OpenCloudOS-Kernel/Documentation/media/uapi/mediactl/request-func-ioctl.rst

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.. _request-func-ioctl:

***************
request ioctl()
***************

Name
====

request-ioctl - Control a request file descriptor


Synopsis
========

.. code-block:: c

    #include <sys/ioctl.h>


.. c:function:: int ioctl( int fd, int cmd, void *argp )
    :name: req-ioctl

Arguments
=========

``fd``
    File descriptor returned by :ref:`MEDIA_IOC_REQUEST_ALLOC`.

``cmd``
    The request ioctl command code as defined in the media.h header file, for
    example :ref:`MEDIA_REQUEST_IOC_QUEUE`.

``argp``
    Pointer to a request-specific structure.


Description
===========

The :ref:`ioctl() <request-func-ioctl>` function manipulates request
parameters. The argument ``fd`` must be an open file descriptor.

The ioctl ``cmd`` code specifies the request function to be called. It
has encoded in it whether the argument is an input, output or read/write
parameter, and the size of the argument ``argp`` in bytes.

Macros and structures definitions specifying request ioctl commands and
their parameters are located in the media.h header file. All request ioctl
commands, their respective function and parameters are specified in
:ref:`media-user-func`.


Return Value
============

On success 0 is returned, on error -1 and the ``errno`` variable is set
appropriately. The generic error codes are described at the
:ref:`Generic Error Codes <gen-errors>` chapter.

Command-specific error codes are listed in the individual command
descriptions.

When an ioctl that takes an output or read/write parameter fails, the
parameter remains unmodified.