mirror of https://gitee.com/openkylin/linux.git
117 lines
3.7 KiB
XML
117 lines
3.7 KiB
XML
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<refentry id="media-func-ioctl">
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<refmeta>
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<refentrytitle>media ioctl()</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>media-ioctl</refname>
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<refpurpose>Control a media device</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <sys/ioctl.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>void *<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Arguments</title>
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<variablelist>
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<varlistentry>
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<term><parameter>fd</parameter></term>
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<listitem>
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<para>&fd;</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>request</parameter></term>
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<listitem>
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<para>Media ioctl request code as defined in the media.h header file,
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for example MEDIA_IOC_SETUP_LINK.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>argp</parameter></term>
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<listitem>
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<para>Pointer to a request-specific structure.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Description</title>
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<para>The <function>ioctl()</function> function manipulates media device
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parameters. The argument <parameter>fd</parameter> must be an open file
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descriptor.</para>
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<para>The ioctl <parameter>request</parameter> code specifies the media
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function to be called. It has encoded in it whether the argument is an
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input, output or read/write parameter, and the size of the argument
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<parameter>argp</parameter> in bytes.</para>
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<para>Macros and structures definitions specifying media ioctl requests and
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their parameters are located in the media.h header file. All media ioctl
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requests, their respective function and parameters are specified in
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<xref linkend="media-user-func" />.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para><function>ioctl()</function> returns <returnvalue>0</returnvalue> on
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success. On failure, <returnvalue>-1</returnvalue> is returned, and the
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<varname>errno</varname> variable is set appropriately. Generic error codes
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are listed below, and request-specific error codes are listed in the
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individual requests descriptions.</para>
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<para>When an ioctl that takes an output or read/write parameter fails,
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the parameter remains unmodified.</para>
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<variablelist>
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<varlistentry>
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<term><errorcode>EBADF</errorcode></term>
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<listitem>
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<para><parameter>fd</parameter> is not a valid open file descriptor.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><errorcode>EFAULT</errorcode></term>
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<listitem>
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<para><parameter>argp</parameter> references an inaccessible memory
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area.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><errorcode>EINVAL</errorcode></term>
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<listitem>
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<para>The <parameter>request</parameter> or the data pointed to by
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<parameter>argp</parameter> is not valid. This is a very common error
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code, see the individual ioctl requests listed in
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<xref linkend="media-user-func" /> for actual causes.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><errorcode>ENOMEM</errorcode></term>
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<listitem>
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<para>Insufficient kernel memory was available to complete the
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request.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><errorcode>ENOTTY</errorcode></term>
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<listitem>
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<para><parameter>fd</parameter> is not associated with a character
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special device.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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</refentry>
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