Documentation/DocBook/v4l/vidioc-queryctrl.xml - pub/scm/linux/kernel/git/stable/linux-stable - 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> to

            
            <structfield>maximum</structfield>, inclusive. Note that it is possible

            
            for <constant>VIDIOC_QUERYMENU</constant> to return an &EINVAL; for some

            
            indices between <structfield>minimum</structfield> and <structfield>maximum</structfield>.

            
            In that case that particular menu item is not supported by this driver. Also note that

            
            the <structfield>minimum</structfield> value is not necessarily 0.</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 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>&ge; 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" />) + 1, 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> is

            
            invalid or <structfield>index</structfield> is out of range (less than

            
            <structfield>minimum</structfield> or greater than <structfield>maximum</structfield>)

            
            or this particular menu item is not supported by the driver.</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> to
	<structfield>maximum</structfield>, inclusive. Note that it is possible
	for <constant>VIDIOC_QUERYMENU</constant> to return an &EINVAL; for some
	indices between <structfield>minimum</structfield> and <structfield>maximum</structfield>.
	In that case that particular menu item is not supported by this driver. Also note that
	the <structfield>minimum</structfield> value is not necessarily 0.</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 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" />) + 1, 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> is
	invalid or <structfield>index</structfield> is out of range (less than
	<structfield>minimum</structfield> or greater than <structfield>maximum</structfield>)
	or this particular menu item is not supported by the driver.</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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