Documentation/DocBook/media/v4l/vidioc-g-ext-ctrls.xml

   1 <refentry id="vidioc-g-ext-ctrls">
   2   <refmeta>
   3     <refentrytitle>ioctl VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS,
   4 VIDIOC_TRY_EXT_CTRLS</refentrytitle>
   5     &manvol;
   6   </refmeta>
   7
   8   <refnamediv>
   9     <refname>VIDIOC_G_EXT_CTRLS</refname>
  10     <refname>VIDIOC_S_EXT_CTRLS</refname>
  11     <refname>VIDIOC_TRY_EXT_CTRLS</refname>
  12     <refpurpose>Get or set the value of several controls, try control
  13 values</refpurpose>
  14   </refnamediv>
  15
  16   <refsynopsisdiv>
  17     <funcsynopsis>
  18       <funcprototype>
  19         <funcdef>int <function>ioctl</function></funcdef>
  20         <paramdef>int <parameter>fd</parameter></paramdef>
  21         <paramdef>int <parameter>request</parameter></paramdef>
  22         <paramdef>struct v4l2_ext_controls
  23 *<parameter>argp</parameter></paramdef>
  24       </funcprototype>
  25     </funcsynopsis>
  26   </refsynopsisdiv>
  27
  28   <refsect1>
  29     <title>Arguments</title>
  30
  31     <variablelist>
  32       <varlistentry>
  33         <term><parameter>fd</parameter></term>
  34         <listitem>
  35           <para>&fd;</para>
  36         </listitem>
  37       </varlistentry>
  38       <varlistentry>
  39         <term><parameter>request</parameter></term>
  40         <listitem>
  41           <para>VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS,
  42 VIDIOC_TRY_EXT_CTRLS</para>
  43         </listitem>
  44       </varlistentry>
  45       <varlistentry>
  46         <term><parameter>argp</parameter></term>
  47         <listitem>
  48           <para></para>
  49         </listitem>
  50       </varlistentry>
  51     </variablelist>
  52   </refsect1>
  53
  54   <refsect1>
  55     <title>Description</title>
  56
  57     <para>These ioctls allow the caller to get or set multiple
  58 controls atomically. Control IDs are grouped into control classes (see
  59 <xref linkend="ctrl-class" />) and all controls in the control array
  60 must belong to the same control class.</para>
  61
  62     <para>Applications must always fill in the
  63 <structfield>count</structfield>,
  64 <structfield>ctrl_class</structfield>,
  65 <structfield>controls</structfield> and
  66 <structfield>reserved</structfield> fields of &v4l2-ext-controls;, and
  67 initialize the &v4l2-ext-control; array pointed to by the
  68 <structfield>controls</structfield> fields.</para>
  69
  70     <para>To get the current value of a set of controls applications
  71 initialize the <structfield>id</structfield>,
  72 <structfield>size</structfield> and <structfield>reserved2</structfield> fields
  73 of each &v4l2-ext-control; and call the
  74 <constant>VIDIOC_G_EXT_CTRLS</constant> ioctl. String controls controls
  75 must also set the <structfield>string</structfield> field.</para>
  76
  77     <para>If the <structfield>size</structfield> is too small to
  78 receive the control result (only relevant for pointer-type controls
  79 like strings), then the driver will set <structfield>size</structfield>
  80 to a valid value and return an &ENOSPC;. You should re-allocate the
  81 string memory to this new size and try again. It is possible that the
  82 same issue occurs again if the string has grown in the meantime. It is
  83 recommended to call &VIDIOC-QUERYCTRL; first and use
  84 <structfield>maximum</structfield>+1 as the new <structfield>size</structfield>
  85 value. It is guaranteed that that is sufficient memory.
  86 </para>
  87
  88     <para>To change the value of a set of controls applications
  89 initialize the <structfield>id</structfield>, <structfield>size</structfield>,
  90 <structfield>reserved2</structfield> and
  91 <structfield>value/string</structfield> fields of each &v4l2-ext-control; and
  92 call the <constant>VIDIOC_S_EXT_CTRLS</constant> ioctl. The controls
  93 will only be set if <emphasis>all</emphasis> control values are
  94 valid.</para>
  95
  96     <para>To check if a set of controls have correct values applications
  97 initialize the <structfield>id</structfield>, <structfield>size</structfield>,
  98 <structfield>reserved2</structfield> and
  99 <structfield>value/string</structfield> fields of each &v4l2-ext-control; and
 100 call the <constant>VIDIOC_TRY_EXT_CTRLS</constant> ioctl. It is up to
 101 the driver whether wrong values are automatically adjusted to a valid
 102 value or if an error is returned.</para>
 103
 104     <para>When the <structfield>id</structfield> or
 105 <structfield>ctrl_class</structfield> is invalid drivers return an
 106 &EINVAL;. When the value is out of bounds drivers can choose to take
 107 the closest valid value or return an &ERANGE;, whatever seems more
 108 appropriate. In the first case the new value is set in
 109 &v4l2-ext-control;.</para>
 110
 111     <para>The driver will only set/get these controls if all control
 112 values are correct. This prevents the situation where only some of the
 113 controls were set/get. Only low-level errors (&eg; a failed i2c
 114 command) can still cause this situation.</para>
 115
 116     <table pgwide="1" frame="none" id="v4l2-ext-control">
 117       <title>struct <structname>v4l2_ext_control</structname></title>
 118       <tgroup cols="4">
 119         &cs-ustr;
 120         <tbody valign="top">
 121           <row>
 122             <entry>__u32</entry>
 123             <entry><structfield>id</structfield></entry>
 124             <entry></entry>
 125             <entry>Identifies the control, set by the
 126 application.</entry>
 127           </row>
 128           <row>
 129             <entry>__u32</entry>
 130             <entry><structfield>size</structfield></entry>
 131             <entry></entry>
 132             <entry>The total size in bytes of the payload of this
 133 control. This is normally 0, but for pointer controls this should be
 134 set to the size of the memory containing the payload, or that will
 135 receive the payload. If <constant>VIDIOC_G_EXT_CTRLS</constant> finds
 136 that this value is less than is required to store
 137 the payload result, then it is set to a value large enough to store the
 138 payload result and ENOSPC is returned. Note that for string controls
 139 this <structfield>size</structfield> field should not be confused with the length of the string.
 140 This field refers to the size of the memory that contains the string.
 141 The actual <emphasis>length</emphasis> of the string may well be much smaller.
 142 </entry>
 143           </row>
 144           <row>
 145             <entry>__u32</entry>
 146             <entry><structfield>reserved2</structfield>[1]</entry>
 147             <entry></entry>
 148             <entry>Reserved for future extensions. Drivers and
 149 applications must set the array to zero.</entry>
 150           </row>
 151           <row>
 152             <entry>union</entry>
 153             <entry>(anonymous)</entry>
 154           </row>
 155           <row>
 156             <entry></entry>
 157             <entry>__s32</entry>
 158             <entry><structfield>value</structfield></entry>
 159             <entry>New value or current value.</entry>
 160           </row>
 161           <row>
 162             <entry></entry>
 163             <entry>__s64</entry>
 164             <entry><structfield>value64</structfield></entry>
 165             <entry>New value or current value.</entry>
 166           </row>
 167           <row>
 168             <entry></entry>
 169             <entry>char *</entry>
 170             <entry><structfield>string</structfield></entry>
 171             <entry>A pointer to a string.</entry>
 172           </row>
 173         </tbody>
 174       </tgroup>
 175     </table>
 176
 177     <table pgwide="1" frame="none" id="v4l2-ext-controls">
 178       <title>struct <structname>v4l2_ext_controls</structname></title>
 179       <tgroup cols="3">
 180         &cs-str;
 181         <tbody valign="top">
 182           <row>
 183             <entry>__u32</entry>
 184             <entry><structfield>ctrl_class</structfield></entry>
 185             <entry>The control class to which all controls belong, see
 186 <xref linkend="ctrl-class" />. Drivers that use a kernel framework for handling
 187 controls will also accept a value of 0 here, meaning that the controls can
 188 belong to any control class. Whether drivers support this can be tested by setting
 189 <structfield>ctrl_class</structfield> to 0 and calling <constant>VIDIOC_TRY_EXT_CTRLS</constant>
 190 with a <structfield>count</structfield> of 0. If that succeeds, then the driver
 191 supports this feature.</entry>
 192           </row>
 193           <row>
 194             <entry>__u32</entry>
 195             <entry><structfield>count</structfield></entry>
 196             <entry>The number of controls in the controls array. May
 197 also be zero.</entry>
 198           </row>
 199           <row>
 200             <entry>__u32</entry>
 201             <entry><structfield>error_idx</structfield></entry>
 202             <entry>Set by the driver in case of an error. If it is equal
 203 to <structfield>count</structfield>, then no actual changes were made to
 204 controls. In other words, the error was not associated with setting a particular
 205 control. If it is another value, then only the controls up to <structfield>error_idx-1</structfield>
 206 were modified and control <structfield>error_idx</structfield> is the one that
 207 caused the error. The <structfield>error_idx</structfield> value is undefined
 208 if the ioctl returned 0 (success).</entry>
 209           </row>
 210           <row>
 211             <entry>__u32</entry>
 212             <entry><structfield>reserved</structfield>[2]</entry>
 213             <entry>Reserved for future extensions. Drivers and
 214 applications must set the array to zero.</entry>
 215           </row>
 216           <row>
 217             <entry>&v4l2-ext-control; *</entry>
 218             <entry><structfield>controls</structfield></entry>
 219             <entry>Pointer to an array of
 220 <structfield>count</structfield> v4l2_ext_control structures. Ignored
 221 if <structfield>count</structfield> equals zero.</entry>
 222           </row>
 223         </tbody>
 224       </tgroup>
 225     </table>
 226
 227     <table pgwide="1" frame="none" id="ctrl-class">
 228       <title>Control classes</title>
 229       <tgroup cols="3">
 230         &cs-def;
 231         <tbody valign="top">
 232           <row>
 233             <entry><constant>V4L2_CTRL_CLASS_USER</constant></entry>
 234             <entry>0x980000</entry>
 235             <entry>The class containing user controls. These controls
 236 are described in <xref linkend="control" />. All controls that can be set
 237 using the &VIDIOC-S-CTRL; and &VIDIOC-G-CTRL; ioctl belong to this
 238 class.</entry>
 239           </row>
 240           <row>
 241             <entry><constant>V4L2_CTRL_CLASS_MPEG</constant></entry>
 242             <entry>0x990000</entry>
 243             <entry>The class containing MPEG compression controls.
 244 These controls are described in <xref
 245                 linkend="mpeg-controls" />.</entry>
 246           </row>
 247           <row>
 248             <entry><constant>V4L2_CTRL_CLASS_CAMERA</constant></entry>
 249             <entry>0x9a0000</entry>
 250             <entry>The class containing camera controls.
 251 These controls are described in <xref
 252                 linkend="camera-controls" />.</entry>
 253           </row>
 254           <row>
 255             <entry><constant>V4L2_CTRL_CLASS_FM_TX</constant></entry>
 256             <entry>0x9b0000</entry>
 257             <entry>The class containing FM Transmitter (FM TX) controls.
 258 These controls are described in <xref
 259                 linkend="fm-tx-controls" />.</entry>
 260           </row>
 261           <row>
 262             <entry><constant>V4L2_CTRL_CLASS_FLASH</constant></entry>
 263             <entry>0x9c0000</entry>
 264             <entry>The class containing flash device controls.
 265 These controls are described in <xref
 266                 linkend="flash-controls" />.</entry>
 267           </row>
 268         </tbody>
 269       </tgroup>
 270     </table>
 271
 272   </refsect1>
 273
 274   <refsect1>
 275     &return-value;
 276
 277     <variablelist>
 278       <varlistentry>
 279         <term><errorcode>EINVAL</errorcode></term>
 280         <listitem>
 281           <para>The &v4l2-ext-control; <structfield>id</structfield>
 282 is invalid or the &v4l2-ext-controls;
 283 <structfield>ctrl_class</structfield> is invalid. This error code is
 284 also returned by the <constant>VIDIOC_S_EXT_CTRLS</constant> and
 285 <constant>VIDIOC_TRY_EXT_CTRLS</constant> ioctls if two or more
 286 control values are in conflict.</para>
 287         </listitem>
 288       </varlistentry>
 289       <varlistentry>
 290         <term><errorcode>ERANGE</errorcode></term>
 291         <listitem>
 292           <para>The &v4l2-ext-control; <structfield>value</structfield>
 293 is out of bounds.</para>
 294         </listitem>
 295       </varlistentry>
 296       <varlistentry>
 297         <term><errorcode>EBUSY</errorcode></term>
 298         <listitem>
 299           <para>The control is temporarily not changeable, possibly
 300 because another applications took over control of the device function
 301 this control belongs to.</para>
 302         </listitem>
 303       </varlistentry>
 304       <varlistentry>
 305         <term><errorcode>ENOSPC</errorcode></term>
 306         <listitem>
 307           <para>The space reserved for the control's payload is insufficient.
 308 The field <structfield>size</structfield> is set to a value that is enough
 309 to store the payload and this error code is returned.</para>
 310         </listitem>
 311       </varlistentry>
 312       <varlistentry>
 313         <term><errorcode>EACCES</errorcode></term>
 314         <listitem>
 315           <para>Attempt to try or set a read-only control or to get a
 316           write-only control.</para>
 317         </listitem>
 318       </varlistentry>
 319     </variablelist>
 320   </refsect1>
 321 </refentry>
 322