
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Pointer to struct :c:type:`v4l2_buffer`.
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Description
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===========
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Applications can optionally call the :ref:`VIDIOC_PREPARE_BUF` ioctl to
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pass ownership of the buffer to the driver before actually enqueuing it,
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using the :ref:`VIDIOC_QBUF <VIDIOC_QBUF>` ioctl, and to prepare it for future I/O. Such
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preparations may include cache invalidation or cleaning. Performing them
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in advance saves time during the actual I/O. In case such cache
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operations are not required, the application can use one of
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``V4L2_BUF_FLAG_NO_CACHE_INVALIDATE`` and
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``V4L2_BUF_FLAG_NO_CACHE_CLEAN`` flags to skip the respective step.
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The struct :c:type:`v4l2_buffer` structure is specified in
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:ref:`buffer`.
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Return Value
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============
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On success 0 is returned, on error -1 and the ``errno`` variable is set
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appropriately. The generic error codes are described at the
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:ref:`Generic Error Codes <gen-errors>` chapter.
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EBUSY
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File I/O is in progress.
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EINVAL
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The buffer ``type`` is not supported, or the ``index`` is out of
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bounds, or no buffers have been allocated yet, or the ``userptr`` or
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``length`` are invalid.
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