path: root/Documentation/DocBook/v4l/vidioc-g-ext-ctrls.xml

<refentry id="vidioc-g-ext-ctrls">
  <refmeta>
    <refentrytitle>ioctl VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS,
VIDIOC_TRY_EXT_CTRLS</refentrytitle>
    &manvol;
  </refmeta>

  <refnamediv>
    <refname>VIDIOC_G_EXT_CTRLS</refname>
    <refname>VIDIOC_S_EXT_CTRLS</refname>
    <refname>VIDIOC_TRY_EXT_CTRLS</refname>
    <refpurpose>Get or set the value of several controls, try control
values</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_ext_controls
*<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_EXT_CTRLS, VIDIOC_S_EXT_CTRLS,
VIDIOC_TRY_EXT_CTRLS</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>argp</parameter></term>
	<listitem>
	  <para></para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Description</title>

    <para>These ioctls allow the caller to get or set multiple
controls atomically. Control IDs are grouped into control classes (see
<xref linkend="ctrl-class" />) and all controls in the control array
must belong to the same control class.</para>

    <para>Applications must always fill in the
<structfield>count</structfield>,
<structfield>ctrl_class</structfield>,
<structfield>controls</structfield> and
<structfield>reserved</structfield> fields of &v4l2-ext-controls;, and
initialize the &v4l2-ext-control; array pointed to by the
<structfield>controls</structfield> fields.</para>

    <para>To get the current value of a set of controls applications
initialize the <structfield>id</structfield>,
<structfield>size</structfield> and <structfield>reserved2</structfield> fields
of each &v4l2-ext-control; and call the
<constant>VIDIOC_G_EXT_CTRLS</constant> ioctl. String controls controls
must also set the <structfield>string</structfield> field.</para>

    <para>If the <structfield>size</structfield> is too small to
receive the control result (only relevant for pointer-type controls
like strings), then the driver will set <structfield>size</structfield>
to a valid value and return an &ENOSPC;. You should re-allocate the
string memory to this new size and try again. It is possible that the
same issue occurs again if the string has grown in the meantime. It is
recommended to call &VIDIOC-QUERYCTRL; first and use
<structfield>maximum</structfield>+1 as the new <structfield>size</structfield>
value. It is guaranteed that that is sufficient memory.
</para>

    <para>To change the value of a set of controls applications
initialize the <structfield>id</structfield>, <structfield>size</structfield>,
<structfield>reserved2</structfield> and
<structfield>value/string</structfield> fields of each &v4l2-ext-control; and
call the <constant>VIDIOC_S_EXT_CTRLS</constant> ioctl. The controls
will only be set if <emphasis>all</emphasis> control values are
valid.</para>

    <para>To check if a set of controls have correct values applications
initialize the <structfield>id</structfield>, <structfield>size</structfield>,
<structfield>reserved2</structfield> and
<structfield>value/string</structfield> fields of each &v4l2-ext-control; and
call the <constant>VIDIOC_TRY_EXT_CTRLS</constant> ioctl. It is up to
the driver whether wrong values are automatically adjusted to a valid
value or if an error is returned.</para>

    <para>When the <structfield>id</structfield> or
<structfield>ctrl_class</structfield> is invalid drivers return an
&EINVAL;. When the value is out of bounds drivers can choose to take
the closest valid value or return an &ERANGE;, whatever seems more
appropriate. In the first case the new value is set in
&v4l2-ext-control;.</para>

    <para>The driver will only set/get these controls if all control
values are correct. This prevents the situation where only some of the
controls were set/get. Only low-level errors (&eg; a failed i2c
command) can still cause this situation.</para>

    <table pgwide="1" frame="none" id="v4l2-ext-control">
      <title>struct <structname>v4l2_ext_control</structname></title>
      <tgroup cols="4">
	&cs-ustr;
	<tbody valign="top">
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>id</structfield></entry>
	    <entry></entry>
	    <entry>Identifies the control, set by the
application.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>size</structfield></entry>
	    <entry></entry>
	    <entry>The total size in bytes of the payload of this
control. This is normally 0, but for pointer controls this should be
set to the size of the memory containing the payload, or that will
receive the payload. If <constant>VIDIOC_G_EXT_CTRLS</constant> finds
that this value is less than is required to store
the payload result, then it is set to a value large enough to store the
payload result and ENOSPC is returned. Note that for string controls
this <structfield>size</structfield> field should not be confused with the length of the string.
This field refers to the size of the memory that contains the string.
The actual <emphasis>length</emphasis> of the string may well be much smaller.
</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>reserved2</structfield>[1]</entry>
	    <entry></entry>
	    <entry>Reserved for future extensions. Drivers and
applications must set the array to zero.</entry>
	  </row>
	  <row>
	    <entry>union</entry>
	    <entry>(anonymous)</entry>
	  </row>
	  <row>
	    <entry></entry>
	    <entry>__s32</entry>
	    <entry><structfield>value</structfield></entry>
	    <entry>New value or current value.</entry>
	  </row>
	  <row>
	    <entry></entry>
	    <entry>__s64</entry>
	    <entry><structfield>value64</structfield></entry>
	    <entry>New value or current value.</entry>
	  </row>
	  <row>
	    <entry></entry>
	    <entry>char *</entry>
	    <entry><structfield>string</structfield></entry>
	    <entry>A pointer to a string.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table pgwide="1" frame="none" id="v4l2-ext-controls">
      <title>struct <structname>v4l2_ext_controls</structname></title>
      <tgroup cols="3">
	&cs-str;
	<tbody valign="top">
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>ctrl_class</structfield></entry>
	    <entry>The control class to which all controls belong, see
<xref linkend="ctrl-class" />.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>count</structfield></entry>
	    <entry>The number of controls in the controls array. May
also be zero.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>error_idx</structfield></entry>
	    <entry>Set by the driver in case of an error. It is the
index of the control causing the error or equal to 'count' when the
error is not associated with a particular control. Undefined when the
ioctl returns 0 (success).</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>reserved</structfield>[2]</entry>
	    <entry>Reserved for future extensions. Drivers and
applications must set the array to zero.</entry>
	  </row>
	  <row>
	    <entry>&v4l2-ext-control; *</entry>
	    <entry><structfield>controls</structfield></entry>
	    <entry>Pointer to an array of
<structfield>count</structfield> v4l2_ext_control structures. Ignored
if <structfield>count</structfield> equals zero.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table pgwide="1" frame="none" id="ctrl-class">
      <title>Control classes</title>
      <tgroup cols="3">
	&cs-def;
	<tbody valign="top">
	  <row>
	    <entry><constant>V4L2_CTRL_CLASS_USER</constant></entry>
	    <entry>0x980000</entry>
	    <entry>The class containing user controls. These controls
are described in <xref linkend="control" />. All controls that can be set
using the &VIDIOC-S-CTRL; and &VIDIOC-G-CTRL; ioctl belong to this
class.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CTRL_CLASS_MPEG</constant></entry>
	    <entry>0x990000</entry>
	    <entry>The class containing MPEG compression controls.
These controls are described in <xref
		linkend="mpeg-controls" />.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CTRL_CLASS_CAMERA</constant></entry>
	    <entry>0x9a0000</entry>
	    <entry>The class containing camera controls.
These controls are described in <xref
		linkend="camera-controls" />.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CTRL_CLASS_FM_TX</constant></entry>
	    <entry>0x9b0000</entry>
	    <entry>The class containing FM Transmitter (FM TX) controls.
These controls are described in <xref
		linkend="fm-tx-controls" />.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

  </refsect1>

  <refsect1>
    &return-value;

    <variablelist>
      <varlistentry>
	<term><errorcode>EINVAL</errorcode></term>
	<listitem>
	  <para>The &v4l2-ext-control; <structfield>id</structfield>
is invalid or the &v4l2-ext-controls;
<structfield>ctrl_class</structfield> is invalid. This error code is
also returned by the <constant>VIDIOC_S_EXT_CTRLS</constant> and
<constant>VIDIOC_TRY_EXT_CTRLS</constant> ioctls if two or more
control values are in conflict.</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><errorcode>ERANGE</errorcode></term>
	<listitem>
	  <para>The &v4l2-ext-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>ENOSPC</errorcode></term>
	<listitem>
	  <para>The space reserved for the control's payload is insufficient.
The field <structfield>size</structfield> is set to a value that is enough
to store the payload and this error code is returned.</para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>
</refentry>

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