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<refentry id="vidioc-g-ctrl">
<refmeta>
<refentrytitle>ioctl VIDIOC_G_CTRL, VIDIOC_S_CTRL</refentrytitle>
&manvol;
</refmeta>
<refnamediv>
<refname>VIDIOC_G_CTRL</refname>
<refname>VIDIOC_S_CTRL</refname>
<refpurpose>Get or set the value of a control</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcprototype>
<funcdef>int <function>ioctl</function></funcdef>
<paramdef>int <parameter>fd</parameter></paramdef>
<paramdef>int <parameter>request</parameter></paramdef>
<paramdef>struct v4l2_control
*<parameter>argp</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Arguments</title>
<variablelist>
<varlistentry>
<term><parameter>fd</parameter></term>
<listitem>
<para>&fd;</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>request</parameter></term>
<listitem>
<para>VIDIOC_G_CTRL, VIDIOC_S_CTRL</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>argp</parameter></term>
<listitem>
<para></para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Description</title>
<para>To get the current value of a control applications
initialize the <structfield>id</structfield> field of a struct
<structname>v4l2_control</structname> and call the
<constant>VIDIOC_G_CTRL</constant> ioctl with a pointer to this
structure. To change the value of a control applications initialize
the <structfield>id</structfield> and <structfield>value</structfield>
fields of a struct <structname>v4l2_control</structname> and call the
<constant>VIDIOC_S_CTRL</constant> ioctl.</para>
<para>When the <structfield>id</structfield> is invalid drivers
return an &EINVAL;. When the <structfield>value</structfield> is out
of bounds drivers can choose to take the closest valid value or return
an &ERANGE;, whatever seems more appropriate. However,
<constant>VIDIOC_S_CTRL</constant> is a write-only ioctl, it does not
return the actual new value. If the <structfield>value</structfield>
is inappropriate for the control (e.g. if it refers to an unsupported
menu index of a menu control), then &EINVAL; is returned as well.</para>
<para>These ioctls work only with user controls. For other
control classes the &VIDIOC-G-EXT-CTRLS;, &VIDIOC-S-EXT-CTRLS; or
&VIDIOC-TRY-EXT-CTRLS; must be used.</para>
<table pgwide="1" frame="none" id="v4l2-control">
<title>struct <structname>v4l2_control</structname></title>
<tgroup cols="3">
&cs-str;
<tbody valign="top">
<row>
<entry>__u32</entry>
<entry><structfield>id</structfield></entry>
<entry>Identifies the control, set by the
application.</entry>
</row>
<row>
<entry>__s32</entry>
<entry><structfield>value</structfield></entry>
<entry>New value or current value.</entry>
</row>
</tbody>
</tgroup>
</table>
</refsect1>
<refsect1>
&return-value;
<variablelist>
<varlistentry>
<term><errorcode>EINVAL</errorcode></term>
<listitem>
<para>The &v4l2-control; <structfield>id</structfield> is
invalid or the <structfield>value</structfield> is inappropriate for
the given control (i.e. if a menu item is selected that is not supported
by the driver according to &VIDIOC-QUERYMENU;).</para>
</listitem>
</varlistentry>
<varlistentry>
<term><errorcode>ERANGE</errorcode></term>
<listitem>
<para>The &v4l2-control; <structfield>value</structfield>
is out of bounds.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><errorcode>EBUSY</errorcode></term>
<listitem>
<para>The control is temporarily not changeable, possibly
because another applications took over control of the device function
this control belongs to.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><errorcode>EACCES</errorcode></term>
<listitem>
<para>Attempt to set a read-only control or to get a
write-only control.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
</refentry>
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