<?xml version="1.0" encoding="ANSI_X3.4-1968" standalone="no"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968" /><title>ioctl VIDIOC_QUERYCTRL, VIDIOC_QUERYMENU</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="index.html" title="LINUX MEDIA INFRASTRUCTURE API" /><link rel="up" href="apa.html" title="Appendix A. Function Reference" /><link rel="prev" href="re56.html" title="ioctl VIDIOC_QUERYCAP" /><link rel="next" href="re58.html" title="ioctl VIDIOC_QUERYSTD" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">ioctl VIDIOC_QUERYCTRL, VIDIOC_QUERYMENU</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="re56.html">Prev</a> </td><th width="60%" align="center">Appendix A. Function Reference</th><td width="20%" align="right"> <a accesskey="n" href="re58.html">Next</a></td></tr></table><hr /></div><div class="refentry" title="ioctl VIDIOC_QUERYCTRL, VIDIOC_QUERYMENU"><a id="vidioc-queryctrl"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>VIDIOC_QUERYCTRL, VIDIOC_QUERYMENU — Enumerate controls and menu control items</p></div><div class="refsynopsisdiv" title="Synopsis"><h2>Synopsis</h2><div class="funcsynopsis"><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" class="funcprototype-table"><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" summary="Function synopsis" cellspacing="0" cellpadding="0" class="funcprototype-table"><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" title="Arguments"><a id="id2922980"></a><h2>Arguments</h2><div class="variablelist"><dl><dt><span class="term"><em class="parameter"><code>fd</code></em></span></dt><dd><p>File descriptor returned by <a class="link" href="re64.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_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" title="Description"><a id="id2923048"></a><h2>Description</h2><p>To query the attributes of a control applications set the <em class="structfield"><code>id</code></em> field of a struct <a class="link" href="re57.html#v4l2-queryctrl" title="Table A.68. struct v4l2_queryctrl">v4l2_queryctrl</a> and call the <code class="constant">VIDIOC_QUERYCTRL</code> ioctl with a pointer to this structure. The driver fills the rest of the structure or returns an <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 <code class="constant">VIDIOC_QUERYCTRL</code> with successive <em class="structfield"><code>id</code></em> values starting from <code class="constant">V4L2_CID_BASE</code> up to and exclusive <code class="constant">V4L2_CID_BASE_LASTP1</code>. Drivers may return <span class="errorcode">EINVAL</span> 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 <code class="constant">V4L2_CID_PRIVATE_BASE</code> and incrementing <em class="structfield"><code>id</code></em> until the driver returns <span class="errorcode">EINVAL</span>.</p><p>In both cases, when the driver sets the <code class="constant">V4L2_CTRL_FLAG_DISABLED</code> flag in the <em class="structfield"><code>flags</code></em> field this control is permanently disabled and should be ignored by the application.<sup>[<a id="id2923140" href="#ftn.id2923140" class="footnote">25</a>]</sup></p><p>When the application ORs <em class="structfield"><code>id</code></em> with <code class="constant">V4L2_CTRL_FLAG_NEXT_CTRL</code> the driver returns the next supported control, or <span class="errorcode">EINVAL</span> if there is none. Drivers which do not support this flag yet always return <span class="errorcode">EINVAL</span>.</p><p>Additional information is required for menu controls: the names of the menu items. To query them applications set the <em class="structfield"><code>id</code></em> and <em class="structfield"><code>index</code></em> fields of struct <a class="link" href="re57.html#v4l2-querymenu" title="Table A.69. struct v4l2_querymenu">v4l2_querymenu</a> and call the <code class="constant">VIDIOC_QUERYMENU</code> ioctl with a pointer to this structure. The driver fills the rest of the structure or returns an <span class="errorcode">EINVAL</span> error code when the <em class="structfield"><code>id</code></em> or <em class="structfield"><code>index</code></em> is invalid. Menu items are enumerated by calling <code class="constant">VIDIOC_QUERYMENU</code> with successive <em class="structfield"><code>index</code></em> values from struct <a class="link" href="re57.html#v4l2-queryctrl" title="Table A.68. struct v4l2_queryctrl">v4l2_queryctrl</a> <em class="structfield"><code>minimum</code></em> (0) to <em class="structfield"><code>maximum</code></em>, inclusive.</p><p>See also the examples in <a class="xref" href="ch01s08.html" title="User Controls">the section called “User Controls”</a>.</p><div class="table"><a id="v4l2-queryctrl"></a><p class="title"><b>Table A.68. struct <span class="structname">v4l2_queryctrl</span></b></p><div class="table-contents"><table summary="struct v4l2_queryctrl" width="100%" border="0"><colgroup><col /><col /><col /></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 <a class="xref" href="ch01s08.html#control-id" title="Table 1.1. Control IDs">Table 1.1, “Control IDs”</a> 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 <span class="errorcode">EINVAL</span> error code.</td></tr><tr><td valign="top">enum <a class="link" href="re57.html#v4l2-ctrl-type" title="Table A.70. enum v4l2_ctrl_type">v4l2_ctrl_type</a></td><td valign="top"><em class="structfield"><code>type</code></em></td><td valign="top">Type of control, see <a class="xref" href="re57.html#v4l2-ctrl-type" title="Table A.70. enum v4l2_ctrl_type">Table A.70, “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 string. 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 bound for <code class="constant">V4L2_CTRL_TYPE_INTEGER</code> controls and the lowest valid index (always 0) for <code class="constant">V4L2_CTRL_TYPE_MENU</code> controls. For <code class="constant">V4L2_CTRL_TYPE_STRING</code> controls the minimum value gives the minimum length of the string. This length <span class="emphasis"><em>does not include the terminating zero</em></span>. It may not be valid for any other type of control, including <code class="constant">V4L2_CTRL_TYPE_INTEGER64</code> controls. Note that this is a signed 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 bound for <code class="constant">V4L2_CTRL_TYPE_INTEGER</code> controls and the highest valid index for <code class="constant">V4L2_CTRL_TYPE_MENU</code> controls. For <code class="constant">V4L2_CTRL_TYPE_STRING</code> controls the maximum value gives the maximum length of the string. This length <span class="emphasis"><em>does not include the terminating zero</em></span>. It may not be valid for any other type of control, including <code class="constant">V4L2_CTRL_TYPE_INTEGER64</code> controls. Note that this is a signed 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 <code class="constant">V4L2_CTRL_TYPE_INTEGER</code> controls. For <code class="constant">V4L2_CTRL_TYPE_STRING</code> 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 <code class="constant">V4L2_CTRL_TYPE_INTEGER64</code> controls.</p><p>Generally drivers should not scale hardware control values. It may be necessary for example when the <em class="structfield"><code>name</code></em> or <em class="structfield"><code>id</code></em> 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.</p><p>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.</p><p>Note that although signed, the step value is supposed to be 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 <code class="constant">V4L2_CTRL_TYPE_INTEGER</code>, <code class="constant">_BOOLEAN</code> or <code class="constant">_MENU</code> 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.</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="re57.html#control-flags" title="Table A.71. Control Flags">Table A.71, “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 the array to zero.</td></tr></tbody></table></div></div><br class="table-break" /><div class="table"><a id="v4l2-querymenu"></a><p class="title"><b>Table A.69. struct <span class="structname">v4l2_querymenu</span></b></p><div class="table-contents"><table summary="struct v4l2_querymenu" width="100%" border="0"><colgroup><col /><col /><col /></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 from the respective struct <a class="link" href="re57.html#v4l2-queryctrl" title="Table A.68. struct v4l2_queryctrl">v4l2_queryctrl</a> <em class="structfield"><code>id</code></em>.</td></tr><tr><td valign="top">__u32</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 the application.</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 menu item, a NUL-terminated ASCII string. This information is intended for the user.</td></tr><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>reserved</code></em></td><td valign="top">Reserved for future extensions. Drivers must set the array to zero.</td></tr></tbody></table></div></div><br class="table-break" /><div class="table"><a id="v4l2-ctrl-type"></a><p class="title"><b>Table A.70. 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 maximum inclusive. The step value indicates the increment between values 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 "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 the menu items can be enumerated with the <code class="constant">VIDIOC_QUERYMENU</code> ioctl.</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. Drivers must ignore the value passed with <code class="constant">VIDIOC_S_CTRL</code> and return an <span class="errorcode">EINVAL</span> error code on a <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">n/a</td><td align="center" valign="top">n/a</td><td align="center" valign="top">n/a</td><td align="left" valign="top">A 64-bit integer valued control. Minimum, maximum and step size cannot be queried.</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 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 <a class="link" href="re39.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 <em class="structfield"><code>size</code></em> field of struct <a class="link" href="re39.html#v4l2-ext-control" title="Table A.40. struct v4l2_ext_control">v4l2_ext_control</a> to 9. For <a class="link" href="re39.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 set the <em class="structfield"><code>size</code></em> field to <em class="structfield"><code>maximum</code></em> + 1. Which character encoding is used will depend on the string control itself and should 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 <code class="constant">VIDIOC_QUERYCTRL</code> is called with a control ID equal to a control class code (see <a class="xref" href="re39.html#ctrl-class" title="Table A.42. Control classes">Table A.42, “Control classes”</a>), the ioctl returns the name of the control class and this control type. Older drivers which do not support this feature return an <span class="errorcode">EINVAL</span> error code.</td></tr></tbody></table></div></div><br class="table-break" /><div class="table"><a id="control-flags"></a><p class="title"><b>Table A.71. Control Flags</b></p><div class="table-contents"><table summary="Control Flags" width="100%" border="0"><colgroup><col /><col /><col /></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 ignored by the application. Any attempt 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_GRABBED</code></td><td valign="top">0x0002</td><td valign="top">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 <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 attempt 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 value of other controls within the same control class. Applications should 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 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.</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 slider-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 attempt to read the control will result in an <span class="errorcode">EACCES</span> error code 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 (e. g. motor control) but no meaningful value can be returned.</td></tr></tbody></table></div></div><br class="table-break" /></div><div class="refsect1" title="Return Value"><a id="id2924360"></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:</p><div class="variablelist"><dl><dt><span class="term"><span class="errorcode">EINVAL</span></span></dt><dd><p>The struct <a class="link" href="re57.html#v4l2-queryctrl" title="Table A.68. struct v4l2_queryctrl">v4l2_queryctrl</a> <em class="structfield"><code>id</code></em> is invalid. The struct <a class="link" href="re57.html#v4l2-querymenu" title="Table A.69. struct v4l2_querymenu">v4l2_querymenu</a> <em class="structfield"><code>id</code></em> or <em class="structfield"><code>index</code></em> is invalid.</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 width="100" align="left" /><div class="footnote"><p><sup>[<a id="ftn.id2923140" href="#id2923140" class="para">25</a>] </sup><code class="constant">V4L2_CTRL_FLAG_DISABLED</code> 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).</p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="re56.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="apa.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="re58.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_QUERYSTD</td></tr></table></div></body></html>
