Documentation/DocBook/media/v4l/vidioc-g-ctrl.xml

   1 <refentry id="vidioc-g-ctrl">
   2   <refmeta>
   3     <refentrytitle>ioctl VIDIOC_G_CTRL, VIDIOC_S_CTRL</refentrytitle>
   4     &manvol;
   5   </refmeta>
   6
   7   <refnamediv>
   8     <refname>VIDIOC_G_CTRL</refname>
   9     <refname>VIDIOC_S_CTRL</refname>
  10     <refpurpose>Get or set the value of a control</refpurpose>
  11   </refnamediv>
  12
  13   <refsynopsisdiv>
  14     <funcsynopsis>
  15       <funcprototype>
  16         <funcdef>int <function>ioctl</function></funcdef>
  17         <paramdef>int <parameter>fd</parameter></paramdef>
  18         <paramdef>int <parameter>request</parameter></paramdef>
  19         <paramdef>struct v4l2_control
  20 *<parameter>argp</parameter></paramdef>
  21       </funcprototype>
  22     </funcsynopsis>
  23   </refsynopsisdiv>
  24
  25   <refsect1>
  26     <title>Arguments</title>
  27
  28     <variablelist>
  29       <varlistentry>
  30         <term><parameter>fd</parameter></term>
  31         <listitem>
  32           <para>&fd;</para>
  33         </listitem>
  34       </varlistentry>
  35       <varlistentry>
  36         <term><parameter>request</parameter></term>
  37         <listitem>
  38           <para>VIDIOC_G_CTRL, VIDIOC_S_CTRL</para>
  39         </listitem>
  40       </varlistentry>
  41       <varlistentry>
  42         <term><parameter>argp</parameter></term>
  43         <listitem>
  44           <para></para>
  45         </listitem>
  46       </varlistentry>
  47     </variablelist>
  48   </refsect1>
  49
  50   <refsect1>
  51     <title>Description</title>
  52
  53     <para>To get the current value of a control applications
  54 initialize the <structfield>id</structfield> field of a struct
  55 <structname>v4l2_control</structname> and call the
  56 <constant>VIDIOC_G_CTRL</constant> ioctl with a pointer to this
  57 structure. To change the value of a control applications initialize
  58 the <structfield>id</structfield> and <structfield>value</structfield>
  59 fields of a struct <structname>v4l2_control</structname> and call the
  60 <constant>VIDIOC_S_CTRL</constant> ioctl.</para>
  61
  62     <para>When the <structfield>id</structfield> is invalid drivers
  63 return an &EINVAL;. When the <structfield>value</structfield> is out
  64 of bounds drivers can choose to take the closest valid value or return
  65 an &ERANGE;, whatever seems more appropriate. However,
  66 <constant>VIDIOC_S_CTRL</constant> is a write-only ioctl, it does not
  67 return the actual new value. If the <structfield>value</structfield>
  68 is inappropriate for the control (e.g. if it refers to an unsupported
  69 menu index of a menu control), then &EINVAL; is returned as well.</para>
  70
  71     <para>These ioctls work only with user controls. For other
  72 control classes the &VIDIOC-G-EXT-CTRLS;, &VIDIOC-S-EXT-CTRLS; or
  73 &VIDIOC-TRY-EXT-CTRLS; must be used.</para>
  74
  75     <table pgwide="1" frame="none" id="v4l2-control">
  76       <title>struct <structname>v4l2_control</structname></title>
  77       <tgroup cols="3">
  78         &cs-str;
  79         <tbody valign="top">
  80           <row>
  81             <entry>__u32</entry>
  82             <entry><structfield>id</structfield></entry>
  83             <entry>Identifies the control, set by the
  84 application.</entry>
  85           </row>
  86           <row>
  87             <entry>__s32</entry>
  88             <entry><structfield>value</structfield></entry>
  89             <entry>New value or current value.</entry>
  90           </row>
  91         </tbody>
  92       </tgroup>
  93     </table>
  94   </refsect1>
  95
  96   <refsect1>
  97     &return-value;
  98
  99     <variablelist>
 100       <varlistentry>
 101         <term><errorcode>EINVAL</errorcode></term>
 102         <listitem>
 103           <para>The &v4l2-control; <structfield>id</structfield> is
 104 invalid or the <structfield>value</structfield> is inappropriate for
 105 the given control (i.e. if a menu item is selected that is not supported
 106 by the driver according to &VIDIOC-QUERYMENU;).</para>
 107         </listitem>
 108       </varlistentry>
 109       <varlistentry>
 110         <term><errorcode>ERANGE</errorcode></term>
 111         <listitem>
 112           <para>The &v4l2-control; <structfield>value</structfield>
 113 is out of bounds.</para>
 114         </listitem>
 115       </varlistentry>
 116       <varlistentry>
 117         <term><errorcode>EBUSY</errorcode></term>
 118         <listitem>
 119           <para>The control is temporarily not changeable, possibly
 120 because another applications took over control of the device function
 121 this control belongs to.</para>
 122         </listitem>
 123       </varlistentry>
 124       <varlistentry>
 125         <term><errorcode>EACCES</errorcode></term>
 126         <listitem>
 127           <para>Attempt to set a read-only control or to get a
 128           write-only control.</para>
 129         </listitem>
 130       </varlistentry>
 131     </variablelist>
 132   </refsect1>
 133 </refentry>