1<html><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968"><title>ioctl VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL, VIDIOC_QUERYMENU</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="index.html" title="LINUX MEDIA INFRASTRUCTURE API"><link rel="up" href="user-func.html" title="Appendix A. Function Reference"><link rel="prev" href="vidioc-querycap.html" title="ioctl VIDIOC_QUERYCAP"><link rel="next" href="vidioc-query-dv-timings.html" title="ioctl VIDIOC_QUERY_DV_TIMINGS"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">ioctl VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL, VIDIOC_QUERYMENU</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="vidioc-querycap.html">Prev</a> </td><th width="60%" align="center">Appendix A. Function Reference</th><td width="20%" align="right"> <a accesskey="n" href="vidioc-query-dv-timings.html">Next</a></td></tr></table><hr></div><div class="refentry"><a name="vidioc-queryctrl"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL, VIDIOC_QUERYMENU — Enumerate controls and menu control items</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><div class="funcsynopsis"><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">ioctl</b>(</code></td><td>int <var class="pdparam">fd</var>, </td></tr><tr><td> </td><td>int <var class="pdparam">request</var>, </td></tr><tr><td> </td><td>struct v4l2_queryctrl *<var class="pdparam">argp</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div><div class="funcsynopsis"><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">ioctl</b>(</code></td><td>int <var class="pdparam">fd</var>, </td></tr><tr><td> </td><td>int <var class="pdparam">request</var>, </td></tr><tr><td> </td><td>struct v4l2_query_ext_ctrl *<var class="pdparam">argp</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div><div class="funcsynopsis"><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">ioctl</b>(</code></td><td>int <var class="pdparam">fd</var>, </td></tr><tr><td> </td><td>int <var class="pdparam">request</var>, </td></tr><tr><td> </td><td>struct v4l2_querymenu *<var class="pdparam">argp</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1"><a name="idp1115925156"></a><h2>Arguments</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="parameter"><code>fd</code></em></span></dt><dd><p>File descriptor returned by <a class="link" href="func-open.html" title="V4L2 open()"><code class="function">open()</code></a>.</p></dd><dt><span class="term"><em class="parameter"><code>request</code></em></span></dt><dd><p>VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL, VIDIOC_QUERYMENU</p></dd><dt><span class="term"><em class="parameter"><code>argp</code></em></span></dt><dd><p></p></dd></dl></div></div><div class="refsect1"><a name="idp1115929284"></a><h2>Description</h2><p>To query the attributes of a control applications set the 2<em class="structfield"><code>id</code></em> field of a struct <a class="link" href="vidioc-queryctrl.html#v4l2-queryctrl" title="Table A.95. struct v4l2_queryctrl">v4l2_queryctrl</a> and call the 3<code class="constant">VIDIOC_QUERYCTRL</code> ioctl with a pointer to this 4structure. The driver fills the rest of the structure or returns an 5<span class="errorcode">EINVAL</span> error code when the <em class="structfield"><code>id</code></em> is invalid.</p><p>It is possible to enumerate controls by calling 6<code class="constant">VIDIOC_QUERYCTRL</code> with successive 7<em class="structfield"><code>id</code></em> values starting from 8<code class="constant">V4L2_CID_BASE</code> up to and exclusive 9<code class="constant">V4L2_CID_LASTP1</code>. Drivers may return 10<span class="errorcode">EINVAL</span> if a control in this range is not 11supported. Further applications can enumerate private controls, which 12are not defined in this specification, by starting at 13<code class="constant">V4L2_CID_PRIVATE_BASE</code> and incrementing 14<em class="structfield"><code>id</code></em> until the driver returns 15<span class="errorcode">EINVAL</span>.</p><p>In both cases, when the driver sets the 16<code class="constant">V4L2_CTRL_FLAG_DISABLED</code> flag in the 17<em class="structfield"><code>flags</code></em> field this control is permanently 18disabled and should be ignored by the application.<a href="#ftn.idp1115934660" class="footnote" name="idp1115934660"><sup class="footnote">[19]</sup></a></p><p>When the application ORs <em class="structfield"><code>id</code></em> with 19<code class="constant">V4L2_CTRL_FLAG_NEXT_CTRL</code> the driver returns the 20next supported non-compound control, or <span class="errorcode">EINVAL</span> 21if there is none. In addition, the <code class="constant">V4L2_CTRL_FLAG_NEXT_COMPOUND</code> 22flag can be specified to enumerate all compound controls (i.e. controls 23with type ≥ <code class="constant">V4L2_CTRL_COMPOUND_TYPES</code>). Specify both 24<code class="constant">V4L2_CTRL_FLAG_NEXT_CTRL</code> and 25<code class="constant">V4L2_CTRL_FLAG_NEXT_COMPOUND</code> in order to enumerate 26all controls, compound or not. Drivers which do not support these flags yet 27always return <span class="errorcode">EINVAL</span>.</p><p>The <code class="constant">VIDIOC_QUERY_EXT_CTRL</code> ioctl was 28introduced in order to better support controls that can use compound 29types, and to expose additional control information that cannot be 30returned in struct <a class="link" href="vidioc-queryctrl.html#v4l2-queryctrl" title="Table A.95. struct v4l2_queryctrl">v4l2_queryctrl</a> since that structure is full.</p><p><code class="constant">VIDIOC_QUERY_EXT_CTRL</code> is used in the 31same way as <code class="constant">VIDIOC_QUERYCTRL</code>, except that the 32<em class="structfield"><code>reserved</code></em> array must be zeroed as well.</p><p>Additional information is required for menu controls: the 33names of the menu items. To query them applications set the 34<em class="structfield"><code>id</code></em> and <em class="structfield"><code>index</code></em> 35fields of struct <a class="link" href="vidioc-queryctrl.html#v4l2-querymenu" title="Table A.97. struct v4l2_querymenu">v4l2_querymenu</a> and call the 36<code class="constant">VIDIOC_QUERYMENU</code> ioctl with a pointer to this 37structure. The driver fills the rest of the structure or returns an 38<span class="errorcode">EINVAL</span> error code when the <em class="structfield"><code>id</code></em> or 39<em class="structfield"><code>index</code></em> is invalid. Menu items are enumerated 40by calling <code class="constant">VIDIOC_QUERYMENU</code> with successive 41<em class="structfield"><code>index</code></em> values from struct <a class="link" href="vidioc-queryctrl.html#v4l2-queryctrl" title="Table A.95. struct v4l2_queryctrl">v4l2_queryctrl</a> 42<em class="structfield"><code>minimum</code></em> to 43<em class="structfield"><code>maximum</code></em>, inclusive. Note that it is possible 44for <code class="constant">VIDIOC_QUERYMENU</code> to return an <span class="errorcode">EINVAL</span> error code for some 45indices between <em class="structfield"><code>minimum</code></em> and <em class="structfield"><code>maximum</code></em>. 46In that case that particular menu item is not supported by this driver. Also note that 47the <em class="structfield"><code>minimum</code></em> value is not necessarily 0.</p><p>See also the examples in <a class="xref" href="control.html" title="User Controls">the section called “User Controls”</a>.</p><div class="table"><a name="v4l2-queryctrl"></a><p class="title"><b>Table A.95. struct <span class="structname">v4l2_queryctrl</span></b></p><div class="table-contents"><table summary="struct v4l2_queryctrl" width="100%" border="0"><colgroup><col class="c1"><col class="c2"><col class="c3"></colgroup><tbody valign="top"><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>id</code></em></td><td valign="top">Identifies the control, set by the application. See 48<a class="xref" href="control.html#control-id" title="Table 1.1. Control IDs">Table 1.1, “Control IDs”</a> for predefined IDs. When the ID is ORed 49with V4L2_CTRL_FLAG_NEXT_CTRL the driver clears the flag and returns 50the first control with a higher ID. Drivers which do not support this 51flag yet always return an <span class="errorcode">EINVAL</span> error code.</td></tr><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>type</code></em></td><td valign="top">Type of control, see <a class="xref" href="vidioc-queryctrl.html#v4l2-ctrl-type" title="Table A.98. enum v4l2_ctrl_type">Table A.98, “enum v4l2_ctrl_type”</a>.</td></tr><tr><td valign="top">__u8</td><td valign="top"><em class="structfield"><code>name</code></em>[32]</td><td valign="top">Name of the control, a NUL-terminated ASCII 52string. This information is intended for the user.</td></tr><tr><td valign="top">__s32</td><td valign="top"><em class="structfield"><code>minimum</code></em></td><td valign="top">Minimum value, inclusive. This field gives a lower 53bound for the control. See enum <a class="link" href="vidioc-queryctrl.html#v4l2-ctrl-type" title="Table A.98. enum v4l2_ctrl_type">v4l2_ctrl_type</a> how the minimum value is to 54be used for each possible control type. Note that this a signed 32-bit value.</td></tr><tr><td valign="top">__s32</td><td valign="top"><em class="structfield"><code>maximum</code></em></td><td valign="top">Maximum value, inclusive. This field gives an upper 55bound for the control. See enum <a class="link" href="vidioc-queryctrl.html#v4l2-ctrl-type" title="Table A.98. enum v4l2_ctrl_type">v4l2_ctrl_type</a> how the maximum value is to 56be used for each possible control type. Note that this a signed 32-bit value.</td></tr><tr><td valign="top">__s32</td><td valign="top"><em class="structfield"><code>step</code></em></td><td valign="top"><p>This field gives a step size for the control. 57See enum <a class="link" href="vidioc-queryctrl.html#v4l2-ctrl-type" title="Table A.98. enum v4l2_ctrl_type">v4l2_ctrl_type</a> how the step value is to be used for each possible 58control type. Note that this an unsigned 32-bit value. 59</p><p>Generally drivers should not scale hardware 60control values. It may be necessary for example when the 61<em class="structfield"><code>name</code></em> or <em class="structfield"><code>id</code></em> imply 62a particular unit and the hardware actually accepts only multiples of 63said unit. If so, drivers must take care values are properly rounded 64when scaling, such that errors will not accumulate on repeated 65read-write cycles.</p><p>This field gives the smallest change of 66an integer control actually affecting hardware. Often the information 67is needed when the user can change controls by keyboard or GUI 68buttons, rather than a slider. When for example a hardware register 69accepts values 0-511 and the driver reports 0-65535, step should be 70128.</p><p>Note that although signed, the step value is supposed to 71be always positive.</p></td></tr><tr><td valign="top">__s32</td><td valign="top"><em class="structfield"><code>default_value</code></em></td><td valign="top">The default value of a 72<code class="constant">V4L2_CTRL_TYPE_INTEGER</code>, 73<code class="constant">_BOOLEAN</code>, <code class="constant">_BITMASK</code>, 74<code class="constant">_MENU</code> or <code class="constant">_INTEGER_MENU</code> control. 75Not valid for other types of controls. 76Note that drivers reset controls to their default value only when the 77driver is first loaded, never afterwards.</td></tr><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>flags</code></em></td><td valign="top">Control flags, see <a class="xref" href="vidioc-queryctrl.html#control-flags" title="Table A.99. Control Flags">Table A.99, “Control Flags”</a>.</td></tr><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>reserved</code></em>[2]</td><td valign="top">Reserved for future extensions. Drivers must set 78the array to zero.</td></tr></tbody></table></div></div><br class="table-break"><div class="table"><a name="v4l2-query-ext-ctrl"></a><p class="title"><b>Table A.96. struct <span class="structname">v4l2_query_ext_ctrl</span></b></p><div class="table-contents"><table summary="struct v4l2_query_ext_ctrl" width="100%" border="0"><colgroup><col class="c1"><col class="c2"><col class="c3"></colgroup><tbody valign="top"><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>id</code></em></td><td valign="top">Identifies the control, set by the application. See 79<a class="xref" href="control.html#control-id" title="Table 1.1. Control IDs">Table 1.1, “Control IDs”</a> for predefined IDs. When the ID is ORed 80with <code class="constant">V4L2_CTRL_FLAG_NEXT_CTRL</code> the driver clears the 81flag and returns the first non-compound control with a higher ID. When the 82ID is ORed with <code class="constant">V4L2_CTRL_FLAG_NEXT_COMPOUND</code> the driver 83clears the flag and returns the first compound control with a higher ID. 84Set both to get the first control (compound or not) with a higher ID.</td></tr><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>type</code></em></td><td valign="top">Type of control, see <a class="xref" href="vidioc-queryctrl.html#v4l2-ctrl-type" title="Table A.98. enum v4l2_ctrl_type">Table A.98, “enum v4l2_ctrl_type”</a>.</td></tr><tr><td valign="top">char</td><td valign="top"><em class="structfield"><code>name</code></em>[32]</td><td valign="top">Name of the control, a NUL-terminated ASCII 85string. This information is intended for the user.</td></tr><tr><td valign="top">__s64</td><td valign="top"><em class="structfield"><code>minimum</code></em></td><td valign="top">Minimum value, inclusive. This field gives a lower 86bound for the control. See enum <a class="link" href="vidioc-queryctrl.html#v4l2-ctrl-type" title="Table A.98. enum v4l2_ctrl_type">v4l2_ctrl_type</a> how the minimum value is to 87be used for each possible control type. Note that this a signed 64-bit value.</td></tr><tr><td valign="top">__s64</td><td valign="top"><em class="structfield"><code>maximum</code></em></td><td valign="top">Maximum value, inclusive. This field gives an upper 88bound for the control. See enum <a class="link" href="vidioc-queryctrl.html#v4l2-ctrl-type" title="Table A.98. enum v4l2_ctrl_type">v4l2_ctrl_type</a> how the maximum value is to 89be used for each possible control type. Note that this a signed 64-bit value.</td></tr><tr><td valign="top">__u64</td><td valign="top"><em class="structfield"><code>step</code></em></td><td valign="top"><p>This field gives a step size for the control. 90See enum <a class="link" href="vidioc-queryctrl.html#v4l2-ctrl-type" title="Table A.98. enum v4l2_ctrl_type">v4l2_ctrl_type</a> how the step value is to be used for each possible 91control type. Note that this an unsigned 64-bit value. 92</p><p>Generally drivers should not scale hardware 93control values. It may be necessary for example when the 94<em class="structfield"><code>name</code></em> or <em class="structfield"><code>id</code></em> imply 95a particular unit and the hardware actually accepts only multiples of 96said unit. If so, drivers must take care values are properly rounded 97when scaling, such that errors will not accumulate on repeated 98read-write cycles.</p><p>This field gives the smallest change of 99an integer control actually affecting hardware. Often the information 100is needed when the user can change controls by keyboard or GUI 101buttons, rather than a slider. When for example a hardware register 102accepts values 0-511 and the driver reports 0-65535, step should be 103128.</p></td></tr><tr><td valign="top">__s64</td><td valign="top"><em class="structfield"><code>default_value</code></em></td><td valign="top">The default value of a 104<code class="constant">V4L2_CTRL_TYPE_INTEGER</code>, <code class="constant">_INTEGER64</code>, 105<code class="constant">_BOOLEAN</code>, <code class="constant">_BITMASK</code>, 106<code class="constant">_MENU</code>, <code class="constant">_INTEGER_MENU</code>, 107<code class="constant">_U8</code> or <code class="constant">_U16</code> control. 108Not valid for other types of controls. 109Note that drivers reset controls to their default value only when the 110driver is first loaded, never afterwards. 111</td></tr><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>flags</code></em></td><td valign="top">Control flags, see <a class="xref" href="vidioc-queryctrl.html#control-flags" title="Table A.99. Control Flags">Table A.99, “Control Flags”</a>.</td></tr><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>elem_size</code></em></td><td valign="top">The size in bytes of a single element of the array. 112Given a char pointer <code class="constant">p</code> to a 3-dimensional array you can find the 113position of cell <code class="constant">(z, y, x)</code> as follows: 114<code class="constant">p + ((z * dims[1] + y) * dims[0] + x) * elem_size</code>. <em class="structfield"><code>elem_size</code></em> 115is always valid, also when the control isn't an array. For string controls 116<em class="structfield"><code>elem_size</code></em> is equal to <em class="structfield"><code>maximum + 1</code></em>. 117</td></tr><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>elems</code></em></td><td valign="top">The number of elements in the N-dimensional array. If this control 118is not an array, then <em class="structfield"><code>elems</code></em> is 1. The <em class="structfield"><code>elems</code></em> 119field can never be 0.</td></tr><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>nr_of_dims</code></em></td><td valign="top">The number of dimension in the N-dimensional array. If this control 120is not an array, then this field is 0.</td></tr><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>dims[V4L2_CTRL_MAX_DIMS]</code></em></td><td valign="top">The size of each dimension. The first <em class="structfield"><code>nr_of_dims</code></em> 121elements of this array must be non-zero, all remaining elements must be zero.</td></tr><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>reserved</code></em>[32]</td><td valign="top">Reserved for future extensions. Applications and drivers 122must set the array to zero.</td></tr></tbody></table></div></div><br class="table-break"><div class="table"><a name="v4l2-querymenu"></a><p class="title"><b>Table A.97. struct <span class="structname">v4l2_querymenu</span></b></p><div class="table-contents"><table summary="struct v4l2_querymenu" width="100%" border="0"><colgroup><col class="c1"><col class="c2"><col class="c3"><col></colgroup><tbody valign="top"><tr><td valign="top">__u32</td><td valign="top"> </td><td valign="top"><em class="structfield"><code>id</code></em></td><td valign="top">Identifies the control, set by the application 123from the respective struct <a class="link" href="vidioc-queryctrl.html#v4l2-queryctrl" title="Table A.95. struct v4l2_queryctrl">v4l2_queryctrl</a> 124<em class="structfield"><code>id</code></em>.</td></tr><tr><td valign="top">__u32</td><td valign="top"> </td><td valign="top"><em class="structfield"><code>index</code></em></td><td valign="top">Index of the menu item, starting at zero, set by 125 the application.</td></tr><tr><td valign="top">union</td><td valign="top"> </td><td valign="top"> </td><td valign="top"> </td></tr><tr><td valign="top"> </td><td valign="top">__u8</td><td valign="top"><em class="structfield"><code>name</code></em>[32]</td><td valign="top">Name of the menu item, a NUL-terminated ASCII 126string. This information is intended for the user. This field is valid 127for <code class="constant">V4L2_CTRL_FLAG_MENU</code> type controls.</td></tr><tr><td valign="top"> </td><td valign="top">__s64</td><td valign="top"><em class="structfield"><code>value</code></em></td><td valign="top"> 128 Value of the integer menu item. This field is valid for 129 <code class="constant">V4L2_CTRL_FLAG_INTEGER_MENU</code> type 130 controls. 131 </td></tr><tr><td valign="top">__u32</td><td valign="top"> </td><td valign="top"><em class="structfield"><code>reserved</code></em></td><td valign="top">Reserved for future extensions. Drivers must set 132the array to zero.</td></tr></tbody></table></div></div><br class="table-break"><div class="table"><a name="v4l2-ctrl-type"></a><p class="title"><b>Table A.98. enum v4l2_ctrl_type</b></p><div class="table-contents"><table summary="enum v4l2_ctrl_type" width="100%" border="0"><colgroup><col align="left"><col align="center"><col align="center"><col align="center"><col align="left"></colgroup><thead><tr><th align="left">Type</th><th align="center"><em class="structfield"><code>minimum</code></em></th><th align="center"><em class="structfield"><code>step</code></em></th><th align="center"><em class="structfield"><code>maximum</code></em></th><th align="left">Description</th></tr></thead><tbody valign="top"><tr><td align="left" valign="top"><code class="constant">V4L2_CTRL_TYPE_INTEGER</code></td><td align="center" valign="top">any</td><td align="center" valign="top">any</td><td align="center" valign="top">any</td><td align="left" valign="top">An integer-valued control ranging from minimum to 133maximum inclusive. The step value indicates the increment between 134values which are actually different on the hardware.</td></tr><tr><td align="left" valign="top"><code class="constant">V4L2_CTRL_TYPE_BOOLEAN</code></td><td align="center" valign="top">0</td><td align="center" valign="top">1</td><td align="center" valign="top">1</td><td align="left" valign="top">A boolean-valued control. Zero corresponds to 135"disabled", and one means "enabled".</td></tr><tr><td align="left" valign="top"><code class="constant">V4L2_CTRL_TYPE_MENU</code></td><td align="center" valign="top">≥ 0</td><td align="center" valign="top">1</td><td align="center" valign="top">N-1</td><td align="left" valign="top">The control has a menu of N choices. The names of 136the menu items can be enumerated with the 137<code class="constant">VIDIOC_QUERYMENU</code> ioctl.</td></tr><tr><td align="left" valign="top"><code class="constant">V4L2_CTRL_TYPE_INTEGER_MENU</code></td><td align="center" valign="top">≥ 0</td><td align="center" valign="top">1</td><td align="center" valign="top">N-1</td><td align="left" valign="top"> 138 The control has a menu of N choices. The values of the 139 menu items can be enumerated with the 140 <code class="constant">VIDIOC_QUERYMENU</code> ioctl. This is 141 similar to <code class="constant">V4L2_CTRL_TYPE_MENU</code> 142 except that instead of strings, the menu items are 143 signed 64-bit integers. 144 </td></tr><tr><td align="left" valign="top"><code class="constant">V4L2_CTRL_TYPE_BITMASK</code></td><td align="center" valign="top">0</td><td align="center" valign="top">n/a</td><td align="center" valign="top">any</td><td align="left" valign="top">A bitmask field. The maximum value is the set of bits that can 145be used, all other bits are to be 0. The maximum value is interpreted as a __u32, 146allowing the use of bit 31 in the bitmask.</td></tr><tr><td align="left" valign="top"><code class="constant">V4L2_CTRL_TYPE_BUTTON</code></td><td align="center" valign="top">0</td><td align="center" valign="top">0</td><td align="center" valign="top">0</td><td align="left" valign="top">A control which performs an action when set. 147Drivers must ignore the value passed with 148<code class="constant">VIDIOC_S_CTRL</code> and return an <span class="errorcode">EINVAL</span> error code on a 149<code class="constant">VIDIOC_G_CTRL</code> attempt.</td></tr><tr><td align="left" valign="top"><code class="constant">V4L2_CTRL_TYPE_INTEGER64</code></td><td align="center" valign="top">any</td><td align="center" valign="top">any</td><td align="center" valign="top">any</td><td align="left" valign="top">A 64-bit integer valued control. Minimum, maximum 150and step size cannot be queried using <code class="constant">VIDIOC_QUERYCTRL</code>. 151Only <code class="constant">VIDIOC_QUERY_EXT_CTRL</code> can retrieve the 64-bit 152min/max/step values, they should be interpreted as n/a when using 153<code class="constant">VIDIOC_QUERYCTRL</code>.</td></tr><tr><td align="left" valign="top"><code class="constant">V4L2_CTRL_TYPE_STRING</code></td><td align="center" valign="top">≥ 0</td><td align="center" valign="top">≥ 1</td><td align="center" valign="top">≥ 0</td><td align="left" valign="top">The minimum and maximum string lengths. The step size 154means that the string must be (minimum + N * step) characters long for 155N ≥ 0. These lengths do not include the terminating zero, so in order to 156pass a string of length 8 to <a class="link" href="vidioc-g-ext-ctrls.html" title="ioctl VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS, VIDIOC_TRY_EXT_CTRLS"><code class="constant">VIDIOC_S_EXT_CTRLS</code></a> you need to set the 157<em class="structfield"><code>size</code></em> field of struct <a class="link" href="vidioc-g-ext-ctrls.html#v4l2-ext-control" title="Table A.66. struct v4l2_ext_control">v4l2_ext_control</a> to 9. For <a class="link" href="vidioc-g-ext-ctrls.html" title="ioctl VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS, VIDIOC_TRY_EXT_CTRLS"><code class="constant">VIDIOC_G_EXT_CTRLS</code></a> you can 158set the <em class="structfield"><code>size</code></em> field to <em class="structfield"><code>maximum</code></em> + 1. 159Which character encoding is used will depend on the string control itself and 160should be part of the control documentation.</td></tr><tr><td align="left" valign="top"><code class="constant">V4L2_CTRL_TYPE_CTRL_CLASS</code></td><td align="center" valign="top">n/a</td><td align="center" valign="top">n/a</td><td align="center" valign="top">n/a</td><td align="left" valign="top">This is not a control. When 161<code class="constant">VIDIOC_QUERYCTRL</code> is called with a control ID 162equal to a control class code (see <a class="xref" href="vidioc-g-ext-ctrls.html#ctrl-class" title="Table A.68. Control classes">Table A.68, “Control classes”</a>) + 1, the 163ioctl returns the name of the control class and this control type. 164Older drivers which do not support this feature return an 165<span class="errorcode">EINVAL</span> error code.</td></tr><tr><td align="left" valign="top"><code class="constant">V4L2_CTRL_TYPE_U8</code></td><td align="center" valign="top">any</td><td align="center" valign="top">any</td><td align="center" valign="top">any</td><td align="left" valign="top">An unsigned 8-bit valued control ranging from minimum to 166maximum inclusive. The step value indicates the increment between 167values which are actually different on the hardware. 168</td></tr><tr><td align="left" valign="top"><code class="constant">V4L2_CTRL_TYPE_U16</code></td><td align="center" valign="top">any</td><td align="center" valign="top">any</td><td align="center" valign="top">any</td><td align="left" valign="top">An unsigned 16-bit valued control ranging from minimum to 169maximum inclusive. The step value indicates the increment between 170values which are actually different on the hardware. 171</td></tr></tbody></table></div></div><br class="table-break"><div class="table"><a name="control-flags"></a><p class="title"><b>Table A.99. Control Flags</b></p><div class="table-contents"><table summary="Control Flags" width="100%" border="0"><colgroup><col class="c1"><col class="c2"><col class="c3"></colgroup><tbody valign="top"><tr><td valign="top"><code class="constant">V4L2_CTRL_FLAG_DISABLED</code></td><td valign="top">0x0001</td><td valign="top">This control is permanently disabled and should be 172ignored by the application. Any attempt to change the control will 173result in an <span class="errorcode">EINVAL</span> error code.</td></tr><tr><td valign="top"><code class="constant">V4L2_CTRL_FLAG_GRABBED</code></td><td valign="top">0x0002</td><td valign="top">This control is temporarily unchangeable, for 174example because another application took over control of the 175respective resource. Such controls may be displayed specially in a 176user interface. Attempts to change the control may result in an 177<span class="errorcode">EBUSY</span> error code.</td></tr><tr><td valign="top"><code class="constant">V4L2_CTRL_FLAG_READ_ONLY</code></td><td valign="top">0x0004</td><td valign="top">This control is permanently readable only. Any 178attempt to change the control will result in an <span class="errorcode">EINVAL</span> error code.</td></tr><tr><td valign="top"><code class="constant">V4L2_CTRL_FLAG_UPDATE</code></td><td valign="top">0x0008</td><td valign="top">A hint that changing this control may affect the 179value of other controls within the same control class. Applications 180should update their user interface accordingly.</td></tr><tr><td valign="top"><code class="constant">V4L2_CTRL_FLAG_INACTIVE</code></td><td valign="top">0x0010</td><td valign="top">This control is not applicable to the current 181configuration and should be displayed accordingly in a user interface. 182For example the flag may be set on a MPEG audio level 2 bitrate 183control when MPEG audio encoding level 1 was selected with another 184control.</td></tr><tr><td valign="top"><code class="constant">V4L2_CTRL_FLAG_SLIDER</code></td><td valign="top">0x0020</td><td valign="top">A hint that this control is best represented as a 185slider-like element in a user interface.</td></tr><tr><td valign="top"><code class="constant">V4L2_CTRL_FLAG_WRITE_ONLY</code></td><td valign="top">0x0040</td><td valign="top">This control is permanently writable only. Any 186attempt to read the control will result in an <span class="errorcode">EACCES</span> error code error code. This 187flag is typically present for relative controls or action controls where 188writing a value will cause the device to carry out a given action 189(e. g. motor control) but no meaningful value can be returned.</td></tr><tr><td valign="top"><code class="constant">V4L2_CTRL_FLAG_VOLATILE</code></td><td valign="top">0x0080</td><td valign="top">This control is volatile, which means that the value of the control 190changes continuously. A typical example would be the current gain value if the device 191is in auto-gain mode. In such a case the hardware calculates the gain value based on 192the lighting conditions which can change over time. Note that setting a new value for 193a volatile control will have no effect and no <code class="constant">V4L2_EVENT_CTRL_CH_VALUE</code> 194will be sent, unless the <code class="constant">V4L2_CTRL_FLAG_EXECUTE_ON_WRITE</code> flag 195(see below) is also set. Otherwise the new value will just be ignored.</td></tr><tr><td valign="top"><code class="constant">V4L2_CTRL_FLAG_HAS_PAYLOAD</code></td><td valign="top">0x0100</td><td valign="top">This control has a pointer type, so its value has to be accessed 196using one of the pointer fields of struct <a class="link" href="vidioc-g-ext-ctrls.html#v4l2-ext-control" title="Table A.66. struct v4l2_ext_control">v4l2_ext_control</a>. This flag is set for controls 197that are an array, string, or have a compound type. In all cases you have to set a 198pointer to memory containing the payload of the control.</td></tr><tr><td valign="top"><code class="constant">V4L2_CTRL_FLAG_EXECUTE_ON_WRITE</code></td><td valign="top">0x0200</td><td valign="top">The value provided to the control will be propagated to the driver 199even if remains constant. This is required when the control represents an action 200on the hardware. For example: clearing an error flag or triggering the flash. All the 201controls of the type <code class="constant">V4L2_CTRL_TYPE_BUTTON</code> have this flag set.</td></tr></tbody></table></div></div><br class="table-break"></div><div class="refsect1"><a name="idp1116041484"></a><h2>Return Value</h2><p>On success <span class="returnvalue">0</span> is returned, on error <span class="returnvalue">-1</span> and the <code class="varname">errno</code> variable is set appropriately. The generic error codes are described at the <a class="link" href="gen_errors.html#gen-errors" title="Table 19.1. Generic error codes">Generic Error Codes</a> chapter.</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><span class="errorcode">EINVAL</span></span></dt><dd><p>The struct <a class="link" href="vidioc-queryctrl.html#v4l2-queryctrl" title="Table A.95. struct v4l2_queryctrl">v4l2_queryctrl</a> <em class="structfield"><code>id</code></em> 202is invalid. The struct <a class="link" href="vidioc-queryctrl.html#v4l2-querymenu" title="Table A.97. struct v4l2_querymenu">v4l2_querymenu</a> <em class="structfield"><code>id</code></em> is 203invalid or <em class="structfield"><code>index</code></em> is out of range (less than 204<em class="structfield"><code>minimum</code></em> or greater than <em class="structfield"><code>maximum</code></em>) 205or this particular menu item is not supported by the driver.</p></dd><dt><span class="term"><span class="errorcode">EACCES</span></span></dt><dd><p>An attempt was made to read a write-only control.</p></dd></dl></div></div><div class="footnotes"><br><hr style="width:100; text-align:left;margin-left: 0"><div id="ftn.idp1115934660" class="footnote"><p><a href="#idp1115934660" class="para"><sup class="para">[19] </sup></a><code class="constant">V4L2_CTRL_FLAG_DISABLED</code> was 206intended for two purposes: Drivers can skip predefined controls not 207supported by the hardware (although returning EINVAL would do as 208well), or disable predefined and private controls after hardware 209detection without the trouble of reordering control arrays and indices 210(EINVAL cannot be used to skip private controls because it would 211prematurely end the enumeration).</p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="vidioc-querycap.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="user-func.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="vidioc-query-dv-timings.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">ioctl VIDIOC_QUERYCAP </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> ioctl VIDIOC_QUERY_DV_TIMINGS</td></tr></table></div></body></html> 212