1 <refentry id=
"vidioc-g-ctrl">
3 <refentrytitle>ioctl VIDIOC_G_CTRL, VIDIOC_S_CTRL
</refentrytitle>
8 <refname>VIDIOC_G_CTRL
</refname>
9 <refname>VIDIOC_S_CTRL
</refname>
10 <refpurpose>Get or set the value of a control
</refpurpose>
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>
26 <title>Arguments
</title>
30 <term><parameter>fd
</parameter></term>
36 <term><parameter>request
</parameter></term>
38 <para>VIDIOC_G_CTRL, VIDIOC_S_CTRL
</para>
42 <term><parameter>argp
</parameter></term>
51 <title>Description
</title>
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>
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.
</para>
69 <para>These ioctls work only with user controls. For other
70 control classes the &VIDIOC-G-EXT-CTRLS;, &VIDIOC-S-EXT-CTRLS; or
71 &VIDIOC-TRY-EXT-CTRLS; must be used.
</para>
73 <table pgwide=
"1" frame=
"none" id=
"v4l2-control">
74 <title>struct
<structname>v4l2_control
</structname></title>
80 <entry><structfield>id
</structfield></entry>
81 <entry>Identifies the control, set by the
86 <entry><structfield>value
</structfield></entry>
87 <entry>New value or current value.
</entry>
99 <term><errorcode>EINVAL
</errorcode></term>
101 <para>The &v4l2-control;
<structfield>id
</structfield> is
106 <term><errorcode>ERANGE
</errorcode></term>
108 <para>The &v4l2-control;
<structfield>value
</structfield>
109 is out of bounds.
</para>
113 <term><errorcode>EBUSY
</errorcode></term>
115 <para>The control is temporarily not changeable, possibly
116 because another applications took over control of the device function
117 this control belongs to.
</para>
121 <term><errorcode>EACCES
</errorcode></term>
123 <para>Attempt to set a read-only control or to get a
124 write-only control.
</para>
134 sgml-parent-document: "v4l2.sgml"
135 indent-tabs-mode: nil