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6. vidioc-g-ctrl.xml

<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>