1<refentry id="vidioc-queryctrl"> 2 <refmeta> 3 <refentrytitle>ioctl VIDIOC_QUERYCTRL, VIDIOC_QUERYMENU</refentrytitle> 4 &manvol; 5 </refmeta> 6 7 <refnamediv> 8 <refname>VIDIOC_QUERYCTRL</refname> 9 <refname>VIDIOC_QUERYMENU</refname> 10 <refpurpose>Enumerate controls and menu control items</refpurpose> 11 </refnamediv> 12 13 <refsynopsisdiv> 14 <funcsynopsis> 15 <funcprototype> 16 <funcdef>int <function>ioctl</function></funcdef> 17 <paramdef>int <parameter>fd</parameter></paramdef> 18 <paramdef>int <parameter>request</parameter></paramdef> 19 <paramdef>struct v4l2_queryctrl *<parameter>argp</parameter></paramdef> 20 </funcprototype> 21 </funcsynopsis> 22 <funcsynopsis> 23 <funcprototype> 24 <funcdef>int <function>ioctl</function></funcdef> 25 <paramdef>int <parameter>fd</parameter></paramdef> 26 <paramdef>int <parameter>request</parameter></paramdef> 27 <paramdef>struct v4l2_querymenu *<parameter>argp</parameter></paramdef> 28 </funcprototype> 29 </funcsynopsis> 30 </refsynopsisdiv> 31 32 <refsect1> 33 <title>Arguments</title> 34 35 <variablelist> 36 <varlistentry> 37 <term><parameter>fd</parameter></term> 38 <listitem> 39 <para>&fd;</para> 40 </listitem> 41 </varlistentry> 42 <varlistentry> 43 <term><parameter>request</parameter></term> 44 <listitem> 45 <para>VIDIOC_QUERYCTRL, VIDIOC_QUERYMENU</para> 46 </listitem> 47 </varlistentry> 48 <varlistentry> 49 <term><parameter>argp</parameter></term> 50 <listitem> 51 <para></para> 52 </listitem> 53 </varlistentry> 54 </variablelist> 55 </refsect1> 56 57 <refsect1> 58 <title>Description</title> 59 60 <para>To query the attributes of a control applications set the 61<structfield>id</structfield> field of a &v4l2-queryctrl; and call the 62<constant>VIDIOC_QUERYCTRL</constant> ioctl with a pointer to this 63structure. The driver fills the rest of the structure or returns an 64&EINVAL; when the <structfield>id</structfield> is invalid.</para> 65 66 <para>It is possible to enumerate controls by calling 67<constant>VIDIOC_QUERYCTRL</constant> with successive 68<structfield>id</structfield> values starting from 69<constant>V4L2_CID_BASE</constant> up to and exclusive 70<constant>V4L2_CID_BASE_LASTP1</constant>. Drivers may return 71<errorcode>EINVAL</errorcode> if a control in this range is not 72supported. Further applications can enumerate private controls, which 73are not defined in this specification, by starting at 74<constant>V4L2_CID_PRIVATE_BASE</constant> and incrementing 75<structfield>id</structfield> until the driver returns 76<errorcode>EINVAL</errorcode>.</para> 77 78 <para>In both cases, when the driver sets the 79<constant>V4L2_CTRL_FLAG_DISABLED</constant> flag in the 80<structfield>flags</structfield> field this control is permanently 81disabled and should be ignored by the application.<footnote> 82 <para><constant>V4L2_CTRL_FLAG_DISABLED</constant> was 83intended for two purposes: Drivers can skip predefined controls not 84supported by the hardware (although returning EINVAL would do as 85well), or disable predefined and private controls after hardware 86detection without the trouble of reordering control arrays and indices 87(EINVAL cannot be used to skip private controls because it would 88prematurely end the enumeration).</para></footnote></para> 89 90 <para>When the application ORs <structfield>id</structfield> with 91<constant>V4L2_CTRL_FLAG_NEXT_CTRL</constant> the driver returns the 92next supported control, or <errorcode>EINVAL</errorcode> if there is 93none. Drivers which do not support this flag yet always return 94<errorcode>EINVAL</errorcode>.</para> 95 96 <para>Additional information is required for menu controls: the 97names of the menu items. To query them applications set the 98<structfield>id</structfield> and <structfield>index</structfield> 99fields of &v4l2-querymenu; and call the 100<constant>VIDIOC_QUERYMENU</constant> ioctl with a pointer to this 101structure. The driver fills the rest of the structure or returns an 102&EINVAL; when the <structfield>id</structfield> or 103<structfield>index</structfield> is invalid. Menu items are enumerated 104by calling <constant>VIDIOC_QUERYMENU</constant> with successive 105<structfield>index</structfield> values from &v4l2-queryctrl; 106<structfield>minimum</structfield> (0) to 107<structfield>maximum</structfield>, inclusive.</para> 108 109 <para>See also the examples in <xref linkend="control" />.</para> 110 111 <table pgwide="1" frame="none" id="v4l2-queryctrl"> 112 <title>struct <structname>v4l2_queryctrl</structname></title> 113 <tgroup cols="3"> 114 &cs-str; 115 <tbody valign="top"> 116 <row> 117 <entry>__u32</entry> 118 <entry><structfield>id</structfield></entry> 119 <entry>Identifies the control, set by the application. See 120<xref linkend="control-id" /> for predefined IDs. When the ID is ORed 121with V4L2_CTRL_FLAG_NEXT_CTRL the driver clears the flag and returns 122the first control with a higher ID. Drivers which do not support this 123flag yet always return an &EINVAL;.</entry> 124 </row> 125 <row> 126 <entry>&v4l2-ctrl-type;</entry> 127 <entry><structfield>type</structfield></entry> 128 <entry>Type of control, see <xref 129 linkend="v4l2-ctrl-type" />.</entry> 130 </row> 131 <row> 132 <entry>__u8</entry> 133 <entry><structfield>name</structfield>[32]</entry> 134 <entry>Name of the control, a NUL-terminated ASCII 135string. This information is intended for the user.</entry> 136 </row> 137 <row> 138 <entry>__s32</entry> 139 <entry><structfield>minimum</structfield></entry> 140 <entry>Minimum value, inclusive. This field gives a lower 141bound for <constant>V4L2_CTRL_TYPE_INTEGER</constant> controls and the 142lowest valid index (always 0) for <constant>V4L2_CTRL_TYPE_MENU</constant> controls. 143For <constant>V4L2_CTRL_TYPE_STRING</constant> controls the minimum value 144gives the minimum length of the string. This length <emphasis>does not include the terminating 145zero</emphasis>. It may not be valid for any other type of control, including 146<constant>V4L2_CTRL_TYPE_INTEGER64</constant> controls. Note that this is a 147signed value.</entry> 148 </row> 149 <row> 150 <entry>__s32</entry> 151 <entry><structfield>maximum</structfield></entry> 152 <entry>Maximum value, inclusive. This field gives an upper 153bound for <constant>V4L2_CTRL_TYPE_INTEGER</constant> controls and the 154highest valid index for <constant>V4L2_CTRL_TYPE_MENU</constant> 155controls. 156For <constant>V4L2_CTRL_TYPE_STRING</constant> controls the maximum value 157gives the maximum length of the string. This length <emphasis>does not include the terminating 158zero</emphasis>. It may not be valid for any other type of control, including 159<constant>V4L2_CTRL_TYPE_INTEGER64</constant> controls. Note that this is a 160signed value.</entry> 161 </row> 162 <row> 163 <entry>__s32</entry> 164 <entry><structfield>step</structfield></entry> 165 <entry><para>This field gives a step size for 166<constant>V4L2_CTRL_TYPE_INTEGER</constant> controls. For 167<constant>V4L2_CTRL_TYPE_STRING</constant> controls this field refers to 168the string length that has to be a multiple of this step size. 169It may not be valid for any other type of control, including 170<constant>V4L2_CTRL_TYPE_INTEGER64</constant> 171controls.</para><para>Generally drivers should not scale hardware 172control values. It may be necessary for example when the 173<structfield>name</structfield> or <structfield>id</structfield> imply 174a particular unit and the hardware actually accepts only multiples of 175said unit. If so, drivers must take care values are properly rounded 176when scaling, such that errors will not accumulate on repeated 177read-write cycles.</para><para>This field gives the smallest change of 178an integer control actually affecting hardware. Often the information 179is needed when the user can change controls by keyboard or GUI 180buttons, rather than a slider. When for example a hardware register 181accepts values 0-511 and the driver reports 0-65535, step should be 182128.</para><para>Note that although signed, the step value is supposed to 183be always positive.</para></entry> 184 </row> 185 <row> 186 <entry>__s32</entry> 187 <entry><structfield>default_value</structfield></entry> 188 <entry>The default value of a 189<constant>V4L2_CTRL_TYPE_INTEGER</constant>, 190<constant>_BOOLEAN</constant> or <constant>_MENU</constant> control. 191Not valid for other types of controls. Drivers reset controls only 192when the driver is loaded, not later, in particular not when the 193func-open; is called.</entry> 194 </row> 195 <row> 196 <entry>__u32</entry> 197 <entry><structfield>flags</structfield></entry> 198 <entry>Control flags, see <xref 199 linkend="control-flags" />.</entry> 200 </row> 201 <row> 202 <entry>__u32</entry> 203 <entry><structfield>reserved</structfield>[2]</entry> 204 <entry>Reserved for future extensions. Drivers must set 205the array to zero.</entry> 206 </row> 207 </tbody> 208 </tgroup> 209 </table> 210 211 <table pgwide="1" frame="none" id="v4l2-querymenu"> 212 <title>struct <structname>v4l2_querymenu</structname></title> 213 <tgroup cols="3"> 214 &cs-str; 215 <tbody valign="top"> 216 <row> 217 <entry>__u32</entry> 218 <entry><structfield>id</structfield></entry> 219 <entry>Identifies the control, set by the application 220from the respective &v4l2-queryctrl; 221<structfield>id</structfield>.</entry> 222 </row> 223 <row> 224 <entry>__u32</entry> 225 <entry><structfield>index</structfield></entry> 226 <entry>Index of the menu item, starting at zero, set by 227 the application.</entry> 228 </row> 229 <row> 230 <entry>__u8</entry> 231 <entry><structfield>name</structfield>[32]</entry> 232 <entry>Name of the menu item, a NUL-terminated ASCII 233string. This information is intended for the user.</entry> 234 </row> 235 <row> 236 <entry>__u32</entry> 237 <entry><structfield>reserved</structfield></entry> 238 <entry>Reserved for future extensions. Drivers must set 239the array to zero.</entry> 240 </row> 241 </tbody> 242 </tgroup> 243 </table> 244 245 <table pgwide="1" frame="none" id="v4l2-ctrl-type"> 246 <title>enum v4l2_ctrl_type</title> 247 <tgroup cols="5" align="left"> 248 <colspec colwidth="30*" /> 249 <colspec colwidth="5*" align="center" /> 250 <colspec colwidth="5*" align="center" /> 251 <colspec colwidth="5*" align="center" /> 252 <colspec colwidth="55*" /> 253 <thead> 254 <row> 255 <entry>Type</entry> 256 <entry><structfield>minimum</structfield></entry> 257 <entry><structfield>step</structfield></entry> 258 <entry><structfield>maximum</structfield></entry> 259 <entry>Description</entry> 260 </row> 261 </thead> 262 <tbody valign="top"> 263 <row> 264 <entry><constant>V4L2_CTRL_TYPE_INTEGER</constant></entry> 265 <entry>any</entry> 266 <entry>any</entry> 267 <entry>any</entry> 268 <entry>An integer-valued control ranging from minimum to 269maximum inclusive. The step value indicates the increment between 270values which are actually different on the hardware.</entry> 271 </row> 272 <row> 273 <entry><constant>V4L2_CTRL_TYPE_BOOLEAN</constant></entry> 274 <entry>0</entry> 275 <entry>1</entry> 276 <entry>1</entry> 277 <entry>A boolean-valued control. Zero corresponds to 278"disabled", and one means "enabled".</entry> 279 </row> 280 <row> 281 <entry><constant>V4L2_CTRL_TYPE_MENU</constant></entry> 282 <entry>0</entry> 283 <entry>1</entry> 284 <entry>N-1</entry> 285 <entry>The control has a menu of N choices. The names of 286the menu items can be enumerated with the 287<constant>VIDIOC_QUERYMENU</constant> ioctl.</entry> 288 </row> 289 <row> 290 <entry><constant>V4L2_CTRL_TYPE_BUTTON</constant></entry> 291 <entry>0</entry> 292 <entry>0</entry> 293 <entry>0</entry> 294 <entry>A control which performs an action when set. 295Drivers must ignore the value passed with 296<constant>VIDIOC_S_CTRL</constant> and return an &EINVAL; on a 297<constant>VIDIOC_G_CTRL</constant> attempt.</entry> 298 </row> 299 <row> 300 <entry><constant>V4L2_CTRL_TYPE_INTEGER64</constant></entry> 301 <entry>n/a</entry> 302 <entry>n/a</entry> 303 <entry>n/a</entry> 304 <entry>A 64-bit integer valued control. Minimum, maximum 305and step size cannot be queried.</entry> 306 </row> 307 <row> 308 <entry><constant>V4L2_CTRL_TYPE_STRING</constant></entry> 309 <entry>≥ 0</entry> 310 <entry>≥ 1</entry> 311 <entry>≥ 0</entry> 312 <entry>The minimum and maximum string lengths. The step size 313means that the string must be (minimum + N * step) characters long for 314N ≥ 0. These lengths do not include the terminating zero, so in order to 315pass a string of length 8 to &VIDIOC-S-EXT-CTRLS; you need to set the 316<structfield>size</structfield> field of &v4l2-ext-control; to 9. For &VIDIOC-G-EXT-CTRLS; you can 317set the <structfield>size</structfield> field to <structfield>maximum</structfield> + 1. 318Which character encoding is used will depend on the string control itself and 319should be part of the control documentation.</entry> 320 </row> 321 <row> 322 <entry><constant>V4L2_CTRL_TYPE_CTRL_CLASS</constant></entry> 323 <entry>n/a</entry> 324 <entry>n/a</entry> 325 <entry>n/a</entry> 326 <entry>This is not a control. When 327<constant>VIDIOC_QUERYCTRL</constant> is called with a control ID 328equal to a control class code (see <xref linkend="ctrl-class" />) + 1, the 329ioctl returns the name of the control class and this control type. 330Older drivers which do not support this feature return an 331&EINVAL;.</entry> 332 </row> 333 </tbody> 334 </tgroup> 335 </table> 336 337 <table pgwide="1" frame="none" id="control-flags"> 338 <title>Control Flags</title> 339 <tgroup cols="3"> 340 &cs-def; 341 <tbody valign="top"> 342 <row> 343 <entry><constant>V4L2_CTRL_FLAG_DISABLED</constant></entry> 344 <entry>0x0001</entry> 345 <entry>This control is permanently disabled and should be 346ignored by the application. Any attempt to change the control will 347result in an &EINVAL;.</entry> 348 </row> 349 <row> 350 <entry><constant>V4L2_CTRL_FLAG_GRABBED</constant></entry> 351 <entry>0x0002</entry> 352 <entry>This control is temporarily unchangeable, for 353example because another application took over control of the 354respective resource. Such controls may be displayed specially in a 355user interface. Attempts to change the control may result in an 356&EBUSY;.</entry> 357 </row> 358 <row> 359 <entry><constant>V4L2_CTRL_FLAG_READ_ONLY</constant></entry> 360 <entry>0x0004</entry> 361 <entry>This control is permanently readable only. Any 362attempt to change the control will result in an &EINVAL;.</entry> 363 </row> 364 <row> 365 <entry><constant>V4L2_CTRL_FLAG_UPDATE</constant></entry> 366 <entry>0x0008</entry> 367 <entry>A hint that changing this control may affect the 368value of other controls within the same control class. Applications 369should update their user interface accordingly.</entry> 370 </row> 371 <row> 372 <entry><constant>V4L2_CTRL_FLAG_INACTIVE</constant></entry> 373 <entry>0x0010</entry> 374 <entry>This control is not applicable to the current 375configuration and should be displayed accordingly in a user interface. 376For example the flag may be set on a MPEG audio level 2 bitrate 377control when MPEG audio encoding level 1 was selected with another 378control.</entry> 379 </row> 380 <row> 381 <entry><constant>V4L2_CTRL_FLAG_SLIDER</constant></entry> 382 <entry>0x0020</entry> 383 <entry>A hint that this control is best represented as a 384slider-like element in a user interface.</entry> 385 </row> 386 <row> 387 <entry><constant>V4L2_CTRL_FLAG_WRITE_ONLY</constant></entry> 388 <entry>0x0040</entry> 389 <entry>This control is permanently writable only. Any 390attempt to read the control will result in an &EACCES; error code. This 391flag is typically present for relative controls or action controls where 392writing a value will cause the device to carry out a given action 393(⪚ motor control) but no meaningful value can be returned.</entry> 394 </row> 395 </tbody> 396 </tgroup> 397 </table> 398 </refsect1> 399 400 <refsect1> 401 &return-value; 402 403 <variablelist> 404 <varlistentry> 405 <term><errorcode>EINVAL</errorcode></term> 406 <listitem> 407 <para>The &v4l2-queryctrl; <structfield>id</structfield> 408is invalid. The &v4l2-querymenu; <structfield>id</structfield> or 409<structfield>index</structfield> is invalid.</para> 410 </listitem> 411 </varlistentry> 412 <varlistentry> 413 <term><errorcode>EACCES</errorcode></term> 414 <listitem> 415 <para>An attempt was made to read a write-only control.</para> 416 </listitem> 417 </varlistentry> 418 </variablelist> 419 </refsect1> 420</refentry> 421 422<!-- 423Local Variables: 424mode: sgml 425sgml-parent-document: "v4l2.sgml" 426indent-tabs-mode: nil 427End: 428--> 429