1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
4 .. _VIDIOC_G_EXT_CTRLS:
6 ******************************************************************
7 ioctl VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS, VIDIOC_TRY_EXT_CTRLS
8 ******************************************************************
13 VIDIOC_G_EXT_CTRLS - VIDIOC_S_EXT_CTRLS - VIDIOC_TRY_EXT_CTRLS - Get or set the value of several controls, try control values
18 .. c:macro:: VIDIOC_G_EXT_CTRLS
20 ``int ioctl(int fd, VIDIOC_G_EXT_CTRLS, struct v4l2_ext_controls *argp)``
22 .. c:macro:: VIDIOC_S_EXT_CTRLS
24 ``int ioctl(int fd, VIDIOC_S_EXT_CTRLS, struct v4l2_ext_controls *argp)``
26 .. c:macro:: VIDIOC_TRY_EXT_CTRLS
28 ``int ioctl(int fd, VIDIOC_TRY_EXT_CTRLS, struct v4l2_ext_controls *argp)``
34 File descriptor returned by :c:func:`open()`.
37 Pointer to struct :c:type:`v4l2_ext_controls`.
42 These ioctls allow the caller to get or set multiple controls
43 atomically. Control IDs are grouped into control classes (see
44 :ref:`ctrl-class`) and all controls in the control array must belong
45 to the same control class.
47 Applications must always fill in the ``count``, ``which``, ``controls``
48 and ``reserved`` fields of struct
49 :c:type:`v4l2_ext_controls`, and initialize the
50 struct :c:type:`v4l2_ext_control` array pointed to
51 by the ``controls`` fields.
53 To get the current value of a set of controls applications initialize
54 the ``id``, ``size`` and ``reserved2`` fields of each struct
55 :c:type:`v4l2_ext_control` and call the
56 :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctl. String controls must also set the
57 ``string`` field. Controls of compound types
58 (``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set) must set the ``ptr`` field.
60 If the ``size`` is too small to receive the control result (only
61 relevant for pointer-type controls like strings), then the driver will
62 set ``size`` to a valid value and return an ``ENOSPC`` error code. You
63 should re-allocate the memory to this new size and try again. For the
64 string type it is possible that the same issue occurs again if the
65 string has grown in the meantime. It is recommended to call
66 :ref:`VIDIOC_QUERYCTRL` first and use
67 ``maximum``\ +1 as the new ``size`` value. It is guaranteed that that is
70 N-dimensional arrays are set and retrieved row-by-row. You cannot set a
71 partial array, all elements have to be set or retrieved. The total size
72 is calculated as ``elems`` * ``elem_size``. These values can be obtained
73 by calling :ref:`VIDIOC_QUERY_EXT_CTRL <VIDIOC_QUERYCTRL>`.
75 To change the value of a set of controls applications initialize the
76 ``id``, ``size``, ``reserved2`` and ``value/value64/string/ptr`` fields
77 of each struct :c:type:`v4l2_ext_control` and call
78 the :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctl. The controls will only be set if *all*
79 control values are valid.
81 To check if a set of controls have correct values applications
82 initialize the ``id``, ``size``, ``reserved2`` and
83 ``value/value64/string/ptr`` fields of each struct
84 :c:type:`v4l2_ext_control` and call the
85 :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctl. It is up to the driver whether wrong
86 values are automatically adjusted to a valid value or if an error is
89 When the ``id`` or ``which`` is invalid drivers return an ``EINVAL`` error
90 code. When the value is out of bounds drivers can choose to take the
91 closest valid value or return an ``ERANGE`` error code, whatever seems more
92 appropriate. In the first case the new value is set in struct
93 :c:type:`v4l2_ext_control`. If the new control value
94 is inappropriate (e.g. the given menu index is not supported by the menu
95 control), then this will also result in an ``EINVAL`` error code error.
97 If ``request_fd`` is set to a not-yet-queued :ref:`request <media-request-api>`
98 file descriptor and ``which`` is set to ``V4L2_CTRL_WHICH_REQUEST_VAL``,
99 then the controls are not applied immediately when calling
100 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`, but instead are applied by
101 the driver for the buffer associated with the same request.
102 If the device does not support requests, then ``EACCES`` will be returned.
103 If requests are supported but an invalid request file descriptor is given,
104 then ``EINVAL`` will be returned.
106 An attempt to call :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` for a
107 request that has already been queued will result in an ``EBUSY`` error.
109 If ``request_fd`` is specified and ``which`` is set to
110 ``V4L2_CTRL_WHICH_REQUEST_VAL`` during a call to
111 :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`, then it will return the
112 values of the controls at the time of request completion.
113 If the request is not yet completed, then this will result in an
116 The driver will only set/get these controls if all control values are
117 correct. This prevents the situation where only some of the controls
118 were set/get. Only low-level errors (e. g. a failed i2c command) can
119 still cause this situation.
121 .. tabularcolumns:: |p{6.8cm}|p{4.0cm}|p{6.5cm}|
123 .. c:type:: v4l2_ext_control
129 .. cssclass:: longtable
131 .. flat-table:: struct v4l2_ext_control
138 - Identifies the control, set by the application.
141 - The total size in bytes of the payload of this control.
142 * - :cspan:`2` The ``size`` field is normally 0, but for pointer
143 controls this should be set to the size of the memory that contains
144 the payload or that will receive the payload.
145 If :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` finds that this value
146 is less than is required to store the payload result, then it is set
147 to a value large enough to store the payload result and ``ENOSPC`` is
152 For string controls, this ``size`` field should
153 not be confused with the length of the string. This field refers
154 to the size of the memory that contains the string. The actual
155 *length* of the string may well be much smaller.
158 - Reserved for future extensions. Drivers and applications must set
164 - New value or current value. Valid if this control is not of type
165 ``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is
169 - New value or current value. Valid if this control is of type
170 ``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is
174 - A pointer to a string. Valid if this control is of type
175 ``V4L2_CTRL_TYPE_STRING``.
178 - A pointer to a matrix control of unsigned 8-bit values. Valid if
179 this control is of type ``V4L2_CTRL_TYPE_U8``.
182 - A pointer to a matrix control of unsigned 16-bit values. Valid if
183 this control is of type ``V4L2_CTRL_TYPE_U16``.
186 - A pointer to a matrix control of unsigned 32-bit values. Valid if
187 this control is of type ``V4L2_CTRL_TYPE_U32``.
190 - A pointer to a matrix control of signed 32-bit values. Valid if
191 this control is of type ``V4L2_CTRL_TYPE_INTEGER`` and
192 ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set.
195 - A pointer to a matrix control of signed 64-bit values. Valid if
196 this control is of type ``V4L2_CTRL_TYPE_INTEGER64`` and
197 ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set.
198 * - struct :c:type:`v4l2_area` *
200 - A pointer to a struct :c:type:`v4l2_area`. Valid if this control is
201 of type ``V4L2_CTRL_TYPE_AREA``.
202 * - struct :c:type:`v4l2_ctrl_h264_sps` *
204 - A pointer to a struct :c:type:`v4l2_ctrl_h264_sps`. Valid if this control is
205 of type ``V4L2_CTRL_TYPE_H264_SPS``.
206 * - struct :c:type:`v4l2_ctrl_h264_pps` *
208 - A pointer to a struct :c:type:`v4l2_ctrl_h264_pps`. Valid if this control is
209 of type ``V4L2_CTRL_TYPE_H264_PPS``.
210 * - struct :c:type:`v4l2_ctrl_h264_scaling_matrix` *
211 - ``p_h264_scaling_matrix``
212 - A pointer to a struct :c:type:`v4l2_ctrl_h264_scaling_matrix`. Valid if this control is
213 of type ``V4L2_CTRL_TYPE_H264_SCALING_MATRIX``.
214 * - struct :c:type:`v4l2_ctrl_h264_pred_weights` *
215 - ``p_h264_pred_weights``
216 - A pointer to a struct :c:type:`v4l2_ctrl_h264_pred_weights`. Valid if this control is
217 of type ``V4L2_CTRL_TYPE_H264_PRED_WEIGHTS``.
218 * - struct :c:type:`v4l2_ctrl_h264_slice_params` *
219 - ``p_h264_slice_params``
220 - A pointer to a struct :c:type:`v4l2_ctrl_h264_slice_params`. Valid if this control is
221 of type ``V4L2_CTRL_TYPE_H264_SLICE_PARAMS``.
222 * - struct :c:type:`v4l2_ctrl_h264_decode_params` *
223 - ``p_h264_decode_params``
224 - A pointer to a struct :c:type:`v4l2_ctrl_h264_decode_params`. Valid if this control is
225 of type ``V4L2_CTRL_TYPE_H264_DECODE_PARAMS``.
226 * - struct :c:type:`v4l2_ctrl_fwht_params` *
228 - A pointer to a struct :c:type:`v4l2_ctrl_fwht_params`. Valid if this control is
229 of type ``V4L2_CTRL_TYPE_FWHT_PARAMS``.
230 * - struct :c:type:`v4l2_ctrl_vp8_frame` *
232 - A pointer to a struct :c:type:`v4l2_ctrl_vp8_frame`. Valid if this control is
233 of type ``V4L2_CTRL_TYPE_VP8_FRAME``.
234 * - struct :c:type:`v4l2_ctrl_mpeg2_sequence` *
235 - ``p_mpeg2_sequence``
236 - A pointer to a struct :c:type:`v4l2_ctrl_mpeg2_sequence`. Valid if this control is
237 of type ``V4L2_CTRL_TYPE_MPEG2_SEQUENCE``.
238 * - struct :c:type:`v4l2_ctrl_mpeg2_picture` *
239 - ``p_mpeg2_picture``
240 - A pointer to a struct :c:type:`v4l2_ctrl_mpeg2_picture`. Valid if this control is
241 of type ``V4L2_CTRL_TYPE_MPEG2_PICTURE``.
242 * - struct :c:type:`v4l2_ctrl_mpeg2_quantisation` *
243 - ``p_mpeg2_quantisation``
244 - A pointer to a struct :c:type:`v4l2_ctrl_mpeg2_quantisation`. Valid if this control is
245 of type ``V4L2_CTRL_TYPE_MPEG2_QUANTISATION``.
246 * - struct :c:type:`v4l2_ctrl_vp9_compressed_hdr` *
247 - ``p_vp9_compressed_hdr_probs``
248 - A pointer to a struct :c:type:`v4l2_ctrl_vp9_compressed_hdr`. Valid if this
249 control is of type ``V4L2_CTRL_TYPE_VP9_COMPRESSED_HDR``.
250 * - struct :c:type:`v4l2_ctrl_vp9_frame` *
252 - A pointer to a struct :c:type:`v4l2_ctrl_vp9_frame`. Valid if this
253 control is of type ``V4L2_CTRL_TYPE_VP9_FRAME``.
254 * - struct :c:type:`v4l2_ctrl_hdr10_cll_info` *
256 - A pointer to a struct :c:type:`v4l2_ctrl_hdr10_cll_info`. Valid if this control is
257 of type ``V4L2_CTRL_TYPE_HDR10_CLL_INFO``.
258 * - struct :c:type:`v4l2_ctrl_hdr10_mastering_display` *
259 - ``p_hdr10_mastering``
260 - A pointer to a struct :c:type:`v4l2_ctrl_hdr10_mastering_display`. Valid if this control is
261 of type ``V4L2_CTRL_TYPE_HDR10_MASTERING_DISPLAY``.
262 * - struct :c:type:`v4l2_ctrl_hevc_sps` *
264 - A pointer to a struct :c:type:`v4l2_ctrl_hevc_sps`. Valid if this
265 control is of type ``V4L2_CTRL_TYPE_HEVC_SPS``.
266 * - struct :c:type:`v4l2_ctrl_hevc_pps` *
268 - A pointer to a struct :c:type:`v4l2_ctrl_hevc_pps`. Valid if this
269 control is of type ``V4L2_CTRL_TYPE_HEVC_PPS``.
270 * - struct :c:type:`v4l2_ctrl_hevc_slice_params` *
271 - ``p_hevc_slice_params``
272 - A pointer to a struct :c:type:`v4l2_ctrl_hevc_slice_params`. Valid if this
273 control is of type ``V4L2_CTRL_TYPE_HEVC_SLICE_PARAMS``.
274 * - struct :c:type:`v4l2_ctrl_hevc_scaling_matrix` *
275 - ``p_hevc_scaling_matrix``
276 - A pointer to a struct :c:type:`v4l2_ctrl_hevc_scaling_matrix`. Valid if this
277 control is of type ``V4L2_CTRL_TYPE_HEVC_SCALING_MATRIX``.
278 * - struct :c:type:`v4l2_ctrl_hevc_decode_params` *
279 - ``p_hevc_decode_params``
280 - A pointer to a struct :c:type:`v4l2_ctrl_hevc_decode_params`. Valid if this
281 control is of type ``V4L2_CTRL_TYPE_HEVC_DECODE_PARAMS``.
282 * - struct :c:type:`v4l2_ctrl_av1_sequence` *
284 - A pointer to a struct :c:type:`v4l2_ctrl_av1_sequence`. Valid if this control is
285 of type ``V4L2_CTRL_TYPE_AV1_SEQUENCE``.
286 * - struct :c:type:`v4l2_ctrl_av1_tile_group_entry` *
287 - ``p_av1_tile_group_entry``
288 - A pointer to a struct :c:type:`v4l2_ctrl_av1_tile_group_entry`. Valid if this control is
289 of type ``V4L2_CTRL_TYPE_AV1_TILE_GROUP_ENTRY``.
290 * - struct :c:type:`v4l2_ctrl_av1_frame` *
292 - A pointer to a struct :c:type:`v4l2_ctrl_av1_frame`. Valid if this control is
293 of type ``V4L2_CTRL_TYPE_AV1_FRAME``.
294 * - struct :c:type:`v4l2_ctrl_av1_film_grain` *
295 - ``p_av1_film_grain``
296 - A pointer to a struct :c:type:`v4l2_ctrl_av1_film_grain`. Valid if this control is
297 of type ``V4L2_CTRL_TYPE_AV1_FILM_GRAIN``.
300 - A pointer to a compound type which can be an N-dimensional array
301 and/or a compound type (the control's type is >=
302 ``V4L2_CTRL_COMPOUND_TYPES``). Valid if
303 ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set for this control.
311 .. tabularcolumns:: |p{4.0cm}|p{2.5cm}|p{10.8cm}|
313 .. c:type:: v4l2_ext_controls
315 .. cssclass:: longtable
317 .. flat-table:: struct v4l2_ext_controls
326 - Which value of the control to get/set/try.
327 * - :cspan:`2` ``V4L2_CTRL_WHICH_CUR_VAL`` will return the current value of
328 the control, ``V4L2_CTRL_WHICH_DEF_VAL`` will return the default
329 value of the control and ``V4L2_CTRL_WHICH_REQUEST_VAL`` indicates that
330 these controls have to be retrieved from a request or tried/set for
331 a request. In the latter case the ``request_fd`` field contains the
332 file descriptor of the request that should be used. If the device
333 does not support requests, then ``EACCES`` will be returned.
335 When using ``V4L2_CTRL_WHICH_DEF_VAL`` be aware that you can only
336 get the default value of the control, you cannot set or try it.
338 For backwards compatibility you can also use a control class here
339 (see :ref:`ctrl-class`). In that case all controls have to
340 belong to that control class. This usage is deprecated, instead
341 just use ``V4L2_CTRL_WHICH_CUR_VAL``. There are some very old
342 drivers that do not yet support ``V4L2_CTRL_WHICH_CUR_VAL`` and
343 that require a control class here. You can test for such drivers
344 by setting ``which`` to ``V4L2_CTRL_WHICH_CUR_VAL`` and calling
345 :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` with a count of 0.
346 If that fails, then the driver does not support ``V4L2_CTRL_WHICH_CUR_VAL``.
349 - Deprecated name kept for backwards compatibility. Use ``which`` instead.
354 - The number of controls in the controls array. May also be zero.
357 - Index of the failing control. Set by the driver in case of an error.
358 * - :cspan:`2` If the error is associated
359 with a particular control, then ``error_idx`` is set to the index
360 of that control. If the error is not related to a specific
361 control, or the validation step failed (see below), then
362 ``error_idx`` is set to ``count``. The value is undefined if the
363 ioctl returned 0 (success).
365 Before controls are read from/written to hardware a validation
366 step takes place: this checks if all controls in the list are
367 valid controls, if no attempt is made to write to a read-only
368 control or read from a write-only control, and any other up-front
369 checks that can be done without accessing the hardware. The exact
370 validations done during this step are driver dependent since some
371 checks might require hardware access for some devices, thus making
372 it impossible to do those checks up-front. However, drivers should
373 make a best-effort to do as many up-front checks as possible.
375 This check is done to avoid leaving the hardware in an
376 inconsistent state due to easy-to-avoid problems. But it leads to
377 another problem: the application needs to know whether an error
378 came from the validation step (meaning that the hardware was not
379 touched) or from an error during the actual reading from/writing
382 The, in hindsight quite poor, solution for that is to set
383 ``error_idx`` to ``count`` if the validation failed. This has the
384 unfortunate side-effect that it is not possible to see which
385 control failed the validation. If the validation was successful
386 and the error happened while accessing the hardware, then
387 ``error_idx`` is less than ``count`` and only the controls up to
388 ``error_idx-1`` were read or written correctly, and the state of
389 the remaining controls is undefined.
391 Since :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` does not access hardware there is
392 also no need to handle the validation step in this special way, so
393 ``error_idx`` will just be set to the control that failed the
394 validation step instead of to ``count``. This means that if
395 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` fails with ``error_idx`` set to ``count``,
396 then you can call :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` to try to discover the
397 actual control that failed the validation step. Unfortunately,
398 there is no ``TRY`` equivalent for :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`.
401 - File descriptor of the request to be used by this operation. Only
402 valid if ``which`` is set to ``V4L2_CTRL_WHICH_REQUEST_VAL``.
403 If the device does not support requests, then ``EACCES`` will be returned.
404 If requests are supported but an invalid request file descriptor is
405 given, then ``EINVAL`` will be returned.
408 - Reserved for future extensions.
410 Drivers and applications must set the array to zero.
411 * - struct :c:type:`v4l2_ext_control` *
413 - Pointer to an array of ``count`` v4l2_ext_control structures.
415 Ignored if ``count`` equals zero.
417 .. tabularcolumns:: |p{7.3cm}|p{2.0cm}|p{8.0cm}|
419 .. cssclass:: longtable
423 .. flat-table:: Control classes
428 * - ``V4L2_CTRL_CLASS_USER``
430 - The class containing user controls. These controls are described
431 in :ref:`control`. All controls that can be set using the
432 :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` and
433 :ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` ioctl belong to this
435 * - ``V4L2_CTRL_CLASS_CODEC``
437 - The class containing stateful codec controls. These controls are
438 described in :ref:`codec-controls`.
439 * - ``V4L2_CTRL_CLASS_CAMERA``
441 - The class containing camera controls. These controls are described
442 in :ref:`camera-controls`.
443 * - ``V4L2_CTRL_CLASS_FM_TX``
445 - The class containing FM Transmitter (FM TX) controls. These
446 controls are described in :ref:`fm-tx-controls`.
447 * - ``V4L2_CTRL_CLASS_FLASH``
449 - The class containing flash device controls. These controls are
450 described in :ref:`flash-controls`.
451 * - ``V4L2_CTRL_CLASS_JPEG``
453 - The class containing JPEG compression controls. These controls are
454 described in :ref:`jpeg-controls`.
455 * - ``V4L2_CTRL_CLASS_IMAGE_SOURCE``
457 - The class containing image source controls. These controls are
458 described in :ref:`image-source-controls`.
459 * - ``V4L2_CTRL_CLASS_IMAGE_PROC``
461 - The class containing image processing controls. These controls are
462 described in :ref:`image-process-controls`.
463 * - ``V4L2_CTRL_CLASS_FM_RX``
465 - The class containing FM Receiver (FM RX) controls. These controls
466 are described in :ref:`fm-rx-controls`.
467 * - ``V4L2_CTRL_CLASS_RF_TUNER``
469 - The class containing RF tuner controls. These controls are
470 described in :ref:`rf-tuner-controls`.
471 * - ``V4L2_CTRL_CLASS_DETECT``
473 - The class containing motion or object detection controls. These controls
474 are described in :ref:`detect-controls`.
475 * - ``V4L2_CTRL_CLASS_CODEC_STATELESS``
477 - The class containing stateless codec controls. These controls are
478 described in :ref:`codec-stateless-controls`.
479 * - ``V4L2_CTRL_CLASS_COLORIMETRY``
481 - The class containing colorimetry controls. These controls are
482 described in :ref:`colorimetry-controls`.
487 On success 0 is returned, on error -1 and the ``errno`` variable is set
488 appropriately. The generic error codes are described at the
489 :ref:`Generic Error Codes <gen-errors>` chapter.
492 The struct :c:type:`v4l2_ext_control` ``id`` is
493 invalid, or the struct :c:type:`v4l2_ext_controls`
494 ``which`` is invalid, or the struct
495 :c:type:`v4l2_ext_control` ``value`` was
496 inappropriate (e.g. the given menu index is not supported by the
497 driver), or the ``which`` field was set to ``V4L2_CTRL_WHICH_REQUEST_VAL``
498 but the given ``request_fd`` was invalid or ``V4L2_CTRL_WHICH_REQUEST_VAL``
499 is not supported by the kernel.
500 This error code is also returned by the
501 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` and :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctls if two or
502 more control values are in conflict.
505 The struct :c:type:`v4l2_ext_control` ``value``
509 The control is temporarily not changeable, possibly because another
510 applications took over control of the device function this control
511 belongs to, or (if the ``which`` field was set to
512 ``V4L2_CTRL_WHICH_REQUEST_VAL``) the request was queued but not yet
516 The space reserved for the control's payload is insufficient. The
517 field ``size`` is set to a value that is enough to store the payload
518 and this error code is returned.
521 Attempt to try or set a read-only control, or to get a write-only
522 control, or to get a control from a request that has not yet been
525 Or the ``which`` field was set to ``V4L2_CTRL_WHICH_REQUEST_VAL`` but the
526 device does not support requests.
528 Or if there is an attempt to set an inactive control and the driver is
529 not capable of caching the new value until the control is active again.