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-<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>__u32</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_BITMASK</constant> controls it is the
-set of usable bits.
-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="4">
- &cs-str;
- <tbody valign="top">
- <row>
- <entry>__u32</entry>
- <entry></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></entry>
- <entry><structfield>index</structfield></entry>
- <entry>Index of the menu item, starting at zero, set by
- the application.</entry>
- </row>
- <row>
- <entry>union</entry>
- <entry></entry>
- <entry></entry>
- <entry></entry>
- </row>
- <row>
- <entry></entry>
- <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. This field is valid
-for <constant>V4L2_CTRL_FLAG_MENU</constant> type controls.</entry>
- </row>
- <row>
- <entry></entry>
- <entry>__s64</entry>
- <entry><structfield>value</structfield></entry>
- <entry>
- Value of the integer menu item. This field is valid for
- <constant>V4L2_CTRL_FLAG_INTEGER_MENU</constant> type
- controls.
- </entry>
- </row>
- <row>
- <entry>__u32</entry>
- <entry></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_INTEGER_MENU</constant></entry>
- <entry>&ge; 0</entry>
- <entry>1</entry>
- <entry>N-1</entry>
- <entry>
- The control has a menu of N choices. The values of the
- menu items can be enumerated with the
- <constant>VIDIOC_QUERYMENU</constant> ioctl. This is
- similar to <constant>V4L2_CTRL_TYPE_MENU</constant>
- except that instead of strings, the menu items are
- signed 64-bit integers.
- </entry>
- </row>
- <row>
- <entry><constant>V4L2_CTRL_TYPE_BITMASK</constant></entry>
- <entry>0</entry>
- <entry>n/a</entry>
- <entry>any</entry>
- <entry>A bitmask field. The maximum value is the set of bits that can
-be used, all other bits are to be 0. The maximum value is interpreted as a __u32,
-allowing the use of bit 31 in the bitmask.</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>
- <row>
- <entry><constant>V4L2_CTRL_FLAG_VOLATILE</constant></entry>
- <entry>0x0080</entry>
- <entry>This control is volatile, which means that the value of the control
-changes continuously. A typical example would be the current gain value if the device
-is in auto-gain mode. In such a case the hardware calculates the gain value based on
-the lighting conditions which can change over time. Note that setting a new value for
-a volatile control will have no effect. The new value will just be ignored.</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>