147 lines
4.6 KiB
XML
147 lines
4.6 KiB
XML
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<refentry id="func-ioctl">
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<refmeta>
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<refentrytitle>V4L2 ioctl()</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>v4l2-ioctl</refname>
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<refpurpose>Program a V4L2 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>V4L2 ioctl request code as defined in the <link
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linkend="videodev">videodev.h</link> header file, for example
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VIDIOC_QUERYCAP.</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 function parameter, usually a 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 is used to program
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V4L2 devices. The argument <parameter>fd</parameter> must be an open
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file descriptor. An ioctl <parameter>request</parameter> has encoded
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in it whether the argument is an input, output or read/write
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parameter, and the size of the argument <parameter>argp</parameter> in
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bytes. Macros and defines specifying V4L2 ioctl requests are located
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in the <link linkend="videodev">videodev.h</link> header file.
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Applications should use their own copy, not include the version in the
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kernel sources on the system they compile on. All V4L2 ioctl requests,
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their respective function and parameters are specified in <xref
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linkend="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>On success the <function>ioctl()</function> function returns
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<returnvalue>0</returnvalue> and does not reset the
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<varname>errno</varname> variable. On failure
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<returnvalue>-1</returnvalue> is returned, when the ioctl takes an
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output or read/write parameter it remains unmodified, and the
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<varname>errno</varname> variable is set appropriately. See below for
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possible error codes. Generic errors like <errorcode>EBADF</errorcode>
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or <errorcode>EFAULT</errorcode> are not listed in the sections
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discussing individual ioctl requests.</para>
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<para>Note ioctls may return undefined error codes. Since errors
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may have side effects such as a driver reset applications should
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abort on unexpected errors.</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
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descriptor.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><errorcode>EBUSY</errorcode></term>
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<listitem>
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<para>The property cannot be changed right now. Typically
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this error code is returned when I/O is in progress or the driver
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supports multiple opens and another process locked the property.</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
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memory area.</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
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character special device.</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
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to by <parameter>argp</parameter> is not valid. This is a very common
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error code, see the individual ioctl requests listed in <xref
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linkend="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>Not enough physical or virtual memory was available to
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complete the request.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><errorcode>ERANGE</errorcode></term>
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<listitem>
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<para>The application attempted to set a control with the
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&VIDIOC-S-CTRL; ioctl to a value which is out of bounds.</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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<!--
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Local Variables:
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mode: sgml
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sgml-parent-document: "v4l2.sgml"
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indent-tabs-mode: nil
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End:
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-->
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