1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2 3.. _VIDIOC_QUERYCTRL: 4 5******************************************************************* 6ioctls VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL and VIDIOC_QUERYMENU 7******************************************************************* 8 9Name 10==== 11 12VIDIOC_QUERYCTRL - VIDIOC_QUERY_EXT_CTRL - VIDIOC_QUERYMENU - Enumerate controls and menu control items 13 14 15Synopsis 16======== 17 18.. c:function:: int ioctl( int fd, int VIDIOC_QUERYCTRL, struct v4l2_queryctrl *argp ) 19 :name: VIDIOC_QUERYCTRL 20 21.. c:function:: int ioctl( int fd, VIDIOC_QUERY_EXT_CTRL, struct v4l2_query_ext_ctrl *argp ) 22 :name: VIDIOC_QUERY_EXT_CTRL 23 24.. c:function:: int ioctl( int fd, VIDIOC_QUERYMENU, struct v4l2_querymenu *argp ) 25 :name: VIDIOC_QUERYMENU 26 27 28Arguments 29========= 30 31``fd`` 32 File descriptor returned by :ref:`open() <func-open>`. 33 34``argp`` 35 Pointer to struct :c:type:`v4l2_queryctrl`, :c:type:`v4l2_query_ext_ctrl` 36 or :c:type:`v4l2_querymenu` (depending on the ioctl). 37 38 39Description 40=========== 41 42To query the attributes of a control applications set the ``id`` field 43of a struct :ref:`v4l2_queryctrl <v4l2-queryctrl>` and call the 44``VIDIOC_QUERYCTRL`` ioctl with a pointer to this structure. The driver 45fills the rest of the structure or returns an ``EINVAL`` error code when the 46``id`` is invalid. 47 48It is possible to enumerate controls by calling ``VIDIOC_QUERYCTRL`` 49with successive ``id`` values starting from ``V4L2_CID_BASE`` up to and 50exclusive ``V4L2_CID_LASTP1``. Drivers may return ``EINVAL`` if a control in 51this range is not supported. Further applications can enumerate private 52controls, which are not defined in this specification, by starting at 53``V4L2_CID_PRIVATE_BASE`` and incrementing ``id`` until the driver 54returns ``EINVAL``. 55 56In both cases, when the driver sets the ``V4L2_CTRL_FLAG_DISABLED`` flag 57in the ``flags`` field this control is permanently disabled and should 58be ignored by the application. [#f1]_ 59 60When the application ORs ``id`` with ``V4L2_CTRL_FLAG_NEXT_CTRL`` the 61driver returns the next supported non-compound control, or ``EINVAL`` if 62there is none. In addition, the ``V4L2_CTRL_FLAG_NEXT_COMPOUND`` flag 63can be specified to enumerate all compound controls (i.e. controls with 64type ≥ ``V4L2_CTRL_COMPOUND_TYPES`` and/or array control, in other words 65controls that contain more than one value). Specify both 66``V4L2_CTRL_FLAG_NEXT_CTRL`` and ``V4L2_CTRL_FLAG_NEXT_COMPOUND`` in 67order to enumerate all controls, compound or not. Drivers which do not 68support these flags yet always return ``EINVAL``. 69 70The ``VIDIOC_QUERY_EXT_CTRL`` ioctl was introduced in order to better 71support controls that can use compound types, and to expose additional 72control information that cannot be returned in struct 73:ref:`v4l2_queryctrl <v4l2-queryctrl>` since that structure is full. 74 75``VIDIOC_QUERY_EXT_CTRL`` is used in the same way as 76``VIDIOC_QUERYCTRL``, except that the ``reserved`` array must be zeroed 77as well. 78 79Additional information is required for menu controls: the names of the 80menu items. To query them applications set the ``id`` and ``index`` 81fields of struct :ref:`v4l2_querymenu <v4l2-querymenu>` and call the 82``VIDIOC_QUERYMENU`` ioctl with a pointer to this structure. The driver 83fills the rest of the structure or returns an ``EINVAL`` error code when the 84``id`` or ``index`` is invalid. Menu items are enumerated by calling 85``VIDIOC_QUERYMENU`` with successive ``index`` values from struct 86:ref:`v4l2_queryctrl <v4l2-queryctrl>` ``minimum`` to ``maximum``, 87inclusive. 88 89.. note:: 90 91 It is possible for ``VIDIOC_QUERYMENU`` to return 92 an ``EINVAL`` error code for some indices between ``minimum`` and 93 ``maximum``. In that case that particular menu item is not supported by 94 this driver. Also note that the ``minimum`` value is not necessarily 0. 95 96See also the examples in :ref:`control`. 97 98 99.. tabularcolumns:: |p{1.2cm}|p{3.6cm}|p{12.7cm}| 100 101.. _v4l2-queryctrl: 102 103.. cssclass:: longtable 104 105.. flat-table:: struct v4l2_queryctrl 106 :header-rows: 0 107 :stub-columns: 0 108 :widths: 1 1 2 109 110 * - __u32 111 - ``id`` 112 - Identifies the control, set by the application. See 113 :ref:`control-id` for predefined IDs. When the ID is ORed with 114 V4L2_CTRL_FLAG_NEXT_CTRL the driver clears the flag and 115 returns the first control with a higher ID. Drivers which do not 116 support this flag yet always return an ``EINVAL`` error code. 117 * - __u32 118 - ``type`` 119 - Type of control, see :c:type:`v4l2_ctrl_type`. 120 * - __u8 121 - ``name``\ [32] 122 - Name of the control, a NUL-terminated ASCII string. This 123 information is intended for the user. 124 * - __s32 125 - ``minimum`` 126 - Minimum value, inclusive. This field gives a lower bound for the 127 control. See enum :c:type:`v4l2_ctrl_type` how 128 the minimum value is to be used for each possible control type. 129 Note that this a signed 32-bit value. 130 * - __s32 131 - ``maximum`` 132 - Maximum value, inclusive. This field gives an upper bound for the 133 control. See enum :c:type:`v4l2_ctrl_type` how 134 the maximum value is to be used for each possible control type. 135 Note that this a signed 32-bit value. 136 * - __s32 137 - ``step`` 138 - This field gives a step size for the control. See enum 139 :c:type:`v4l2_ctrl_type` how the step value is 140 to be used for each possible control type. Note that this an 141 unsigned 32-bit value. 142 143 Generally drivers should not scale hardware control values. It may 144 be necessary for example when the ``name`` or ``id`` imply a 145 particular unit and the hardware actually accepts only multiples 146 of said unit. If so, drivers must take care values are properly 147 rounded when scaling, such that errors will not accumulate on 148 repeated read-write cycles. 149 150 This field gives the smallest change of an integer control 151 actually affecting hardware. Often the information is needed when 152 the user can change controls by keyboard or GUI buttons, rather 153 than a slider. When for example a hardware register accepts values 154 0-511 and the driver reports 0-65535, step should be 128. 155 156 Note that although signed, the step value is supposed to be always 157 positive. 158 * - __s32 159 - ``default_value`` 160 - The default value of a ``V4L2_CTRL_TYPE_INTEGER``, ``_BOOLEAN``, 161 ``_BITMASK``, ``_MENU`` or ``_INTEGER_MENU`` control. Not valid 162 for other types of controls. 163 164 .. note:: 165 166 Drivers reset controls to their default value only when 167 the driver is first loaded, never afterwards. 168 * - __u32 169 - ``flags`` 170 - Control flags, see :ref:`control-flags`. 171 * - __u32 172 - ``reserved``\ [2] 173 - Reserved for future extensions. Drivers must set the array to 174 zero. 175 176 177 178.. tabularcolumns:: |p{1.2cm}|p{5.0cm}|p{11.3cm}| 179 180.. _v4l2-query-ext-ctrl: 181 182.. cssclass:: longtable 183 184.. flat-table:: struct v4l2_query_ext_ctrl 185 :header-rows: 0 186 :stub-columns: 0 187 :widths: 1 1 2 188 189 * - __u32 190 - ``id`` 191 - Identifies the control, set by the application. See 192 :ref:`control-id` for predefined IDs. When the ID is ORed with 193 ``V4L2_CTRL_FLAG_NEXT_CTRL`` the driver clears the flag and 194 returns the first non-compound control with a higher ID. When the 195 ID is ORed with ``V4L2_CTRL_FLAG_NEXT_COMPOUND`` the driver clears 196 the flag and returns the first compound control with a higher ID. 197 Set both to get the first control (compound or not) with a higher 198 ID. 199 * - __u32 200 - ``type`` 201 - Type of control, see :c:type:`v4l2_ctrl_type`. 202 * - char 203 - ``name``\ [32] 204 - Name of the control, a NUL-terminated ASCII string. This 205 information is intended for the user. 206 * - __s64 207 - ``minimum`` 208 - Minimum value, inclusive. This field gives a lower bound for the 209 control. See enum :c:type:`v4l2_ctrl_type` how 210 the minimum value is to be used for each possible control type. 211 Note that this a signed 64-bit value. 212 * - __s64 213 - ``maximum`` 214 - Maximum value, inclusive. This field gives an upper bound for the 215 control. See enum :c:type:`v4l2_ctrl_type` how 216 the maximum value is to be used for each possible control type. 217 Note that this a signed 64-bit value. 218 * - __u64 219 - ``step`` 220 - This field gives a step size for the control. See enum 221 :c:type:`v4l2_ctrl_type` how the step value is 222 to be used for each possible control type. Note that this an 223 unsigned 64-bit value. 224 225 Generally drivers should not scale hardware control values. It may 226 be necessary for example when the ``name`` or ``id`` imply a 227 particular unit and the hardware actually accepts only multiples 228 of said unit. If so, drivers must take care values are properly 229 rounded when scaling, such that errors will not accumulate on 230 repeated read-write cycles. 231 232 This field gives the smallest change of an integer control 233 actually affecting hardware. Often the information is needed when 234 the user can change controls by keyboard or GUI buttons, rather 235 than a slider. When for example a hardware register accepts values 236 0-511 and the driver reports 0-65535, step should be 128. 237 * - __s64 238 - ``default_value`` 239 - The default value of a ``V4L2_CTRL_TYPE_INTEGER``, ``_INTEGER64``, 240 ``_BOOLEAN``, ``_BITMASK``, ``_MENU``, ``_INTEGER_MENU``, ``_U8`` 241 or ``_U16`` control. Not valid for other types of controls. 242 243 .. note:: 244 245 Drivers reset controls to their default value only when 246 the driver is first loaded, never afterwards. 247 * - __u32 248 - ``flags`` 249 - Control flags, see :ref:`control-flags`. 250 * - __u32 251 - ``elem_size`` 252 - The size in bytes of a single element of the array. Given a char 253 pointer ``p`` to a 3-dimensional array you can find the position 254 of cell ``(z, y, x)`` as follows: 255 ``p + ((z * dims[1] + y) * dims[0] + x) * elem_size``. 256 ``elem_size`` is always valid, also when the control isn't an 257 array. For string controls ``elem_size`` is equal to 258 ``maximum + 1``. 259 * - __u32 260 - ``elems`` 261 - The number of elements in the N-dimensional array. If this control 262 is not an array, then ``elems`` is 1. The ``elems`` field can 263 never be 0. 264 * - __u32 265 - ``nr_of_dims`` 266 - The number of dimension in the N-dimensional array. If this 267 control is not an array, then this field is 0. 268 * - __u32 269 - ``dims[V4L2_CTRL_MAX_DIMS]`` 270 - The size of each dimension. The first ``nr_of_dims`` elements of 271 this array must be non-zero, all remaining elements must be zero. 272 * - __u32 273 - ``reserved``\ [32] 274 - Reserved for future extensions. Applications and drivers must set 275 the array to zero. 276 277 278 279.. tabularcolumns:: |p{1.2cm}|p{1.0cm}|p{1.7cm}|p{13.0cm}| 280 281.. _v4l2-querymenu: 282 283.. flat-table:: struct v4l2_querymenu 284 :header-rows: 0 285 :stub-columns: 0 286 :widths: 1 1 2 287 288 * - __u32 289 - ``id`` 290 - Identifies the control, set by the application from the respective 291 struct :ref:`v4l2_queryctrl <v4l2-queryctrl>` ``id``. 292 * - __u32 293 - ``index`` 294 - Index of the menu item, starting at zero, set by the application. 295 * - union { 296 - (anonymous) 297 * - __u8 298 - ``name``\ [32] 299 - Name of the menu item, a NUL-terminated ASCII string. This 300 information is intended for the user. This field is valid for 301 ``V4L2_CTRL_TYPE_MENU`` type controls. 302 * - __s64 303 - ``value`` 304 - Value of the integer menu item. This field is valid for 305 ``V4L2_CTRL_TYPE_INTEGER_MENU`` type controls. 306 * - } 307 - 308 * - __u32 309 - ``reserved`` 310 - Reserved for future extensions. Drivers must set the array to 311 zero. 312 313 314 315.. tabularcolumns:: |p{5.8cm}|p{1.4cm}|p{1.0cm}|p{1.4cm}|p{6.9cm}| 316 317.. c:type:: v4l2_ctrl_type 318 319.. cssclass:: longtable 320 321.. flat-table:: enum v4l2_ctrl_type 322 :header-rows: 1 323 :stub-columns: 0 324 :widths: 30 5 5 5 55 325 326 * - Type 327 - ``minimum`` 328 - ``step`` 329 - ``maximum`` 330 - Description 331 * - ``V4L2_CTRL_TYPE_INTEGER`` 332 - any 333 - any 334 - any 335 - An integer-valued control ranging from minimum to maximum 336 inclusive. The step value indicates the increment between values. 337 * - ``V4L2_CTRL_TYPE_BOOLEAN`` 338 - 0 339 - 1 340 - 1 341 - A boolean-valued control. Zero corresponds to "disabled", and one 342 means "enabled". 343 * - ``V4L2_CTRL_TYPE_MENU`` 344 - ≥ 0 345 - 1 346 - N-1 347 - The control has a menu of N choices. The names of the menu items 348 can be enumerated with the ``VIDIOC_QUERYMENU`` ioctl. 349 * - ``V4L2_CTRL_TYPE_INTEGER_MENU`` 350 - ≥ 0 351 - 1 352 - N-1 353 - The control has a menu of N choices. The values of the menu items 354 can be enumerated with the ``VIDIOC_QUERYMENU`` ioctl. This is 355 similar to ``V4L2_CTRL_TYPE_MENU`` except that instead of strings, 356 the menu items are signed 64-bit integers. 357 * - ``V4L2_CTRL_TYPE_BITMASK`` 358 - 0 359 - n/a 360 - any 361 - A bitmask field. The maximum value is the set of bits that can be 362 used, all other bits are to be 0. The maximum value is interpreted 363 as a __u32, allowing the use of bit 31 in the bitmask. 364 * - ``V4L2_CTRL_TYPE_BUTTON`` 365 - 0 366 - 0 367 - 0 368 - A control which performs an action when set. Drivers must ignore 369 the value passed with ``VIDIOC_S_CTRL`` and return an ``EACCES`` error 370 code on a ``VIDIOC_G_CTRL`` attempt. 371 * - ``V4L2_CTRL_TYPE_INTEGER64`` 372 - any 373 - any 374 - any 375 - A 64-bit integer valued control. Minimum, maximum and step size 376 cannot be queried using ``VIDIOC_QUERYCTRL``. Only 377 ``VIDIOC_QUERY_EXT_CTRL`` can retrieve the 64-bit min/max/step 378 values, they should be interpreted as n/a when using 379 ``VIDIOC_QUERYCTRL``. 380 * - ``V4L2_CTRL_TYPE_STRING`` 381 - ≥ 0 382 - ≥ 1 383 - ≥ 0 384 - The minimum and maximum string lengths. The step size means that 385 the string must be (minimum + N * step) characters long for N ≥ 0. 386 These lengths do not include the terminating zero, so in order to 387 pass a string of length 8 to 388 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` you need to 389 set the ``size`` field of struct 390 :c:type:`v4l2_ext_control` to 9. For 391 :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` you can set 392 the ``size`` field to ``maximum`` + 1. Which character encoding is 393 used will depend on the string control itself and should be part 394 of the control documentation. 395 * - ``V4L2_CTRL_TYPE_CTRL_CLASS`` 396 - n/a 397 - n/a 398 - n/a 399 - This is not a control. When ``VIDIOC_QUERYCTRL`` is called with a 400 control ID equal to a control class code (see :ref:`ctrl-class`) 401 + 1, the ioctl returns the name of the control class and this 402 control type. Older drivers which do not support this feature 403 return an ``EINVAL`` error code. 404 * - ``V4L2_CTRL_TYPE_U8`` 405 - any 406 - any 407 - any 408 - An unsigned 8-bit valued control ranging from minimum to maximum 409 inclusive. The step value indicates the increment between values. 410 * - ``V4L2_CTRL_TYPE_U16`` 411 - any 412 - any 413 - any 414 - An unsigned 16-bit valued control ranging from minimum to maximum 415 inclusive. The step value indicates the increment between values. 416 * - ``V4L2_CTRL_TYPE_U32`` 417 - any 418 - any 419 - any 420 - An unsigned 32-bit valued control ranging from minimum to maximum 421 inclusive. The step value indicates the increment between values. 422 * - ``V4L2_CTRL_TYPE_MPEG2_SLICE_PARAMS`` 423 - n/a 424 - n/a 425 - n/a 426 - A struct :c:type:`v4l2_ctrl_mpeg2_slice_params`, containing MPEG-2 427 slice parameters for stateless video decoders. 428 * - ``V4L2_CTRL_TYPE_MPEG2_QUANTIZATION`` 429 - n/a 430 - n/a 431 - n/a 432 - A struct :c:type:`v4l2_ctrl_mpeg2_quantization`, containing MPEG-2 433 quantization matrices for stateless video decoders. 434 * - ``V4L2_CTRL_TYPE_AREA`` 435 - n/a 436 - n/a 437 - n/a 438 - A struct :c:type:`v4l2_area`, containing the width and the height 439 of a rectangular area. Units depend on the use case. 440 * - ``V4L2_CTRL_TYPE_H264_SPS`` 441 - n/a 442 - n/a 443 - n/a 444 - A struct :c:type:`v4l2_ctrl_h264_sps`, containing H264 445 sequence parameters for stateless video decoders. 446 * - ``V4L2_CTRL_TYPE_H264_PPS`` 447 - n/a 448 - n/a 449 - n/a 450 - A struct :c:type:`v4l2_ctrl_h264_pps`, containing H264 451 picture parameters for stateless video decoders. 452 * - ``V4L2_CTRL_TYPE_H264_SCALING_MATRIX`` 453 - n/a 454 - n/a 455 - n/a 456 - A struct :c:type:`v4l2_ctrl_h264_scaling_matrix`, containing H264 457 scaling matrices for stateless video decoders. 458 * - ``V4L2_CTRL_TYPE_H264_SLICE_PARAMS`` 459 - n/a 460 - n/a 461 - n/a 462 - A struct :c:type:`v4l2_ctrl_h264_slice_params`, containing H264 463 slice parameters for stateless video decoders. 464 * - ``V4L2_CTRL_TYPE_H264_DECODE_PARAMS`` 465 - n/a 466 - n/a 467 - n/a 468 - A struct :c:type:`v4l2_ctrl_h264_decode_params`, containing H264 469 decode parameters for stateless video decoders. 470 * - ``V4L2_CTRL_TYPE_HEVC_SPS`` 471 - n/a 472 - n/a 473 - n/a 474 - A struct :c:type:`v4l2_ctrl_hevc_sps`, containing HEVC Sequence 475 Parameter Set for stateless video decoders. 476 * - ``V4L2_CTRL_TYPE_HEVC_PPS`` 477 - n/a 478 - n/a 479 - n/a 480 - A struct :c:type:`v4l2_ctrl_hevc_pps`, containing HEVC Picture 481 Parameter Set for stateless video decoders. 482 * - ``V4L2_CTRL_TYPE_HEVC_SLICE_PARAMS`` 483 - n/a 484 - n/a 485 - n/a 486 - A struct :c:type:`v4l2_ctrl_hevc_slice_params`, containing HEVC 487 slice parameters for stateless video decoders. 488 489.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}| 490 491.. _control-flags: 492 493.. cssclass:: longtable 494 495.. flat-table:: Control Flags 496 :header-rows: 0 497 :stub-columns: 0 498 :widths: 3 1 4 499 500 * - ``V4L2_CTRL_FLAG_DISABLED`` 501 - 0x0001 502 - This control is permanently disabled and should be ignored by the 503 application. Any attempt to change the control will result in an 504 ``EINVAL`` error code. 505 * - ``V4L2_CTRL_FLAG_GRABBED`` 506 - 0x0002 507 - This control is temporarily unchangeable, for example because 508 another application took over control of the respective resource. 509 Such controls may be displayed specially in a user interface. 510 Attempts to change the control may result in an ``EBUSY`` error code. 511 * - ``V4L2_CTRL_FLAG_READ_ONLY`` 512 - 0x0004 513 - This control is permanently readable only. Any attempt to change 514 the control will result in an ``EINVAL`` error code. 515 * - ``V4L2_CTRL_FLAG_UPDATE`` 516 - 0x0008 517 - A hint that changing this control may affect the value of other 518 controls within the same control class. Applications should update 519 their user interface accordingly. 520 * - ``V4L2_CTRL_FLAG_INACTIVE`` 521 - 0x0010 522 - This control is not applicable to the current configuration and 523 should be displayed accordingly in a user interface. For example 524 the flag may be set on a MPEG audio level 2 bitrate control when 525 MPEG audio encoding level 1 was selected with another control. 526 * - ``V4L2_CTRL_FLAG_SLIDER`` 527 - 0x0020 528 - A hint that this control is best represented as a slider-like 529 element in a user interface. 530 * - ``V4L2_CTRL_FLAG_WRITE_ONLY`` 531 - 0x0040 532 - This control is permanently writable only. Any attempt to read the 533 control will result in an ``EACCES`` error code error code. This flag 534 is typically present for relative controls or action controls 535 where writing a value will cause the device to carry out a given 536 action (e. g. motor control) but no meaningful value can be 537 returned. 538 * - ``V4L2_CTRL_FLAG_VOLATILE`` 539 - 0x0080 540 - This control is volatile, which means that the value of the 541 control changes continuously. A typical example would be the 542 current gain value if the device is in auto-gain mode. In such a 543 case the hardware calculates the gain value based on the lighting 544 conditions which can change over time. 545 546 .. note:: 547 548 Setting a new value for a volatile control will be ignored 549 unless 550 :ref:`V4L2_CTRL_FLAG_EXECUTE_ON_WRITE <FLAG_EXECUTE_ON_WRITE>` 551 is also set. 552 Setting a new value for a volatile control will *never* trigger a 553 :ref:`V4L2_EVENT_CTRL_CH_VALUE <ctrl-changes-flags>` event. 554 * - ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` 555 - 0x0100 556 - This control has a pointer type, so its value has to be accessed 557 using one of the pointer fields of struct 558 :c:type:`v4l2_ext_control`. This flag is set 559 for controls that are an array, string, or have a compound type. 560 In all cases you have to set a pointer to memory containing the 561 payload of the control. 562 * .. _FLAG_EXECUTE_ON_WRITE: 563 564 - ``V4L2_CTRL_FLAG_EXECUTE_ON_WRITE`` 565 - 0x0200 566 - The value provided to the control will be propagated to the driver 567 even if it remains constant. This is required when the control 568 represents an action on the hardware. For example: clearing an 569 error flag or triggering the flash. All the controls of the type 570 ``V4L2_CTRL_TYPE_BUTTON`` have this flag set. 571 * .. _FLAG_MODIFY_LAYOUT: 572 573 - ``V4L2_CTRL_FLAG_MODIFY_LAYOUT`` 574 - 0x0400 575 - Changing this control value may modify the layout of the 576 buffer (for video devices) or the media bus format (for sub-devices). 577 578 A typical example would be the ``V4L2_CID_ROTATE`` control. 579 580 Note that typically controls with this flag will also set the 581 ``V4L2_CTRL_FLAG_GRABBED`` flag when buffers are allocated or 582 streaming is in progress since most drivers do not support changing 583 the format in that case. 584 585 586Return Value 587============ 588 589On success 0 is returned, on error -1 and the ``errno`` variable is set 590appropriately. The generic error codes are described at the 591:ref:`Generic Error Codes <gen-errors>` chapter. 592 593EINVAL 594 The struct :ref:`v4l2_queryctrl <v4l2-queryctrl>` ``id`` is 595 invalid. The struct :ref:`v4l2_querymenu <v4l2-querymenu>` ``id`` 596 is invalid or ``index`` is out of range (less than ``minimum`` or 597 greater than ``maximum``) or this particular menu item is not 598 supported by the driver. 599 600EACCES 601 An attempt was made to read a write-only control. 602 603.. [#f1] 604 ``V4L2_CTRL_FLAG_DISABLED`` was intended for two purposes: Drivers 605 can skip predefined controls not supported by the hardware (although 606 returning ``EINVAL`` would do as well), or disable predefined and private 607 controls after hardware detection without the trouble of reordering 608 control arrays and indices (``EINVAL`` cannot be used to skip private 609 controls because it would prematurely end the enumeration). 610