429 lines
16 KiB
XML
429 lines
16 KiB
XML
<refentry id="vidioc-queryctrl">
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<refmeta>
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<refentrytitle>ioctl VIDIOC_QUERYCTRL, VIDIOC_QUERYMENU</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>VIDIOC_QUERYCTRL</refname>
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<refname>VIDIOC_QUERYMENU</refname>
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<refpurpose>Enumerate controls and menu control items</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>struct v4l2_queryctrl *<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>struct v4l2_querymenu *<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Arguments</title>
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<variablelist>
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<varlistentry>
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<term><parameter>fd</parameter></term>
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<listitem>
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<para>&fd;</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>request</parameter></term>
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<listitem>
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<para>VIDIOC_QUERYCTRL, VIDIOC_QUERYMENU</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>argp</parameter></term>
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<listitem>
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<para></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Description</title>
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<para>To query the attributes of a control applications set the
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<structfield>id</structfield> field of a &v4l2-queryctrl; and call the
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<constant>VIDIOC_QUERYCTRL</constant> ioctl with a pointer to this
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structure. The driver fills the rest of the structure or returns an
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&EINVAL; when the <structfield>id</structfield> is invalid.</para>
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<para>It is possible to enumerate controls by calling
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<constant>VIDIOC_QUERYCTRL</constant> with successive
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<structfield>id</structfield> values starting from
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<constant>V4L2_CID_BASE</constant> up to and exclusive
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<constant>V4L2_CID_BASE_LASTP1</constant>. Drivers may return
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<errorcode>EINVAL</errorcode> if a control in this range is not
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supported. Further applications can enumerate private controls, which
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are not defined in this specification, by starting at
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<constant>V4L2_CID_PRIVATE_BASE</constant> and incrementing
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<structfield>id</structfield> until the driver returns
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<errorcode>EINVAL</errorcode>.</para>
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<para>In both cases, when the driver sets the
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<constant>V4L2_CTRL_FLAG_DISABLED</constant> flag in the
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<structfield>flags</structfield> field this control is permanently
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disabled and should be ignored by the application.<footnote>
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<para><constant>V4L2_CTRL_FLAG_DISABLED</constant> was
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intended for two purposes: Drivers can skip predefined controls not
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supported by the hardware (although returning EINVAL would do as
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well), or disable predefined and private controls after hardware
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detection without the trouble of reordering control arrays and indices
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(EINVAL cannot be used to skip private controls because it would
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prematurely end the enumeration).</para></footnote></para>
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<para>When the application ORs <structfield>id</structfield> with
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<constant>V4L2_CTRL_FLAG_NEXT_CTRL</constant> the driver returns the
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next supported control, or <errorcode>EINVAL</errorcode> if there is
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none. Drivers which do not support this flag yet always return
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<errorcode>EINVAL</errorcode>.</para>
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<para>Additional information is required for menu controls: the
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names of the menu items. To query them applications set the
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<structfield>id</structfield> and <structfield>index</structfield>
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fields of &v4l2-querymenu; and call the
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<constant>VIDIOC_QUERYMENU</constant> ioctl with a pointer to this
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structure. The driver fills the rest of the structure or returns an
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&EINVAL; when the <structfield>id</structfield> or
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<structfield>index</structfield> is invalid. Menu items are enumerated
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by calling <constant>VIDIOC_QUERYMENU</constant> with successive
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<structfield>index</structfield> values from &v4l2-queryctrl;
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<structfield>minimum</structfield> (0) to
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<structfield>maximum</structfield>, inclusive.</para>
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<para>See also the examples in <xref linkend="control" />.</para>
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<table pgwide="1" frame="none" id="v4l2-queryctrl">
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<title>struct <structname>v4l2_queryctrl</structname></title>
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<tgroup cols="3">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__u32</entry>
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<entry><structfield>id</structfield></entry>
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<entry>Identifies the control, set by the application. See
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<xref linkend="control-id" /> for predefined IDs. When the ID is ORed
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with V4L2_CTRL_FLAG_NEXT_CTRL the driver clears the flag and returns
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the first control with a higher ID. Drivers which do not support this
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flag yet always return an &EINVAL;.</entry>
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</row>
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<row>
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<entry>&v4l2-ctrl-type;</entry>
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<entry><structfield>type</structfield></entry>
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<entry>Type of control, see <xref
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linkend="v4l2-ctrl-type" />.</entry>
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</row>
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<row>
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<entry>__u8</entry>
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<entry><structfield>name</structfield>[32]</entry>
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<entry>Name of the control, a NUL-terminated ASCII
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string. This information is intended for the user.</entry>
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</row>
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<row>
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<entry>__s32</entry>
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<entry><structfield>minimum</structfield></entry>
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<entry>Minimum value, inclusive. This field gives a lower
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bound for <constant>V4L2_CTRL_TYPE_INTEGER</constant> controls and the
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lowest valid index (always 0) for <constant>V4L2_CTRL_TYPE_MENU</constant> controls.
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For <constant>V4L2_CTRL_TYPE_STRING</constant> controls the minimum value
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gives the minimum length of the string. This length <emphasis>does not include the terminating
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zero</emphasis>. It may not be valid for any other type of control, including
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<constant>V4L2_CTRL_TYPE_INTEGER64</constant> controls. Note that this is a
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signed value.</entry>
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</row>
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<row>
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<entry>__s32</entry>
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<entry><structfield>maximum</structfield></entry>
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<entry>Maximum value, inclusive. This field gives an upper
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bound for <constant>V4L2_CTRL_TYPE_INTEGER</constant> controls and the
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highest valid index for <constant>V4L2_CTRL_TYPE_MENU</constant>
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controls.
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For <constant>V4L2_CTRL_TYPE_STRING</constant> controls the maximum value
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gives the maximum length of the string. This length <emphasis>does not include the terminating
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zero</emphasis>. It may not be valid for any other type of control, including
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<constant>V4L2_CTRL_TYPE_INTEGER64</constant> controls. Note that this is a
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signed value.</entry>
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</row>
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<row>
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<entry>__s32</entry>
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<entry><structfield>step</structfield></entry>
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<entry><para>This field gives a step size for
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<constant>V4L2_CTRL_TYPE_INTEGER</constant> controls. For
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<constant>V4L2_CTRL_TYPE_STRING</constant> controls this field refers to
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the string length that has to be a multiple of this step size.
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It may not be valid for any other type of control, including
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<constant>V4L2_CTRL_TYPE_INTEGER64</constant>
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controls.</para><para>Generally drivers should not scale hardware
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control values. It may be necessary for example when the
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<structfield>name</structfield> or <structfield>id</structfield> imply
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a particular unit and the hardware actually accepts only multiples of
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said unit. If so, drivers must take care values are properly rounded
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when scaling, such that errors will not accumulate on repeated
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read-write cycles.</para><para>This field gives the smallest change of
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an integer control actually affecting hardware. Often the information
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is needed when the user can change controls by keyboard or GUI
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buttons, rather than a slider. When for example a hardware register
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accepts values 0-511 and the driver reports 0-65535, step should be
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128.</para><para>Note that although signed, the step value is supposed to
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be always positive.</para></entry>
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</row>
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<row>
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<entry>__s32</entry>
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<entry><structfield>default_value</structfield></entry>
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<entry>The default value of a
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<constant>V4L2_CTRL_TYPE_INTEGER</constant>,
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<constant>_BOOLEAN</constant> or <constant>_MENU</constant> control.
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Not valid for other types of controls. Drivers reset controls only
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when the driver is loaded, not later, in particular not when the
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func-open; is called.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>flags</structfield></entry>
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<entry>Control flags, see <xref
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linkend="control-flags" />.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>reserved</structfield>[2]</entry>
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<entry>Reserved for future extensions. Drivers must set
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the array to zero.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<table pgwide="1" frame="none" id="v4l2-querymenu">
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<title>struct <structname>v4l2_querymenu</structname></title>
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<tgroup cols="3">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__u32</entry>
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<entry><structfield>id</structfield></entry>
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<entry>Identifies the control, set by the application
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from the respective &v4l2-queryctrl;
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<structfield>id</structfield>.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>index</structfield></entry>
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<entry>Index of the menu item, starting at zero, set by
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the application.</entry>
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</row>
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<row>
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<entry>__u8</entry>
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<entry><structfield>name</structfield>[32]</entry>
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<entry>Name of the menu item, a NUL-terminated ASCII
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string. This information is intended for the user.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>reserved</structfield></entry>
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<entry>Reserved for future extensions. Drivers must set
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the array to zero.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<table pgwide="1" frame="none" id="v4l2-ctrl-type">
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<title>enum v4l2_ctrl_type</title>
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<tgroup cols="5" align="left">
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<colspec colwidth="30*" />
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<colspec colwidth="5*" align="center" />
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<colspec colwidth="5*" align="center" />
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<colspec colwidth="5*" align="center" />
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<colspec colwidth="55*" />
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<thead>
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<row>
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<entry>Type</entry>
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<entry><structfield>minimum</structfield></entry>
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<entry><structfield>step</structfield></entry>
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<entry><structfield>maximum</structfield></entry>
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<entry>Description</entry>
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</row>
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</thead>
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<tbody valign="top">
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<row>
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<entry><constant>V4L2_CTRL_TYPE_INTEGER</constant></entry>
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<entry>any</entry>
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<entry>any</entry>
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<entry>any</entry>
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<entry>An integer-valued control ranging from minimum to
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maximum inclusive. The step value indicates the increment between
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values which are actually different on the hardware.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CTRL_TYPE_BOOLEAN</constant></entry>
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<entry>0</entry>
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<entry>1</entry>
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<entry>1</entry>
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<entry>A boolean-valued control. Zero corresponds to
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"disabled", and one means "enabled".</entry>
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</row>
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<row>
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<entry><constant>V4L2_CTRL_TYPE_MENU</constant></entry>
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<entry>0</entry>
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<entry>1</entry>
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<entry>N-1</entry>
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<entry>The control has a menu of N choices. The names of
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the menu items can be enumerated with the
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<constant>VIDIOC_QUERYMENU</constant> ioctl.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CTRL_TYPE_BUTTON</constant></entry>
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<entry>0</entry>
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<entry>0</entry>
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<entry>0</entry>
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<entry>A control which performs an action when set.
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Drivers must ignore the value passed with
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<constant>VIDIOC_S_CTRL</constant> and return an &EINVAL; on a
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<constant>VIDIOC_G_CTRL</constant> attempt.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CTRL_TYPE_INTEGER64</constant></entry>
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<entry>n/a</entry>
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<entry>n/a</entry>
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<entry>n/a</entry>
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<entry>A 64-bit integer valued control. Minimum, maximum
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and step size cannot be queried.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CTRL_TYPE_STRING</constant></entry>
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<entry>≥ 0</entry>
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<entry>≥ 1</entry>
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<entry>≥ 0</entry>
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<entry>The minimum and maximum string lengths. The step size
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means that the string must be (minimum + N * step) characters long for
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N ≥ 0. These lengths do not include the terminating zero, so in order to
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pass a string of length 8 to &VIDIOC-S-EXT-CTRLS; you need to set the
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<structfield>size</structfield> field of &v4l2-ext-control; to 9. For &VIDIOC-G-EXT-CTRLS; you can
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set the <structfield>size</structfield> field to <structfield>maximum</structfield> + 1.
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Which character encoding is used will depend on the string control itself and
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should be part of the control documentation.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CTRL_TYPE_CTRL_CLASS</constant></entry>
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<entry>n/a</entry>
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<entry>n/a</entry>
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<entry>n/a</entry>
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<entry>This is not a control. When
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<constant>VIDIOC_QUERYCTRL</constant> is called with a control ID
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equal to a control class code (see <xref linkend="ctrl-class" />), the
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ioctl returns the name of the control class and this control type.
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Older drivers which do not support this feature return an
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&EINVAL;.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<table pgwide="1" frame="none" id="control-flags">
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<title>Control Flags</title>
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<tgroup cols="3">
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&cs-def;
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<tbody valign="top">
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<row>
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<entry><constant>V4L2_CTRL_FLAG_DISABLED</constant></entry>
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<entry>0x0001</entry>
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<entry>This control is permanently disabled and should be
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ignored by the application. Any attempt to change the control will
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result in an &EINVAL;.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CTRL_FLAG_GRABBED</constant></entry>
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<entry>0x0002</entry>
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<entry>This control is temporarily unchangeable, for
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example because another application took over control of the
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respective resource. Such controls may be displayed specially in a
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user interface. Attempts to change the control may result in an
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&EBUSY;.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CTRL_FLAG_READ_ONLY</constant></entry>
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<entry>0x0004</entry>
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<entry>This control is permanently readable only. Any
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attempt to change the control will result in an &EINVAL;.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CTRL_FLAG_UPDATE</constant></entry>
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<entry>0x0008</entry>
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<entry>A hint that changing this control may affect the
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value of other controls within the same control class. Applications
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should update their user interface accordingly.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CTRL_FLAG_INACTIVE</constant></entry>
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<entry>0x0010</entry>
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<entry>This control is not applicable to the current
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configuration and should be displayed accordingly in a user interface.
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For example the flag may be set on a MPEG audio level 2 bitrate
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control when MPEG audio encoding level 1 was selected with another
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control.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CTRL_FLAG_SLIDER</constant></entry>
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<entry>0x0020</entry>
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<entry>A hint that this control is best represented as a
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slider-like element in a user interface.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CTRL_FLAG_WRITE_ONLY</constant></entry>
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<entry>0x0040</entry>
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<entry>This control is permanently writable only. Any
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attempt to read the control will result in an &EACCES; error code. This
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flag is typically present for relative controls or action controls where
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writing a value will cause the device to carry out a given action
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(⪚ motor control) but no meaningful value can be returned.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</refsect1>
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<refsect1>
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&return-value;
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<variablelist>
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<varlistentry>
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<term><errorcode>EINVAL</errorcode></term>
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<listitem>
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<para>The &v4l2-queryctrl; <structfield>id</structfield>
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is invalid. The &v4l2-querymenu; <structfield>id</structfield> or
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<structfield>index</structfield> is invalid.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><errorcode>EACCES</errorcode></term>
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<listitem>
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<para>An attempt was made to read a write-only control.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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</refentry>
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<!--
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Local Variables:
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mode: sgml
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sgml-parent-document: "v4l2.sgml"
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indent-tabs-mode: nil
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End:
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-->
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