Documentation/DocBook/media/v4l/vidioc-queryctrl.xml

   1 <refentry id="vidioc-queryctrl">
   2   <refmeta>
   3     <refentrytitle>ioctl VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL, VIDIOC_QUERYMENU</refentrytitle>
   4     &manvol;
   5   </refmeta>
   6
   7   <refnamediv>
   8     <refname>VIDIOC_QUERYCTRL</refname>
   9     <refname>VIDIOC_QUERY_EXT_CTRL</refname>
  10     <refname>VIDIOC_QUERYMENU</refname>
  11     <refpurpose>Enumerate controls and menu control items</refpurpose>
  12   </refnamediv>
  13
  14   <refsynopsisdiv>
  15     <funcsynopsis>
  16       <funcprototype>
  17         <funcdef>int <function>ioctl</function></funcdef>
  18         <paramdef>int <parameter>fd</parameter></paramdef>
  19         <paramdef>int <parameter>request</parameter></paramdef>
  20         <paramdef>struct v4l2_queryctrl *<parameter>argp</parameter></paramdef>
  21       </funcprototype>
  22     </funcsynopsis>
  23     <funcsynopsis>
  24       <funcprototype>
  25         <funcdef>int <function>ioctl</function></funcdef>
  26         <paramdef>int <parameter>fd</parameter></paramdef>
  27         <paramdef>int <parameter>request</parameter></paramdef>
  28         <paramdef>struct v4l2_query_ext_ctrl *<parameter>argp</parameter></paramdef>
  29       </funcprototype>
  30     </funcsynopsis>
  31     <funcsynopsis>
  32       <funcprototype>
  33         <funcdef>int <function>ioctl</function></funcdef>
  34         <paramdef>int <parameter>fd</parameter></paramdef>
  35         <paramdef>int <parameter>request</parameter></paramdef>
  36         <paramdef>struct v4l2_querymenu *<parameter>argp</parameter></paramdef>
  37       </funcprototype>
  38     </funcsynopsis>
  39   </refsynopsisdiv>
  40
  41   <refsect1>
  42     <title>Arguments</title>
  43
  44     <variablelist>
  45       <varlistentry>
  46         <term><parameter>fd</parameter></term>
  47         <listitem>
  48           <para>&fd;</para>
  49         </listitem>
  50       </varlistentry>
  51       <varlistentry>
  52         <term><parameter>request</parameter></term>
  53         <listitem>
  54           <para>VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL, VIDIOC_QUERYMENU</para>
  55         </listitem>
  56       </varlistentry>
  57       <varlistentry>
  58         <term><parameter>argp</parameter></term>
  59         <listitem>
  60           <para></para>
  61         </listitem>
  62       </varlistentry>
  63     </variablelist>
  64   </refsect1>
  65
  66   <refsect1>
  67     <title>Description</title>
  68
  69     <para>To query the attributes of a control applications set the
  70 <structfield>id</structfield> field of a &v4l2-queryctrl; and call the
  71 <constant>VIDIOC_QUERYCTRL</constant> ioctl with a pointer to this
  72 structure. The driver fills the rest of the structure or returns an
  73 &EINVAL; when the <structfield>id</structfield> is invalid.</para>
  74
  75     <para>It is possible to enumerate controls by calling
  76 <constant>VIDIOC_QUERYCTRL</constant> with successive
  77 <structfield>id</structfield> values starting from
  78 <constant>V4L2_CID_BASE</constant> up to and exclusive
  79 <constant>V4L2_CID_LASTP1</constant>. Drivers may return
  80 <errorcode>EINVAL</errorcode> if a control in this range is not
  81 supported. Further applications can enumerate private controls, which
  82 are not defined in this specification, by starting at
  83 <constant>V4L2_CID_PRIVATE_BASE</constant> and incrementing
  84 <structfield>id</structfield> until the driver returns
  85 <errorcode>EINVAL</errorcode>.</para>
  86
  87     <para>In both cases, when the driver sets the
  88 <constant>V4L2_CTRL_FLAG_DISABLED</constant> flag in the
  89 <structfield>flags</structfield> field this control is permanently
  90 disabled and should be ignored by the application.<footnote>
  91         <para><constant>V4L2_CTRL_FLAG_DISABLED</constant> was
  92 intended for two purposes: Drivers can skip predefined controls not
  93 supported by the hardware (although returning EINVAL would do as
  94 well), or disable predefined and private controls after hardware
  95 detection without the trouble of reordering control arrays and indices
  96 (EINVAL cannot be used to skip private controls because it would
  97 prematurely end the enumeration).</para></footnote></para>
  98
  99     <para>When the application ORs <structfield>id</structfield> with
 100 <constant>V4L2_CTRL_FLAG_NEXT_CTRL</constant> the driver returns the
 101 next supported non-compound control, or <errorcode>EINVAL</errorcode>
 102 if there is none. In addition, the <constant>V4L2_CTRL_FLAG_NEXT_COMPOUND</constant>
 103 flag can be specified to enumerate all compound controls (i.e. controls
 104 with type &ge; <constant>V4L2_CTRL_COMPOUND_TYPES</constant> and/or array
 105 control, in other words controls that contain more than one value).
 106 Specify both <constant>V4L2_CTRL_FLAG_NEXT_CTRL</constant> and
 107 <constant>V4L2_CTRL_FLAG_NEXT_COMPOUND</constant> in order to enumerate
 108 all controls, compound or not. Drivers which do not support these flags yet
 109 always return <errorcode>EINVAL</errorcode>.</para>
 110
 111     <para>The <constant>VIDIOC_QUERY_EXT_CTRL</constant> ioctl was
 112 introduced in order to better support controls that can use compound
 113 types, and to expose additional control information that cannot be
 114 returned in &v4l2-queryctrl; since that structure is full.</para>
 115
 116     <para><constant>VIDIOC_QUERY_EXT_CTRL</constant> is used in the
 117 same way as <constant>VIDIOC_QUERYCTRL</constant>, except that the
 118 <structfield>reserved</structfield> array must be zeroed as well.</para>
 119
 120     <para>Additional information is required for menu controls: the
 121 names of the menu items. To query them applications set the
 122 <structfield>id</structfield> and <structfield>index</structfield>
 123 fields of &v4l2-querymenu; and call the
 124 <constant>VIDIOC_QUERYMENU</constant> ioctl with a pointer to this
 125 structure. The driver fills the rest of the structure or returns an
 126 &EINVAL; when the <structfield>id</structfield> or
 127 <structfield>index</structfield> is invalid. Menu items are enumerated
 128 by calling <constant>VIDIOC_QUERYMENU</constant> with successive
 129 <structfield>index</structfield> values from &v4l2-queryctrl;
 130 <structfield>minimum</structfield> to
 131 <structfield>maximum</structfield>, inclusive. Note that it is possible
 132 for <constant>VIDIOC_QUERYMENU</constant> to return an &EINVAL; for some
 133 indices between <structfield>minimum</structfield> and <structfield>maximum</structfield>.
 134 In that case that particular menu item is not supported by this driver. Also note that
 135 the <structfield>minimum</structfield> value is not necessarily 0.</para>
 136
 137     <para>See also the examples in <xref linkend="control" />.</para>
 138
 139     <table pgwide="1" frame="none" id="v4l2-queryctrl">
 140       <title>struct <structname>v4l2_queryctrl</structname></title>
 141       <tgroup cols="3">
 142         &cs-str;
 143         <tbody valign="top">
 144           <row>
 145             <entry>__u32</entry>
 146             <entry><structfield>id</structfield></entry>
 147             <entry>Identifies the control, set by the application. See
 148 <xref linkend="control-id" /> for predefined IDs. When the ID is ORed
 149 with V4L2_CTRL_FLAG_NEXT_CTRL the driver clears the flag and returns
 150 the first control with a higher ID. Drivers which do not support this
 151 flag yet always return an &EINVAL;.</entry>
 152           </row>
 153           <row>
 154             <entry>__u32</entry>
 155             <entry><structfield>type</structfield></entry>
 156             <entry>Type of control, see <xref
 157                 linkend="v4l2-ctrl-type" />.</entry>
 158           </row>
 159           <row>
 160             <entry>__u8</entry>
 161             <entry><structfield>name</structfield>[32]</entry>
 162             <entry>Name of the control, a NUL-terminated ASCII
 163 string. This information is intended for the user.</entry>
 164           </row>
 165           <row>
 166             <entry>__s32</entry>
 167             <entry><structfield>minimum</structfield></entry>
 168             <entry>Minimum value, inclusive. This field gives a lower
 169 bound for the control. See &v4l2-ctrl-type; how the minimum value is to
 170 be used for each possible control type. Note that this a signed 32-bit value.</entry>
 171           </row>
 172           <row>
 173             <entry>__s32</entry>
 174             <entry><structfield>maximum</structfield></entry>
 175             <entry>Maximum value, inclusive. This field gives an upper
 176 bound for the control. See &v4l2-ctrl-type; how the maximum value is to
 177 be used for each possible control type. Note that this a signed 32-bit value.</entry>
 178           </row>
 179           <row>
 180             <entry>__s32</entry>
 181             <entry><structfield>step</structfield></entry>
 182             <entry><para>This field gives a step size for the control.
 183 See &v4l2-ctrl-type; how the step value is to be used for each possible
 184 control type. Note that this an unsigned 32-bit value.
 185 </para><para>Generally drivers should not scale hardware
 186 control values. It may be necessary for example when the
 187 <structfield>name</structfield> or <structfield>id</structfield> imply
 188 a particular unit and the hardware actually accepts only multiples of
 189 said unit. If so, drivers must take care values are properly rounded
 190 when scaling, such that errors will not accumulate on repeated
 191 read-write cycles.</para><para>This field gives the smallest change of
 192 an integer control actually affecting hardware. Often the information
 193 is needed when the user can change controls by keyboard or GUI
 194 buttons, rather than a slider. When for example a hardware register
 195 accepts values 0-511 and the driver reports 0-65535, step should be
 196 128.</para><para>Note that although signed, the step value is supposed to
 197 be always positive.</para></entry>
 198           </row>
 199           <row>
 200             <entry>__s32</entry>
 201             <entry><structfield>default_value</structfield></entry>
 202             <entry>The default value of a
 203 <constant>V4L2_CTRL_TYPE_INTEGER</constant>,
 204 <constant>_BOOLEAN</constant>, <constant>_BITMASK</constant>,
 205 <constant>_MENU</constant> or <constant>_INTEGER_MENU</constant> control.
 206 Not valid for other types of controls.
 207 Note that drivers reset controls to their default value only when the
 208 driver is first loaded, never afterwards.</entry>
 209           </row>
 210           <row>
 211             <entry>__u32</entry>
 212             <entry><structfield>flags</structfield></entry>
 213             <entry>Control flags, see <xref
 214                 linkend="control-flags" />.</entry>
 215           </row>
 216           <row>
 217             <entry>__u32</entry>
 218             <entry><structfield>reserved</structfield>[2]</entry>
 219             <entry>Reserved for future extensions. Drivers must set
 220 the array to zero.</entry>
 221           </row>
 222         </tbody>
 223       </tgroup>
 224     </table>
 225
 226     <table pgwide="1" frame="none" id="v4l2-query-ext-ctrl">
 227       <title>struct <structname>v4l2_query_ext_ctrl</structname></title>
 228       <tgroup cols="3">
 229         &cs-str;
 230         <tbody valign="top">
 231           <row>
 232             <entry>__u32</entry>
 233             <entry><structfield>id</structfield></entry>
 234             <entry>Identifies the control, set by the application. See
 235 <xref linkend="control-id" /> for predefined IDs. When the ID is ORed
 236 with <constant>V4L2_CTRL_FLAG_NEXT_CTRL</constant> the driver clears the
 237 flag and returns the first non-compound control with a higher ID. When the
 238 ID is ORed with <constant>V4L2_CTRL_FLAG_NEXT_COMPOUND</constant> the driver
 239 clears the flag and returns the first compound control with a higher ID.
 240 Set both to get the first control (compound or not) with a higher ID.</entry>
 241           </row>
 242           <row>
 243             <entry>__u32</entry>
 244             <entry><structfield>type</structfield></entry>
 245             <entry>Type of control, see <xref
 246                 linkend="v4l2-ctrl-type" />.</entry>
 247           </row>
 248           <row>
 249             <entry>char</entry>
 250             <entry><structfield>name</structfield>[32]</entry>
 251             <entry>Name of the control, a NUL-terminated ASCII
 252 string. This information is intended for the user.</entry>
 253           </row>
 254           <row>
 255             <entry>__s64</entry>
 256             <entry><structfield>minimum</structfield></entry>
 257             <entry>Minimum value, inclusive. This field gives a lower
 258 bound for the control. See &v4l2-ctrl-type; how the minimum value is to
 259 be used for each possible control type. Note that this a signed 64-bit value.</entry>
 260           </row>
 261           <row>
 262             <entry>__s64</entry>
 263             <entry><structfield>maximum</structfield></entry>
 264             <entry>Maximum value, inclusive. This field gives an upper
 265 bound for the control. See &v4l2-ctrl-type; how the maximum value is to
 266 be used for each possible control type. Note that this a signed 64-bit value.</entry>
 267           </row>
 268           <row>
 269             <entry>__u64</entry>
 270             <entry><structfield>step</structfield></entry>
 271             <entry><para>This field gives a step size for the control.
 272 See &v4l2-ctrl-type; how the step value is to be used for each possible
 273 control type. Note that this an unsigned 64-bit value.
 274 </para><para>Generally drivers should not scale hardware
 275 control values. It may be necessary for example when the
 276 <structfield>name</structfield> or <structfield>id</structfield> imply
 277 a particular unit and the hardware actually accepts only multiples of
 278 said unit. If so, drivers must take care values are properly rounded
 279 when scaling, such that errors will not accumulate on repeated
 280 read-write cycles.</para><para>This field gives the smallest change of
 281 an integer control actually affecting hardware. Often the information
 282 is needed when the user can change controls by keyboard or GUI
 283 buttons, rather than a slider. When for example a hardware register
 284 accepts values 0-511 and the driver reports 0-65535, step should be
 285 128.</para></entry>
 286           </row>
 287           <row>
 288             <entry>__s64</entry>
 289             <entry><structfield>default_value</structfield></entry>
 290             <entry>The default value of a
 291 <constant>V4L2_CTRL_TYPE_INTEGER</constant>, <constant>_INTEGER64</constant>,
 292 <constant>_BOOLEAN</constant>, <constant>_BITMASK</constant>,
 293 <constant>_MENU</constant>, <constant>_INTEGER_MENU</constant>,
 294 <constant>_U8</constant> or <constant>_U16</constant> control.
 295 Not valid for other types of controls.
 296 Note that drivers reset controls to their default value only when the
 297 driver is first loaded, never afterwards.
 298 </entry>
 299           </row>
 300           <row>
 301             <entry>__u32</entry>
 302             <entry><structfield>flags</structfield></entry>
 303             <entry>Control flags, see <xref
 304                 linkend="control-flags" />.</entry>
 305           </row>
 306           <row>
 307             <entry>__u32</entry>
 308             <entry><structfield>elem_size</structfield></entry>
 309             <entry>The size in bytes of a single element of the array.
 310 Given a char pointer <constant>p</constant> to a 3-dimensional array you can find the
 311 position of cell <constant>(z, y, x)</constant> as follows:
 312 <constant>p + ((z * dims[1] + y) * dims[0] + x) * elem_size</constant>. <structfield>elem_size</structfield>
 313 is always valid, also when the control isn't an array. For string controls
 314 <structfield>elem_size</structfield> is equal to <structfield>maximum + 1</structfield>.
 315 </entry>
 316           </row>
 317           <row>
 318             <entry>__u32</entry>
 319             <entry><structfield>elems</structfield></entry>
 320             <entry>The number of elements in the N-dimensional array. If this control
 321 is not an array, then <structfield>elems</structfield> is 1. The <structfield>elems</structfield>
 322 field can never be 0.</entry>
 323           </row>
 324           <row>
 325             <entry>__u32</entry>
 326             <entry><structfield>nr_of_dims</structfield></entry>
 327             <entry>The number of dimension in the N-dimensional array. If this control
 328 is not an array, then this field is 0.</entry>
 329           </row>
 330           <row>
 331             <entry>__u32</entry>
 332             <entry><structfield>dims[V4L2_CTRL_MAX_DIMS]</structfield></entry>
 333             <entry>The size of each dimension. The first <structfield>nr_of_dims</structfield>
 334 elements of this array must be non-zero, all remaining elements must be zero.</entry>
 335           </row>
 336           <row>
 337             <entry>__u32</entry>
 338             <entry><structfield>reserved</structfield>[32]</entry>
 339             <entry>Reserved for future extensions. Applications and drivers
 340 must set the array to zero.</entry>
 341           </row>
 342         </tbody>
 343       </tgroup>
 344     </table>
 345
 346     <table pgwide="1" frame="none" id="v4l2-querymenu">
 347       <title>struct <structname>v4l2_querymenu</structname></title>
 348       <tgroup cols="4">
 349         &cs-str;
 350         <tbody valign="top">
 351           <row>
 352             <entry>__u32</entry>
 353             <entry></entry>
 354             <entry><structfield>id</structfield></entry>
 355             <entry>Identifies the control, set by the application
 356 from the respective &v4l2-queryctrl;
 357 <structfield>id</structfield>.</entry>
 358           </row>
 359           <row>
 360             <entry>__u32</entry>
 361             <entry></entry>
 362             <entry><structfield>index</structfield></entry>
 363             <entry>Index of the menu item, starting at zero, set by
 364             the application.</entry>
 365           </row>
 366           <row>
 367             <entry>union</entry>
 368             <entry></entry>
 369             <entry></entry>
 370             <entry></entry>
 371           </row>
 372           <row>
 373             <entry></entry>
 374             <entry>__u8</entry>
 375             <entry><structfield>name</structfield>[32]</entry>
 376             <entry>Name of the menu item, a NUL-terminated ASCII
 377 string. This information is intended for the user. This field is valid
 378 for <constant>V4L2_CTRL_FLAG_MENU</constant> type controls.</entry>
 379           </row>
 380           <row>
 381             <entry></entry>
 382             <entry>__s64</entry>
 383             <entry><structfield>value</structfield></entry>
 384             <entry>
 385               Value of the integer menu item. This field is valid for
 386               <constant>V4L2_CTRL_FLAG_INTEGER_MENU</constant> type
 387               controls.
 388             </entry>
 389           </row>
 390           <row>
 391             <entry>__u32</entry>
 392             <entry></entry>
 393             <entry><structfield>reserved</structfield></entry>
 394             <entry>Reserved for future extensions. Drivers must set
 395 the array to zero.</entry>
 396           </row>
 397         </tbody>
 398       </tgroup>
 399     </table>
 400
 401     <table pgwide="1" frame="none" id="v4l2-ctrl-type">
 402       <title>enum v4l2_ctrl_type</title>
 403       <tgroup cols="5" align="left">
 404         <colspec colwidth="30*" />
 405         <colspec colwidth="5*" align="center" />
 406         <colspec colwidth="5*" align="center" />
 407         <colspec colwidth="5*" align="center" />
 408         <colspec colwidth="55*" />
 409         <thead>
 410           <row>
 411             <entry>Type</entry>
 412             <entry><structfield>minimum</structfield></entry>
 413             <entry><structfield>step</structfield></entry>
 414             <entry><structfield>maximum</structfield></entry>
 415             <entry>Description</entry>
 416           </row>
 417         </thead>
 418         <tbody valign="top">
 419           <row>
 420             <entry><constant>V4L2_CTRL_TYPE_INTEGER</constant></entry>
 421             <entry>any</entry>
 422             <entry>any</entry>
 423             <entry>any</entry>
 424             <entry>An integer-valued control ranging from minimum to
 425 maximum inclusive. The step value indicates the increment between
 426 values.</entry>
 427           </row>
 428           <row>
 429             <entry><constant>V4L2_CTRL_TYPE_BOOLEAN</constant></entry>
 430             <entry>0</entry>
 431             <entry>1</entry>
 432             <entry>1</entry>
 433             <entry>A boolean-valued control. Zero corresponds to
 434 "disabled", and one means "enabled".</entry>
 435           </row>
 436           <row>
 437             <entry><constant>V4L2_CTRL_TYPE_MENU</constant></entry>
 438             <entry>&ge; 0</entry>
 439             <entry>1</entry>
 440             <entry>N-1</entry>
 441             <entry>The control has a menu of N choices. The names of
 442 the menu items can be enumerated with the
 443 <constant>VIDIOC_QUERYMENU</constant> ioctl.</entry>
 444           </row>
 445           <row>
 446             <entry><constant>V4L2_CTRL_TYPE_INTEGER_MENU</constant></entry>
 447             <entry>&ge; 0</entry>
 448             <entry>1</entry>
 449             <entry>N-1</entry>
 450             <entry>
 451               The control has a menu of N choices. The values of the
 452               menu items can be enumerated with the
 453               <constant>VIDIOC_QUERYMENU</constant> ioctl. This is
 454               similar to <constant>V4L2_CTRL_TYPE_MENU</constant>
 455               except that instead of strings, the menu items are
 456               signed 64-bit integers.
 457             </entry>
 458           </row>
 459           <row>
 460             <entry><constant>V4L2_CTRL_TYPE_BITMASK</constant></entry>
 461             <entry>0</entry>
 462             <entry>n/a</entry>
 463             <entry>any</entry>
 464             <entry>A bitmask field. The maximum value is the set of bits that can
 465 be used, all other bits are to be 0. The maximum value is interpreted as a __u32,
 466 allowing the use of bit 31 in the bitmask.</entry>
 467           </row>
 468           <row>
 469             <entry><constant>V4L2_CTRL_TYPE_BUTTON</constant></entry>
 470             <entry>0</entry>
 471             <entry>0</entry>
 472             <entry>0</entry>
 473             <entry>A control which performs an action when set.
 474 Drivers must ignore the value passed with
 475 <constant>VIDIOC_S_CTRL</constant> and return an &EINVAL; on a
 476 <constant>VIDIOC_G_CTRL</constant> attempt.</entry>
 477           </row>
 478           <row>
 479             <entry><constant>V4L2_CTRL_TYPE_INTEGER64</constant></entry>
 480             <entry>any</entry>
 481             <entry>any</entry>
 482             <entry>any</entry>
 483             <entry>A 64-bit integer valued control. Minimum, maximum
 484 and step size cannot be queried using <constant>VIDIOC_QUERYCTRL</constant>.
 485 Only <constant>VIDIOC_QUERY_EXT_CTRL</constant> can retrieve the 64-bit
 486 min/max/step values, they should be interpreted as n/a when using
 487 <constant>VIDIOC_QUERYCTRL</constant>.</entry>
 488           </row>
 489           <row>
 490             <entry><constant>V4L2_CTRL_TYPE_STRING</constant></entry>
 491             <entry>&ge; 0</entry>
 492             <entry>&ge; 1</entry>
 493             <entry>&ge; 0</entry>
 494             <entry>The minimum and maximum string lengths. The step size
 495 means that the string must be (minimum + N * step) characters long for
 496 N &ge; 0. These lengths do not include the terminating zero, so in order to
 497 pass a string of length 8 to &VIDIOC-S-EXT-CTRLS; you need to set the
 498 <structfield>size</structfield> field of &v4l2-ext-control; to 9. For &VIDIOC-G-EXT-CTRLS; you can
 499 set the <structfield>size</structfield> field to <structfield>maximum</structfield> + 1.
 500 Which character encoding is used will depend on the string control itself and
 501 should be part of the control documentation.</entry>
 502           </row>
 503           <row>
 504             <entry><constant>V4L2_CTRL_TYPE_CTRL_CLASS</constant></entry>
 505             <entry>n/a</entry>
 506             <entry>n/a</entry>
 507             <entry>n/a</entry>
 508             <entry>This is not a control. When
 509 <constant>VIDIOC_QUERYCTRL</constant> is called with a control ID
 510 equal to a control class code (see <xref linkend="ctrl-class" />) + 1, the
 511 ioctl returns the name of the control class and this control type.
 512 Older drivers which do not support this feature return an
 513 &EINVAL;.</entry>
 514           </row>
 515           <row>
 516             <entry><constant>V4L2_CTRL_TYPE_U8</constant></entry>
 517             <entry>any</entry>
 518             <entry>any</entry>
 519             <entry>any</entry>
 520             <entry>An unsigned 8-bit valued control ranging from minimum to
 521 maximum inclusive. The step value indicates the increment between
 522 values.
 523 </entry>
 524           </row>
 525           <row>
 526             <entry><constant>V4L2_CTRL_TYPE_U16</constant></entry>
 527             <entry>any</entry>
 528             <entry>any</entry>
 529             <entry>any</entry>
 530             <entry>An unsigned 16-bit valued control ranging from minimum to
 531 maximum inclusive. The step value indicates the increment between
 532 values.
 533 </entry>
 534           </row>
 535           <row>
 536             <entry><constant>V4L2_CTRL_TYPE_U32</constant></entry>
 537             <entry>any</entry>
 538             <entry>any</entry>
 539             <entry>any</entry>
 540             <entry>An unsigned 32-bit valued control ranging from minimum to
 541 maximum inclusive. The step value indicates the increment between
 542 values.
 543 </entry>
 544           </row>
 545         </tbody>
 546       </tgroup>
 547     </table>
 548
 549     <table pgwide="1" frame="none" id="control-flags">
 550       <title>Control Flags</title>
 551       <tgroup cols="3">
 552         &cs-def;
 553         <tbody valign="top">
 554           <row>
 555             <entry><constant>V4L2_CTRL_FLAG_DISABLED</constant></entry>
 556             <entry>0x0001</entry>
 557             <entry>This control is permanently disabled and should be
 558 ignored by the application. Any attempt to change the control will
 559 result in an &EINVAL;.</entry>
 560           </row>
 561           <row>
 562             <entry><constant>V4L2_CTRL_FLAG_GRABBED</constant></entry>
 563             <entry>0x0002</entry>
 564             <entry>This control is temporarily unchangeable, for
 565 example because another application took over control of the
 566 respective resource. Such controls may be displayed specially in a
 567 user interface. Attempts to change the control may result in an
 568 &EBUSY;.</entry>
 569           </row>
 570           <row>
 571             <entry><constant>V4L2_CTRL_FLAG_READ_ONLY</constant></entry>
 572             <entry>0x0004</entry>
 573             <entry>This control is permanently readable only. Any
 574 attempt to change the control will result in an &EINVAL;.</entry>
 575           </row>
 576           <row>
 577             <entry><constant>V4L2_CTRL_FLAG_UPDATE</constant></entry>
 578             <entry>0x0008</entry>
 579             <entry>A hint that changing this control may affect the
 580 value of other controls within the same control class. Applications
 581 should update their user interface accordingly.</entry>
 582           </row>
 583           <row>
 584             <entry><constant>V4L2_CTRL_FLAG_INACTIVE</constant></entry>
 585             <entry>0x0010</entry>
 586             <entry>This control is not applicable to the current
 587 configuration and should be displayed accordingly in a user interface.
 588 For example the flag may be set on a MPEG audio level 2 bitrate
 589 control when MPEG audio encoding level 1 was selected with another
 590 control.</entry>
 591           </row>
 592           <row>
 593             <entry><constant>V4L2_CTRL_FLAG_SLIDER</constant></entry>
 594             <entry>0x0020</entry>
 595             <entry>A hint that this control is best represented as a
 596 slider-like element in a user interface.</entry>
 597           </row>
 598           <row>
 599             <entry><constant>V4L2_CTRL_FLAG_WRITE_ONLY</constant></entry>
 600             <entry>0x0040</entry>
 601             <entry>This control is permanently writable only. Any
 602 attempt to read the control will result in an &EACCES; error code. This
 603 flag is typically present for relative controls or action controls where
 604 writing a value will cause the device to carry out a given action
 605 (&eg; motor control) but no meaningful value can be returned.</entry>
 606           </row>
 607           <row>
 608             <entry><constant>V4L2_CTRL_FLAG_VOLATILE</constant></entry>
 609             <entry>0x0080</entry>
 610             <entry>This control is volatile, which means that the value of the control
 611 changes continuously. A typical example would be the current gain value if the device
 612 is in auto-gain mode. In such a case the hardware calculates the gain value based on
 613 the lighting conditions which can change over time. Note that setting a new value for
 614 a volatile control will have no effect and no <constant>V4L2_EVENT_CTRL_CH_VALUE</constant>
 615 will be sent, unless the <constant>V4L2_CTRL_FLAG_EXECUTE_ON_WRITE</constant> flag
 616 (see below) is also set. Otherwise the new value will just be ignored.</entry>
 617           </row>
 618           <row>
 619             <entry><constant>V4L2_CTRL_FLAG_HAS_PAYLOAD</constant></entry>
 620             <entry>0x0100</entry>
 621             <entry>This control has a pointer type, so its value has to be accessed
 622 using one of the pointer fields of &v4l2-ext-control;. This flag is set for controls
 623 that are an array, string, or have a compound type. In all cases you have to set a
 624 pointer to memory containing the payload of the control.</entry>
 625           </row>
 626           <row>
 627             <entry><constant>V4L2_CTRL_FLAG_EXECUTE_ON_WRITE</constant></entry>
 628             <entry>0x0200</entry>
 629             <entry>The value provided to the control will be propagated to the driver
 630 even if it remains constant. This is required when the control represents an action
 631 on the hardware. For example: clearing an error flag or triggering the flash. All the
 632 controls of the type <constant>V4L2_CTRL_TYPE_BUTTON</constant> have this flag set.</entry>
 633           </row>
 634         </tbody>
 635       </tgroup>
 636     </table>
 637   </refsect1>
 638
 639   <refsect1>
 640     &return-value;
 641
 642     <variablelist>
 643       <varlistentry>
 644         <term><errorcode>EINVAL</errorcode></term>
 645         <listitem>
 646           <para>The &v4l2-queryctrl; <structfield>id</structfield>
 647 is invalid. The &v4l2-querymenu; <structfield>id</structfield> is
 648 invalid or <structfield>index</structfield> is out of range (less than
 649 <structfield>minimum</structfield> or greater than <structfield>maximum</structfield>)
 650 or this particular menu item is not supported by the driver.</para>
 651         </listitem>
 652       </varlistentry>
 653       <varlistentry>
 654         <term><errorcode>EACCES</errorcode></term>
 655         <listitem>
 656           <para>An attempt was made to read a write-only control.</para>
 657         </listitem>
 658       </varlistentry>
 659     </variablelist>
 660   </refsect1>
 661 </refentry>