Documentation/DocBook/v4l/vidioc-queryctrl.xml - kernel/prism - Git at Google

 <refentry id="vidioc-queryctrl">
   <refmeta>
     <refentrytitle>ioctl VIDIOC_QUERYCTRL, VIDIOC_QUERYMENU</refentrytitle>
     &manvol;
   </refmeta>

   <refnamediv>
     <refname>VIDIOC_QUERYCTRL</refname>
     <refname>VIDIOC_QUERYMENU</refname>
     <refpurpose>Enumerate controls and menu control items</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_queryctrl *<parameter>argp</parameter></paramdef>
       </funcprototype>
     </funcsynopsis>
     <funcsynopsis>
       <funcprototype>
 	<funcdef>int <function>ioctl</function></funcdef>
 	<paramdef>int <parameter>fd</parameter></paramdef>
 	<paramdef>int <parameter>request</parameter></paramdef>
 	<paramdef>struct v4l2_querymenu *<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_QUERYCTRL, VIDIOC_QUERYMENU</para>
 	</listitem>
       </varlistentry>
       <varlistentry>
 	<term><parameter>argp</parameter></term>
 	<listitem>
 	  <para></para>
 	</listitem>
       </varlistentry>
     </variablelist>
   </refsect1>

   <refsect1>
     <title>Description</title>

     <para>To query the attributes of a control applications set the
 <structfield>id</structfield> field of a &v4l2-queryctrl; and call the
 <constant>VIDIOC_QUERYCTRL</constant> ioctl with a pointer to this
 structure. The driver fills the rest of the structure or returns an
 &EINVAL; when the <structfield>id</structfield> is invalid.</para>

     <para>It is possible to enumerate controls by calling
 <constant>VIDIOC_QUERYCTRL</constant> with successive
 <structfield>id</structfield> values starting from
 <constant>V4L2_CID_BASE</constant> up to and exclusive
 <constant>V4L2_CID_BASE_LASTP1</constant>. Drivers may return
 <errorcode>EINVAL</errorcode> if a control in this range is not
 supported. Further applications can enumerate private controls, which
 are not defined in this specification, by starting at
 <constant>V4L2_CID_PRIVATE_BASE</constant> and incrementing
 <structfield>id</structfield> until the driver returns
 <errorcode>EINVAL</errorcode>.</para>

     <para>In both cases, when the driver sets the
 <constant>V4L2_CTRL_FLAG_DISABLED</constant> flag in the
 <structfield>flags</structfield> field this control is permanently
 disabled and should be ignored by the application.<footnote>
 	<para><constant>V4L2_CTRL_FLAG_DISABLED</constant> was
 intended for two purposes: Drivers can skip predefined controls not
 supported by the hardware (although returning EINVAL would do as
 well), or disable predefined and private controls after hardware
 detection without the trouble of reordering control arrays and indices
 (EINVAL cannot be used to skip private controls because it would
 prematurely end the enumeration).</para></footnote></para>

     <para>When the application ORs <structfield>id</structfield> with
 <constant>V4L2_CTRL_FLAG_NEXT_CTRL</constant> the driver returns the
 next supported control, or <errorcode>EINVAL</errorcode> if there is
 none. Drivers which do not support this flag yet always return
 <errorcode>EINVAL</errorcode>.</para>

     <para>Additional information is required for menu controls: the
 names of the menu items. To query them applications set the
 <structfield>id</structfield> and <structfield>index</structfield>
 fields of &v4l2-querymenu; and call the
 <constant>VIDIOC_QUERYMENU</constant> ioctl with a pointer to this
 structure. The driver fills the rest of the structure or returns an
 &EINVAL; when the <structfield>id</structfield> or
 <structfield>index</structfield> is invalid. Menu items are enumerated
 by calling <constant>VIDIOC_QUERYMENU</constant> with successive
 <structfield>index</structfield> values from &v4l2-queryctrl;
 <structfield>minimum</structfield> (0) to
 <structfield>maximum</structfield>, inclusive.</para>

     <para>See also the examples in <xref linkend="control" />.</para>

     <table pgwide="1" frame="none" id="v4l2-queryctrl">
       <title>struct <structname>v4l2_queryctrl</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. See
 <xref linkend="control-id" /> for predefined IDs. When the ID is ORed
 with V4L2_CTRL_FLAG_NEXT_CTRL the driver clears the flag and returns
 the first control with a higher ID. Drivers which do not support this
 flag yet always return an &EINVAL;.</entry>
 	  </row>
 	  <row>
 	    <entry>&v4l2-ctrl-type;</entry>
 	    <entry><structfield>type</structfield></entry>
 	    <entry>Type of control, see <xref
 		linkend="v4l2-ctrl-type" />.</entry>
 	  </row>
 	  <row>
 	    <entry>__u8</entry>
 	    <entry><structfield>name</structfield>[32]</entry>
 	    <entry>Name of the control, a NUL-terminated ASCII
 string. This information is intended for the user.</entry>
 	  </row>
 	  <row>
 	    <entry>__s32</entry>
 	    <entry><structfield>minimum</structfield></entry>
 	    <entry>Minimum value, inclusive. This field gives a lower
 bound for <constant>V4L2_CTRL_TYPE_INTEGER</constant> controls and the
 lowest valid index (always 0) for <constant>V4L2_CTRL_TYPE_MENU</constant> controls.
 For <constant>V4L2_CTRL_TYPE_STRING</constant> controls the minimum value
 gives the minimum length of the string. This length <emphasis>does not include the terminating
 zero</emphasis>. It may not be valid for any other type of control, including
 <constant>V4L2_CTRL_TYPE_INTEGER64</constant> controls. Note that this is a
 signed value.</entry>
 	  </row>
 	  <row>
 	    <entry>__s32</entry>
 	    <entry><structfield>maximum</structfield></entry>
 	    <entry>Maximum value, inclusive. This field gives an upper
 bound for <constant>V4L2_CTRL_TYPE_INTEGER</constant> controls and the
 highest valid index for <constant>V4L2_CTRL_TYPE_MENU</constant>
 controls.
 For <constant>V4L2_CTRL_TYPE_STRING</constant> controls the maximum value
 gives the maximum length of the string. This length <emphasis>does not include the terminating
 zero</emphasis>. It may not be valid for any other type of control, including
 <constant>V4L2_CTRL_TYPE_INTEGER64</constant> controls. Note that this is a
 signed value.</entry>
 	  </row>
 	  <row>
 	    <entry>__s32</entry>
 	    <entry><structfield>step</structfield></entry>
 	    <entry><para>This field gives a step size for
 <constant>V4L2_CTRL_TYPE_INTEGER</constant> controls. For
 <constant>V4L2_CTRL_TYPE_STRING</constant> controls this field refers to
 the string length that has to be a multiple of this step size.
 It may not be valid for any other type of control, including
 <constant>V4L2_CTRL_TYPE_INTEGER64</constant>
 controls.</para><para>Generally drivers should not scale hardware
 control values. It may be necessary for example when the
 <structfield>name</structfield> or <structfield>id</structfield> imply
 a particular unit and the hardware actually accepts only multiples of
 said unit. If so, drivers must take care values are properly rounded
 when scaling, such that errors will not accumulate on repeated
 read-write cycles.</para><para>This field gives the smallest change of
 an integer control actually affecting hardware. Often the information
 is needed when the user can change controls by keyboard or GUI
 buttons, rather than a slider. When for example a hardware register
 accepts values 0-511 and the driver reports 0-65535, step should be
 128.</para><para>Note that although signed, the step value is supposed to
 be always positive.</para></entry>
 	  </row>
 	  <row>
 	    <entry>__s32</entry>
 	    <entry><structfield>default_value</structfield></entry>
 	    <entry>The default value of a
 <constant>V4L2_CTRL_TYPE_INTEGER</constant>,
 <constant>_BOOLEAN</constant> or <constant>_MENU</constant> control.
 Not valid for other types of controls. Drivers reset controls only
 when the driver is loaded, not later, in particular not when the
 func-open; is called.</entry>
 	  </row>
 	  <row>
 	    <entry>__u32</entry>
 	    <entry><structfield>flags</structfield></entry>
 	    <entry>Control flags, see <xref
 		linkend="control-flags" />.</entry>
 	  </row>
 	  <row>
 	    <entry>__u32</entry>
 	    <entry><structfield>reserved</structfield>[2]</entry>
 	    <entry>Reserved for future extensions. Drivers must set
 the array to zero.</entry>
 	  </row>
 	</tbody>
       </tgroup>
     </table>

     <table pgwide="1" frame="none" id="v4l2-querymenu">
       <title>struct <structname>v4l2_querymenu</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
 from the respective &v4l2-queryctrl;
 <structfield>id</structfield>.</entry>
 	  </row>
 	  <row>
 	    <entry>__u32</entry>
 	    <entry><structfield>index</structfield></entry>
 	    <entry>Index of the menu item, starting at zero, set by
 	    the application.</entry>
 	  </row>
 	  <row>
 	    <entry>__u8</entry>
 	    <entry><structfield>name</structfield>[32]</entry>
 	    <entry>Name of the menu item, a NUL-terminated ASCII
 string. This information is intended for the user.</entry>
 	  </row>
 	  <row>
 	    <entry>__u32</entry>
 	    <entry><structfield>reserved</structfield></entry>
 	    <entry>Reserved for future extensions. Drivers must set
 the array to zero.</entry>
 	  </row>
 	</tbody>
       </tgroup>
     </table>

     <table pgwide="1" frame="none" id="v4l2-ctrl-type">
       <title>enum v4l2_ctrl_type</title>
       <tgroup cols="5" align="left">
 	<colspec colwidth="30*" />
 	<colspec colwidth="5*" align="center" />
 	<colspec colwidth="5*" align="center" />
 	<colspec colwidth="5*" align="center" />
 	<colspec colwidth="55*" />
 	<thead>
 	  <row>
 	    <entry>Type</entry>
 	    <entry><structfield>minimum</structfield></entry>
 	    <entry><structfield>step</structfield></entry>
 	    <entry><structfield>maximum</structfield></entry>
 	    <entry>Description</entry>
 	  </row>
 	</thead>
 	<tbody valign="top">
 	  <row>
 	    <entry><constant>V4L2_CTRL_TYPE_INTEGER</constant></entry>
 	    <entry>any</entry>
 	    <entry>any</entry>
 	    <entry>any</entry>
 	    <entry>An integer-valued control ranging from minimum to
 maximum inclusive. The step value indicates the increment between
 values which are actually different on the hardware.</entry>
 	  </row>
 	  <row>
 	    <entry><constant>V4L2_CTRL_TYPE_BOOLEAN</constant></entry>
 	    <entry>0</entry>
 	    <entry>1</entry>
 	    <entry>1</entry>
 	    <entry>A boolean-valued control. Zero corresponds to
 "disabled", and one means "enabled".</entry>
 	  </row>
 	  <row>
 	    <entry><constant>V4L2_CTRL_TYPE_MENU</constant></entry>
 	    <entry>0</entry>
 	    <entry>1</entry>
 	    <entry>N-1</entry>
 	    <entry>The control has a menu of N choices. The names of
 the menu items can be enumerated with the
 <constant>VIDIOC_QUERYMENU</constant> ioctl.</entry>
 	  </row>
 	  <row>
 	    <entry><constant>V4L2_CTRL_TYPE_BUTTON</constant></entry>
 	    <entry>0</entry>
 	    <entry>0</entry>
 	    <entry>0</entry>
 	    <entry>A control which performs an action when set.
 Drivers must ignore the value passed with
 <constant>VIDIOC_S_CTRL</constant> and return an &EINVAL; on a
 <constant>VIDIOC_G_CTRL</constant> attempt.</entry>
 	  </row>
 	  <row>
 	    <entry><constant>V4L2_CTRL_TYPE_INTEGER64</constant></entry>
 	    <entry>n/a</entry>
 	    <entry>n/a</entry>
 	    <entry>n/a</entry>
 	    <entry>A 64-bit integer valued control. Minimum, maximum
 and step size cannot be queried.</entry>
 	  </row>
 	  <row>
 	    <entry><constant>V4L2_CTRL_TYPE_STRING</constant></entry>
 	    <entry>&ge; 0</entry>
 	    <entry>&ge; 1</entry>
 	    <entry>&ge; 0</entry>
 	    <entry>The minimum and maximum string lengths. The step size
 means that the string must be (minimum + N * step) characters long for
 N &ge; 0. These lengths do not include the terminating zero, so in order to
 pass a string of length 8 to &VIDIOC-S-EXT-CTRLS; you need to set the
 <structfield>size</structfield> field of &v4l2-ext-control; to 9. For &VIDIOC-G-EXT-CTRLS; you can
 set the <structfield>size</structfield> field to <structfield>maximum</structfield> + 1.
 Which character encoding is used will depend on the string control itself and
 should be part of the control documentation.</entry>
 	  </row>
 	  <row>
 	    <entry><constant>V4L2_CTRL_TYPE_CTRL_CLASS</constant></entry>
 	    <entry>n/a</entry>
 	    <entry>n/a</entry>
 	    <entry>n/a</entry>
 	    <entry>This is not a control. When
 <constant>VIDIOC_QUERYCTRL</constant> is called with a control ID
 equal to a control class code (see <xref linkend="ctrl-class" />), the
 ioctl returns the name of the control class and this control type.
 Older drivers which do not support this feature return an
 &EINVAL;.</entry>
 	  </row>
 	</tbody>
       </tgroup>
     </table>

     <table pgwide="1" frame="none" id="control-flags">
       <title>Control Flags</title>
       <tgroup cols="3">
 	&cs-def;
 	<tbody valign="top">
 	  <row>
 	    <entry><constant>V4L2_CTRL_FLAG_DISABLED</constant></entry>
 	    <entry>0x0001</entry>
 	    <entry>This control is permanently disabled and should be
 ignored by the application. Any attempt to change the control will
 result in an &EINVAL;.</entry>
 	  </row>
 	  <row>
 	    <entry><constant>V4L2_CTRL_FLAG_GRABBED</constant></entry>
 	    <entry>0x0002</entry>
 	    <entry>This control is temporarily unchangeable, for
 example because another application took over control of the
 respective resource. Such controls may be displayed specially in a
 user interface. Attempts to change the control may result in an
 &EBUSY;.</entry>
 	  </row>
 	  <row>
 	    <entry><constant>V4L2_CTRL_FLAG_READ_ONLY</constant></entry>
 	    <entry>0x0004</entry>
 	    <entry>This control is permanently readable only. Any
 attempt to change the control will result in an &EINVAL;.</entry>
 	  </row>
 	  <row>
 	    <entry><constant>V4L2_CTRL_FLAG_UPDATE</constant></entry>
 	    <entry>0x0008</entry>
 	    <entry>A hint that changing this control may affect the
 value of other controls within the same control class. Applications
 should update their user interface accordingly.</entry>
 	  </row>
 	  <row>
 	    <entry><constant>V4L2_CTRL_FLAG_INACTIVE</constant></entry>
 	    <entry>0x0010</entry>
 	    <entry>This control is not applicable to the current
 configuration and should be displayed accordingly in a user interface.
 For example the flag may be set on a MPEG audio level 2 bitrate
 control when MPEG audio encoding level 1 was selected with another
 control.</entry>
 	  </row>
 	  <row>
 	    <entry><constant>V4L2_CTRL_FLAG_SLIDER</constant></entry>
 	    <entry>0x0020</entry>
 	    <entry>A hint that this control is best represented as a
 slider-like element in a user interface.</entry>
 	  </row>
 	  <row>
 	    <entry><constant>V4L2_CTRL_FLAG_WRITE_ONLY</constant></entry>
 	    <entry>0x0040</entry>
 	    <entry>This control is permanently writable only. Any
 attempt to read the control will result in an &EACCES; error code. This
 flag is typically present for relative controls or action controls where
 writing a value will cause the device to carry out a given action
 (&eg; motor control) but no meaningful value can be returned.</entry>
 	  </row>
 	</tbody>
       </tgroup>
     </table>
   </refsect1>

   <refsect1>
     &return-value;

     <variablelist>
       <varlistentry>
 	<term><errorcode>EINVAL</errorcode></term>
 	<listitem>
 	  <para>The &v4l2-queryctrl; <structfield>id</structfield>
 is invalid. The &v4l2-querymenu; <structfield>id</structfield> or
 <structfield>index</structfield> is invalid.</para>
 	</listitem>
       </varlistentry>
       <varlistentry>
 	<term><errorcode>EACCES</errorcode></term>
 	<listitem>
 	  <para>An attempt was made to read a write-only control.</para>
 	</listitem>
       </varlistentry>
     </variablelist>
   </refsect1>
 </refentry>

 <!--
 Local Variables:
 mode: sgml
 sgml-parent-document: "v4l2.sgml"
 indent-tabs-mode: nil
 End:
 -->
	<refentry id="vidioc-queryctrl">
	<refmeta>
	<refentrytitle>ioctl VIDIOC_QUERYCTRL, VIDIOC_QUERYMENU</refentrytitle>
	&manvol;
	</refmeta>

	<refnamediv>
	<refname>VIDIOC_QUERYCTRL</refname>
	<refname>VIDIOC_QUERYMENU</refname>
	<refpurpose>Enumerate controls and menu control items</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_queryctrl *<parameter>argp</parameter></paramdef>
	</funcprototype>
	</funcsynopsis>
	<funcsynopsis>
	<funcprototype>
	<funcdef>int <function>ioctl</function></funcdef>
	<paramdef>int <parameter>fd</parameter></paramdef>
	<paramdef>int <parameter>request</parameter></paramdef>
	<paramdef>struct v4l2_querymenu *<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_QUERYCTRL, VIDIOC_QUERYMENU</para>
	</listitem>
	</varlistentry>
	<varlistentry>
	<term><parameter>argp</parameter></term>
	<listitem>
	<para></para>
	</listitem>
	</varlistentry>
	</variablelist>
	</refsect1>

	<refsect1>
	<title>Description</title>

	<para>To query the attributes of a control applications set the
	<structfield>id</structfield> field of a &v4l2-queryctrl; and call the
	<constant>VIDIOC_QUERYCTRL</constant> ioctl with a pointer to this
	structure. The driver fills the rest of the structure or returns an
	&EINVAL; when the <structfield>id</structfield> is invalid.</para>

	<para>It is possible to enumerate controls by calling
	<constant>VIDIOC_QUERYCTRL</constant> with successive
	<structfield>id</structfield> values starting from
	<constant>V4L2_CID_BASE</constant> up to and exclusive
	<constant>V4L2_CID_BASE_LASTP1</constant>. Drivers may return
	<errorcode>EINVAL</errorcode> if a control in this range is not
	supported. Further applications can enumerate private controls, which
	are not defined in this specification, by starting at
	<constant>V4L2_CID_PRIVATE_BASE</constant> and incrementing
	<structfield>id</structfield> until the driver returns
	<errorcode>EINVAL</errorcode>.</para>

	<para>In both cases, when the driver sets the
	<constant>V4L2_CTRL_FLAG_DISABLED</constant> flag in the
	<structfield>flags</structfield> field this control is permanently
	disabled and should be ignored by the application.<footnote>
	<para><constant>V4L2_CTRL_FLAG_DISABLED</constant> was
	intended for two purposes: Drivers can skip predefined controls not
	supported by the hardware (although returning EINVAL would do as
	well), or disable predefined and private controls after hardware
	detection without the trouble of reordering control arrays and indices
	(EINVAL cannot be used to skip private controls because it would
	prematurely end the enumeration).</para></footnote></para>

	<para>When the application ORs <structfield>id</structfield> with
	<constant>V4L2_CTRL_FLAG_NEXT_CTRL</constant> the driver returns the
	next supported control, or <errorcode>EINVAL</errorcode> if there is
	none. Drivers which do not support this flag yet always return
	<errorcode>EINVAL</errorcode>.</para>

	<para>Additional information is required for menu controls: the
	names of the menu items. To query them applications set the
	<structfield>id</structfield> and <structfield>index</structfield>
	fields of &v4l2-querymenu; and call the
	<constant>VIDIOC_QUERYMENU</constant> ioctl with a pointer to this
	structure. The driver fills the rest of the structure or returns an
	&EINVAL; when the <structfield>id</structfield> or
	<structfield>index</structfield> is invalid. Menu items are enumerated
	by calling <constant>VIDIOC_QUERYMENU</constant> with successive
	<structfield>index</structfield> values from &v4l2-queryctrl;
	<structfield>minimum</structfield> (0) to
	<structfield>maximum</structfield>, inclusive.</para>

	<para>See also the examples in <xref linkend="control" />.</para>

	<table pgwide="1" frame="none" id="v4l2-queryctrl">
	<title>struct <structname>v4l2_queryctrl</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. See
	<xref linkend="control-id" /> for predefined IDs. When the ID is ORed
	with V4L2_CTRL_FLAG_NEXT_CTRL the driver clears the flag and returns
	the first control with a higher ID. Drivers which do not support this
	flag yet always return an &EINVAL;.</entry>
	</row>
	<row>
	<entry>&v4l2-ctrl-type;</entry>
	<entry><structfield>type</structfield></entry>
	<entry>Type of control, see <xref
	linkend="v4l2-ctrl-type" />.</entry>
	</row>
	<row>
	<entry>__u8</entry>
	<entry><structfield>name</structfield>[32]</entry>
	<entry>Name of the control, a NUL-terminated ASCII
	string. This information is intended for the user.</entry>
	</row>
	<row>
	<entry>__s32</entry>
	<entry><structfield>minimum</structfield></entry>
	<entry>Minimum value, inclusive. This field gives a lower
	bound for <constant>V4L2_CTRL_TYPE_INTEGER</constant> controls and the
	lowest valid index (always 0) for <constant>V4L2_CTRL_TYPE_MENU</constant> controls.
	For <constant>V4L2_CTRL_TYPE_STRING</constant> controls the minimum value
	gives the minimum length of the string. This length <emphasis>does not include the terminating
	zero</emphasis>. It may not be valid for any other type of control, including
	<constant>V4L2_CTRL_TYPE_INTEGER64</constant> controls. Note that this is a
	signed value.</entry>
	</row>
	<row>
	<entry>__s32</entry>
	<entry><structfield>maximum</structfield></entry>
	<entry>Maximum value, inclusive. This field gives an upper
	bound for <constant>V4L2_CTRL_TYPE_INTEGER</constant> controls and the
	highest valid index for <constant>V4L2_CTRL_TYPE_MENU</constant>
	controls.
	For <constant>V4L2_CTRL_TYPE_STRING</constant> controls the maximum value
	gives the maximum length of the string. This length <emphasis>does not include the terminating
	zero</emphasis>. It may not be valid for any other type of control, including
	<constant>V4L2_CTRL_TYPE_INTEGER64</constant> controls. Note that this is a
	signed value.</entry>
	</row>
	<row>
	<entry>__s32</entry>
	<entry><structfield>step</structfield></entry>
	<entry><para>This field gives a step size for
	<constant>V4L2_CTRL_TYPE_INTEGER</constant> controls. For
	<constant>V4L2_CTRL_TYPE_STRING</constant> controls this field refers to
	the string length that has to be a multiple of this step size.
	It may not be valid for any other type of control, including
	<constant>V4L2_CTRL_TYPE_INTEGER64</constant>
	controls.</para><para>Generally drivers should not scale hardware
	control values. It may be necessary for example when the
	<structfield>name</structfield> or <structfield>id</structfield> imply
	a particular unit and the hardware actually accepts only multiples of
	said unit. If so, drivers must take care values are properly rounded
	when scaling, such that errors will not accumulate on repeated
	read-write cycles.</para><para>This field gives the smallest change of
	an integer control actually affecting hardware. Often the information
	is needed when the user can change controls by keyboard or GUI
	buttons, rather than a slider. When for example a hardware register
	accepts values 0-511 and the driver reports 0-65535, step should be
	128.</para><para>Note that although signed, the step value is supposed to
	be always positive.</para></entry>
	</row>
	<row>
	<entry>__s32</entry>
	<entry><structfield>default_value</structfield></entry>
	<entry>The default value of a
	<constant>V4L2_CTRL_TYPE_INTEGER</constant>,
	<constant>_BOOLEAN</constant> or <constant>_MENU</constant> control.
	Not valid for other types of controls. Drivers reset controls only
	when the driver is loaded, not later, in particular not when the
	func-open; is called.</entry>
	</row>
	<row>
	<entry>__u32</entry>
	<entry><structfield>flags</structfield></entry>
	<entry>Control flags, see <xref
	linkend="control-flags" />.</entry>
	</row>
	<row>
	<entry>__u32</entry>
	<entry><structfield>reserved</structfield>[2]</entry>
	<entry>Reserved for future extensions. Drivers must set
	the array to zero.</entry>
	</row>
	</tbody>
	</tgroup>
	</table>

	<table pgwide="1" frame="none" id="v4l2-querymenu">
	<title>struct <structname>v4l2_querymenu</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
	from the respective &v4l2-queryctrl;
	<structfield>id</structfield>.</entry>
	</row>
	<row>
	<entry>__u32</entry>
	<entry><structfield>index</structfield></entry>
	<entry>Index of the menu item, starting at zero, set by
	the application.</entry>
	</row>
	<row>
	<entry>__u8</entry>
	<entry><structfield>name</structfield>[32]</entry>
	<entry>Name of the menu item, a NUL-terminated ASCII
	string. This information is intended for the user.</entry>
	</row>
	<row>
	<entry>__u32</entry>
	<entry><structfield>reserved</structfield></entry>
	<entry>Reserved for future extensions. Drivers must set
	the array to zero.</entry>
	</row>
	</tbody>
	</tgroup>
	</table>

	<table pgwide="1" frame="none" id="v4l2-ctrl-type">
	<title>enum v4l2_ctrl_type</title>
	<tgroup cols="5" align="left">
	<colspec colwidth="30*" />
	<colspec colwidth="5*" align="center" />
	<colspec colwidth="5*" align="center" />
	<colspec colwidth="5*" align="center" />
	<colspec colwidth="55*" />
	<thead>
	<row>
	<entry>Type</entry>
	<entry><structfield>minimum</structfield></entry>
	<entry><structfield>step</structfield></entry>
	<entry><structfield>maximum</structfield></entry>
	<entry>Description</entry>
	</row>
	</thead>
	<tbody valign="top">
	<row>
	<entry><constant>V4L2_CTRL_TYPE_INTEGER</constant></entry>
	<entry>any</entry>
	<entry>any</entry>
	<entry>any</entry>
	<entry>An integer-valued control ranging from minimum to
	maximum inclusive. The step value indicates the increment between
	values which are actually different on the hardware.</entry>
	</row>
	<row>
	<entry><constant>V4L2_CTRL_TYPE_BOOLEAN</constant></entry>
	<entry>0</entry>
	<entry>1</entry>
	<entry>1</entry>
	<entry>A boolean-valued control. Zero corresponds to
	"disabled", and one means "enabled".</entry>
	</row>
	<row>
	<entry><constant>V4L2_CTRL_TYPE_MENU</constant></entry>
	<entry>0</entry>
	<entry>1</entry>
	<entry>N-1</entry>
	<entry>The control has a menu of N choices. The names of
	the menu items can be enumerated with the
	<constant>VIDIOC_QUERYMENU</constant> ioctl.</entry>
	</row>
	<row>
	<entry><constant>V4L2_CTRL_TYPE_BUTTON</constant></entry>
	<entry>0</entry>
	<entry>0</entry>
	<entry>0</entry>
	<entry>A control which performs an action when set.
	Drivers must ignore the value passed with
	<constant>VIDIOC_S_CTRL</constant> and return an &EINVAL; on a
	<constant>VIDIOC_G_CTRL</constant> attempt.</entry>
	</row>
	<row>
	<entry><constant>V4L2_CTRL_TYPE_INTEGER64</constant></entry>
	<entry>n/a</entry>
	<entry>n/a</entry>
	<entry>n/a</entry>
	<entry>A 64-bit integer valued control. Minimum, maximum
	and step size cannot be queried.</entry>
	</row>
	<row>
	<entry><constant>V4L2_CTRL_TYPE_STRING</constant></entry>
	<entry>≥ 0</entry>
	<entry>≥ 1</entry>
	<entry>≥ 0</entry>
	<entry>The minimum and maximum string lengths. The step size
	means that the string must be (minimum + N * step) characters long for
	N ≥ 0. These lengths do not include the terminating zero, so in order to
	pass a string of length 8 to &VIDIOC-S-EXT-CTRLS; you need to set the
	<structfield>size</structfield> field of &v4l2-ext-control; to 9. For &VIDIOC-G-EXT-CTRLS; you can
	set the <structfield>size</structfield> field to <structfield>maximum</structfield> + 1.
	Which character encoding is used will depend on the string control itself and
	should be part of the control documentation.</entry>
	</row>
	<row>
	<entry><constant>V4L2_CTRL_TYPE_CTRL_CLASS</constant></entry>
	<entry>n/a</entry>
	<entry>n/a</entry>
	<entry>n/a</entry>
	<entry>This is not a control. When
	<constant>VIDIOC_QUERYCTRL</constant> is called with a control ID
	equal to a control class code (see <xref linkend="ctrl-class" />), the
	ioctl returns the name of the control class and this control type.
	Older drivers which do not support this feature return an
	&EINVAL;.</entry>
	</row>
	</tbody>
	</tgroup>
	</table>

	<table pgwide="1" frame="none" id="control-flags">
	<title>Control Flags</title>
	<tgroup cols="3">
	&cs-def;
	<tbody valign="top">
	<row>
	<entry><constant>V4L2_CTRL_FLAG_DISABLED</constant></entry>
	<entry>0x0001</entry>
	<entry>This control is permanently disabled and should be
	ignored by the application. Any attempt to change the control will
	result in an &EINVAL;.</entry>
	</row>
	<row>
	<entry><constant>V4L2_CTRL_FLAG_GRABBED</constant></entry>
	<entry>0x0002</entry>
	<entry>This control is temporarily unchangeable, for
	example because another application took over control of the
	respective resource. Such controls may be displayed specially in a
	user interface. Attempts to change the control may result in an
	&EBUSY;.</entry>
	</row>
	<row>
	<entry><constant>V4L2_CTRL_FLAG_READ_ONLY</constant></entry>
	<entry>0x0004</entry>
	<entry>This control is permanently readable only. Any
	attempt to change the control will result in an &EINVAL;.</entry>
	</row>
	<row>
	<entry><constant>V4L2_CTRL_FLAG_UPDATE</constant></entry>
	<entry>0x0008</entry>
	<entry>A hint that changing this control may affect the
	value of other controls within the same control class. Applications
	should update their user interface accordingly.</entry>
	</row>
	<row>
	<entry><constant>V4L2_CTRL_FLAG_INACTIVE</constant></entry>
	<entry>0x0010</entry>
	<entry>This control is not applicable to the current
	configuration and should be displayed accordingly in a user interface.
	For example the flag may be set on a MPEG audio level 2 bitrate
	control when MPEG audio encoding level 1 was selected with another
	control.</entry>
	</row>
	<row>
	<entry><constant>V4L2_CTRL_FLAG_SLIDER</constant></entry>
	<entry>0x0020</entry>
	<entry>A hint that this control is best represented as a
	slider-like element in a user interface.</entry>
	</row>
	<row>
	<entry><constant>V4L2_CTRL_FLAG_WRITE_ONLY</constant></entry>
	<entry>0x0040</entry>
	<entry>This control is permanently writable only. Any
	attempt to read the control will result in an &EACCES; error code. This
	flag is typically present for relative controls or action controls where
	writing a value will cause the device to carry out a given action
	(&eg; motor control) but no meaningful value can be returned.</entry>
	</row>
	</tbody>
	</tgroup>
	</table>
	</refsect1>

	<refsect1>
	&return-value;

	<variablelist>
	<varlistentry>
	<term><errorcode>EINVAL</errorcode></term>
	<listitem>
	<para>The &v4l2-queryctrl; <structfield>id</structfield>
	is invalid. The &v4l2-querymenu; <structfield>id</structfield> or
	<structfield>index</structfield> is invalid.</para>
	</listitem>
	</varlistentry>
	<varlistentry>
	<term><errorcode>EACCES</errorcode></term>
	<listitem>
	<para>An attempt was made to read a write-only control.</para>
	</listitem>
	</varlistentry>
	</variablelist>
	</refsect1>
	</refentry>

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