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> to 107<structfield>maximum</structfield>, inclusive. Note that it is possible 108for <constant>VIDIOC_QUERYMENU</constant> to return an &EINVAL; for some 109indices between <structfield>minimum</structfield> and <structfield>maximum</structfield>. 110In that case that particular menu item is not supported by this driver. Also note that 111the <structfield>minimum</structfield> value is not necessarily 0.</para> 112 113 <para>See also the examples in <xref linkend="control" />.</para> 114 115 <table pgwide="1" frame="none" id="v4l2-queryctrl"> 116 <title>struct <structname>v4l2_queryctrl</structname></title> 117 <tgroup cols="3"> 118 &cs-str; 119 <tbody valign="top"> 120 <row> 121 <entry>__u32</entry> 122 <entry><structfield>id</structfield></entry> 123 <entry>Identifies the control, set by the application. See 124<xref linkend="control-id" /> for predefined IDs. When the ID is ORed 125with V4L2_CTRL_FLAG_NEXT_CTRL the driver clears the flag and returns 126the first control with a higher ID. Drivers which do not support this 127flag yet always return an &EINVAL;.</entry> 128 </row> 129 <row> 130 <entry>&v4l2-ctrl-type;</entry> 131 <entry><structfield>type</structfield></entry> 132 <entry>Type of control, see <xref 133 linkend="v4l2-ctrl-type" />.</entry> 134 </row> 135 <row> 136 <entry>__u8</entry> 137 <entry><structfield>name</structfield>[32]</entry> 138 <entry>Name of the control, a NUL-terminated ASCII 139string. This information is intended for the user.</entry> 140 </row> 141 <row> 142 <entry>__s32</entry> 143 <entry><structfield>minimum</structfield></entry> 144 <entry>Minimum value, inclusive. This field gives a lower 145bound for <constant>V4L2_CTRL_TYPE_INTEGER</constant> controls and the 146lowest valid index for <constant>V4L2_CTRL_TYPE_MENU</constant> controls. 147For <constant>V4L2_CTRL_TYPE_STRING</constant> controls the minimum value 148gives the minimum length of the string. This length <emphasis>does not include the terminating 149zero</emphasis>. It may not be valid for any other type of control, including 150<constant>V4L2_CTRL_TYPE_INTEGER64</constant> controls. Note that this is a 151signed value.</entry> 152 </row> 153 <row> 154 <entry>__s32</entry> 155 <entry><structfield>maximum</structfield></entry> 156 <entry>Maximum value, inclusive. This field gives an upper 157bound for <constant>V4L2_CTRL_TYPE_INTEGER</constant> controls and the 158highest valid index for <constant>V4L2_CTRL_TYPE_MENU</constant> 159controls. For <constant>V4L2_CTRL_TYPE_BITMASK</constant> controls it is the 160set of usable bits. 161For <constant>V4L2_CTRL_TYPE_STRING</constant> controls the maximum value 162gives the maximum length of the string. This length <emphasis>does not include the terminating 163zero</emphasis>. It may not be valid for any other type of control, including 164<constant>V4L2_CTRL_TYPE_INTEGER64</constant> controls. Note that this is a 165signed value.</entry> 166 </row> 167 <row> 168 <entry>__s32</entry> 169 <entry><structfield>step</structfield></entry> 170 <entry><para>This field gives a step size for 171<constant>V4L2_CTRL_TYPE_INTEGER</constant> controls. For 172<constant>V4L2_CTRL_TYPE_STRING</constant> controls this field refers to 173the string length that has to be a multiple of this step size. 174It may not be valid for any other type of control, including 175<constant>V4L2_CTRL_TYPE_INTEGER64</constant> 176controls.</para><para>Generally drivers should not scale hardware 177control values. It may be necessary for example when the 178<structfield>name</structfield> or <structfield>id</structfield> imply 179a particular unit and the hardware actually accepts only multiples of 180said unit. If so, drivers must take care values are properly rounded 181when scaling, such that errors will not accumulate on repeated 182read-write cycles.</para><para>This field gives the smallest change of 183an integer control actually affecting hardware. Often the information 184is needed when the user can change controls by keyboard or GUI 185buttons, rather than a slider. When for example a hardware register 186accepts values 0-511 and the driver reports 0-65535, step should be 187128.</para><para>Note that although signed, the step value is supposed to 188be always positive.</para></entry> 189 </row> 190 <row> 191 <entry>__s32</entry> 192 <entry><structfield>default_value</structfield></entry> 193 <entry>The default value of a 194<constant>V4L2_CTRL_TYPE_INTEGER</constant>, 195<constant>_BOOLEAN</constant> or <constant>_MENU</constant> control. 196Not valid for other types of controls. Drivers reset controls only 197when the driver is loaded, not later, in particular not when the 198func-open; is called.</entry> 199 </row> 200 <row> 201 <entry>__u32</entry> 202 <entry><structfield>flags</structfield></entry> 203 <entry>Control flags, see <xref 204 linkend="control-flags" />.</entry> 205 </row> 206 <row> 207 <entry>__u32</entry> 208 <entry><structfield>reserved</structfield>[2]</entry> 209 <entry>Reserved for future extensions. Drivers must set 210the array to zero.</entry> 211 </row> 212 </tbody> 213 </tgroup> 214 </table> 215 216 <table pgwide="1" frame="none" id="v4l2-querymenu"> 217 <title>struct <structname>v4l2_querymenu</structname></title> 218 <tgroup cols="3"> 219 &cs-str; 220 <tbody valign="top"> 221 <row> 222 <entry>__u32</entry> 223 <entry><structfield>id</structfield></entry> 224 <entry>Identifies the control, set by the application 225from the respective &v4l2-queryctrl; 226<structfield>id</structfield>.</entry> 227 </row> 228 <row> 229 <entry>__u32</entry> 230 <entry><structfield>index</structfield></entry> 231 <entry>Index of the menu item, starting at zero, set by 232 the application.</entry> 233 </row> 234 <row> 235 <entry>__u8</entry> 236 <entry><structfield>name</structfield>[32]</entry> 237 <entry>Name of the menu item, a NUL-terminated ASCII 238string. This information is intended for the user.</entry> 239 </row> 240 <row> 241 <entry>__u32</entry> 242 <entry><structfield>reserved</structfield></entry> 243 <entry>Reserved for future extensions. Drivers must set 244the array to zero.</entry> 245 </row> 246 </tbody> 247 </tgroup> 248 </table> 249 250 <table pgwide="1" frame="none" id="v4l2-ctrl-type"> 251 <title>enum v4l2_ctrl_type</title> 252 <tgroup cols="5" align="left"> 253 <colspec colwidth="30*" /> 254 <colspec colwidth="5*" align="center" /> 255 <colspec colwidth="5*" align="center" /> 256 <colspec colwidth="5*" align="center" /> 257 <colspec colwidth="55*" /> 258 <thead> 259 <row> 260 <entry>Type</entry> 261 <entry><structfield>minimum</structfield></entry> 262 <entry><structfield>step</structfield></entry> 263 <entry><structfield>maximum</structfield></entry> 264 <entry>Description</entry> 265 </row> 266 </thead> 267 <tbody valign="top"> 268 <row> 269 <entry><constant>V4L2_CTRL_TYPE_INTEGER</constant></entry> 270 <entry>any</entry> 271 <entry>any</entry> 272 <entry>any</entry> 273 <entry>An integer-valued control ranging from minimum to 274maximum inclusive. The step value indicates the increment between 275values which are actually different on the hardware.</entry> 276 </row> 277 <row> 278 <entry><constant>V4L2_CTRL_TYPE_BOOLEAN</constant></entry> 279 <entry>0</entry> 280 <entry>1</entry> 281 <entry>1</entry> 282 <entry>A boolean-valued control. Zero corresponds to 283"disabled", and one means "enabled".</entry> 284 </row> 285 <row> 286 <entry><constant>V4L2_CTRL_TYPE_MENU</constant></entry> 287 <entry>≥ 0</entry> 288 <entry>1</entry> 289 <entry>N-1</entry> 290 <entry>The control has a menu of N choices. The names of 291the menu items can be enumerated with the 292<constant>VIDIOC_QUERYMENU</constant> ioctl.</entry> 293 </row> 294 <row> 295 <entry><constant>V4L2_CTRL_TYPE_BITMASK</constant></entry> 296 <entry>0</entry> 297 <entry>n/a</entry> 298 <entry>any</entry> 299 <entry>A bitmask field. The maximum value is the set of bits that can 300be used, all other bits are to be 0. The maximum value is interpreted as a __u32, 301allowing the use of bit 31 in the bitmask.</entry> 302 </row> 303 <row> 304 <entry><constant>V4L2_CTRL_TYPE_BUTTON</constant></entry> 305 <entry>0</entry> 306 <entry>0</entry> 307 <entry>0</entry> 308 <entry>A control which performs an action when set. 309Drivers must ignore the value passed with 310<constant>VIDIOC_S_CTRL</constant> and return an &EINVAL; on a 311<constant>VIDIOC_G_CTRL</constant> attempt.</entry> 312 </row> 313 <row> 314 <entry><constant>V4L2_CTRL_TYPE_INTEGER64</constant></entry> 315 <entry>n/a</entry> 316 <entry>n/a</entry> 317 <entry>n/a</entry> 318 <entry>A 64-bit integer valued control. Minimum, maximum 319and step size cannot be queried.</entry> 320 </row> 321 <row> 322 <entry><constant>V4L2_CTRL_TYPE_STRING</constant></entry> 323 <entry>≥ 0</entry> 324 <entry>≥ 1</entry> 325 <entry>≥ 0</entry> 326 <entry>The minimum and maximum string lengths. The step size 327means that the string must be (minimum + N * step) characters long for 328N ≥ 0. These lengths do not include the terminating zero, so in order to 329pass a string of length 8 to &VIDIOC-S-EXT-CTRLS; you need to set the 330<structfield>size</structfield> field of &v4l2-ext-control; to 9. For &VIDIOC-G-EXT-CTRLS; you can 331set the <structfield>size</structfield> field to <structfield>maximum</structfield> + 1. 332Which character encoding is used will depend on the string control itself and 333should be part of the control documentation.</entry> 334 </row> 335 <row> 336 <entry><constant>V4L2_CTRL_TYPE_CTRL_CLASS</constant></entry> 337 <entry>n/a</entry> 338 <entry>n/a</entry> 339 <entry>n/a</entry> 340 <entry>This is not a control. When 341<constant>VIDIOC_QUERYCTRL</constant> is called with a control ID 342equal to a control class code (see <xref linkend="ctrl-class" />) + 1, the 343ioctl returns the name of the control class and this control type. 344Older drivers which do not support this feature return an 345&EINVAL;.</entry> 346 </row> 347 </tbody> 348 </tgroup> 349 </table> 350 351 <table pgwide="1" frame="none" id="control-flags"> 352 <title>Control Flags</title> 353 <tgroup cols="3"> 354 &cs-def; 355 <tbody valign="top"> 356 <row> 357 <entry><constant>V4L2_CTRL_FLAG_DISABLED</constant></entry> 358 <entry>0x0001</entry> 359 <entry>This control is permanently disabled and should be 360ignored by the application. Any attempt to change the control will 361result in an &EINVAL;.</entry> 362 </row> 363 <row> 364 <entry><constant>V4L2_CTRL_FLAG_GRABBED</constant></entry> 365 <entry>0x0002</entry> 366 <entry>This control is temporarily unchangeable, for 367example because another application took over control of the 368respective resource. Such controls may be displayed specially in a 369user interface. Attempts to change the control may result in an 370&EBUSY;.</entry> 371 </row> 372 <row> 373 <entry><constant>V4L2_CTRL_FLAG_READ_ONLY</constant></entry> 374 <entry>0x0004</entry> 375 <entry>This control is permanently readable only. Any 376attempt to change the control will result in an &EINVAL;.</entry> 377 </row> 378 <row> 379 <entry><constant>V4L2_CTRL_FLAG_UPDATE</constant></entry> 380 <entry>0x0008</entry> 381 <entry>A hint that changing this control may affect the 382value of other controls within the same control class. Applications 383should update their user interface accordingly.</entry> 384 </row> 385 <row> 386 <entry><constant>V4L2_CTRL_FLAG_INACTIVE</constant></entry> 387 <entry>0x0010</entry> 388 <entry>This control is not applicable to the current 389configuration and should be displayed accordingly in a user interface. 390For example the flag may be set on a MPEG audio level 2 bitrate 391control when MPEG audio encoding level 1 was selected with another 392control.</entry> 393 </row> 394 <row> 395 <entry><constant>V4L2_CTRL_FLAG_SLIDER</constant></entry> 396 <entry>0x0020</entry> 397 <entry>A hint that this control is best represented as a 398slider-like element in a user interface.</entry> 399 </row> 400 <row> 401 <entry><constant>V4L2_CTRL_FLAG_WRITE_ONLY</constant></entry> 402 <entry>0x0040</entry> 403 <entry>This control is permanently writable only. Any 404attempt to read the control will result in an &EACCES; error code. This 405flag is typically present for relative controls or action controls where 406writing a value will cause the device to carry out a given action 407(⪚ motor control) but no meaningful value can be returned.</entry> 408 </row> 409 <row> 410 <entry><constant>V4L2_CTRL_FLAG_VOLATILE</constant></entry> 411 <entry>0x0080</entry> 412 <entry>This control is volatile, which means that the value of the control 413changes continuously. A typical example would be the current gain value if the device 414is in auto-gain mode. In such a case the hardware calculates the gain value based on 415the lighting conditions which can change over time. Note that setting a new value for 416a volatile control will have no effect. The new value will just be ignored.</entry> 417 </row> 418 </tbody> 419 </tgroup> 420 </table> 421 </refsect1> 422 423 <refsect1> 424 &return-value; 425 426 <variablelist> 427 <varlistentry> 428 <term><errorcode>EINVAL</errorcode></term> 429 <listitem> 430 <para>The &v4l2-queryctrl; <structfield>id</structfield> 431is invalid. The &v4l2-querymenu; <structfield>id</structfield> is 432invalid or <structfield>index</structfield> is out of range (less than 433<structfield>minimum</structfield> or greater than <structfield>maximum</structfield>) 434or this particular menu item is not supported by the driver.</para> 435 </listitem> 436 </varlistentry> 437 <varlistentry> 438 <term><errorcode>EACCES</errorcode></term> 439 <listitem> 440 <para>An attempt was made to read a write-only control.</para> 441 </listitem> 442 </varlistentry> 443 </variablelist> 444 </refsect1> 445</refentry> 446