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``.
188 * - struct :c:type:`v4l2_area` *
190 - A pointer to a struct :c:type:`v4l2_area`. Valid if this control is
191 of type ``V4L2_CTRL_TYPE_AREA``.
192 * - struct :c:type:`v4l2_ctrl_h264_sps` *
194 - A pointer to a struct :c:type:`v4l2_ctrl_h264_sps`. Valid if this control is
195 of type ``V4L2_CTRL_TYPE_H264_SPS``.
196 * - struct :c:type:`v4l2_ctrl_h264_pps` *
198 - A pointer to a struct :c:type:`v4l2_ctrl_h264_pps`. Valid if this control is
199 of type ``V4L2_CTRL_TYPE_H264_PPS``.
200 * - struct :c:type:`v4l2_ctrl_h264_scaling_matrix` *
201 - ``p_h264_scaling_matrix``
202 - A pointer to a struct :c:type:`v4l2_ctrl_h264_scaling_matrix`. Valid if this control is
203 of type ``V4L2_CTRL_TYPE_H264_SCALING_MATRIX``.
204 * - struct :c:type:`v4l2_ctrl_h264_pred_weights` *
205 - ``p_h264_pred_weights``
206 - A pointer to a struct :c:type:`v4l2_ctrl_h264_pred_weights`. Valid if this control is
207 of type ``V4L2_CTRL_TYPE_H264_PRED_WEIGHTS``.
208 * - struct :c:type:`v4l2_ctrl_h264_slice_params` *
209 - ``p_h264_slice_params``
210 - A pointer to a struct :c:type:`v4l2_ctrl_h264_slice_params`. Valid if this control is
211 of type ``V4L2_CTRL_TYPE_H264_SLICE_PARAMS``.
212 * - struct :c:type:`v4l2_ctrl_h264_decode_params` *
213 - ``p_h264_decode_params``
214 - A pointer to a struct :c:type:`v4l2_ctrl_h264_decode_params`. Valid if this control is
215 of type ``V4L2_CTRL_TYPE_H264_DECODE_PARAMS``.
216 * - struct :c:type:`v4l2_ctrl_fwht_params` *
218 - A pointer to a struct :c:type:`v4l2_ctrl_fwht_params`. Valid if this control is
219 of type ``V4L2_CTRL_TYPE_FWHT_PARAMS``.
220 * - struct :c:type:`v4l2_ctrl_vp8_frame` *
222 - A pointer to a struct :c:type:`v4l2_ctrl_vp8_frame`. Valid if this control is
223 of type ``V4L2_CTRL_TYPE_VP8_FRAME``.
224 * - struct :c:type:`v4l2_ctrl_mpeg2_sequence` *
225 - ``p_mpeg2_sequence``
226 - A pointer to a struct :c:type:`v4l2_ctrl_mpeg2_sequence`. Valid if this control is
227 of type ``V4L2_CTRL_TYPE_MPEG2_SEQUENCE``.
228 * - struct :c:type:`v4l2_ctrl_mpeg2_picture` *
229 - ``p_mpeg2_picture``
230 - A pointer to a struct :c:type:`v4l2_ctrl_mpeg2_picture`. Valid if this control is
231 of type ``V4L2_CTRL_TYPE_MPEG2_PICTURE``.
232 * - struct :c:type:`v4l2_ctrl_mpeg2_quantisation` *
233 - ``p_mpeg2_quantisation``
234 - A pointer to a struct :c:type:`v4l2_ctrl_mpeg2_quantisation`. Valid if this control is
235 of type ``V4L2_CTRL_TYPE_MPEG2_QUANTISATION``.
236 * - struct :c:type:`v4l2_ctrl_vp9_compressed_hdr` *
237 - ``p_vp9_compressed_hdr_probs``
238 - A pointer to a struct :c:type:`v4l2_ctrl_vp9_compressed_hdr`. Valid if this
239 control is of type ``V4L2_CTRL_TYPE_VP9_COMPRESSED_HDR``.
240 * - struct :c:type:`v4l2_ctrl_vp9_frame` *
242 - A pointer to a struct :c:type:`v4l2_ctrl_vp9_frame`. Valid if this
243 control is of type ``V4L2_CTRL_TYPE_VP9_FRAME``.
244 * - struct :c:type:`v4l2_ctrl_hdr10_cll_info` *
246 - A pointer to a struct :c:type:`v4l2_ctrl_hdr10_cll_info`. Valid if this control is
247 of type ``V4L2_CTRL_TYPE_HDR10_CLL_INFO``.
248 * - struct :c:type:`v4l2_ctrl_hdr10_mastering_display` *
249 - ``p_hdr10_mastering``
250 - A pointer to a struct :c:type:`v4l2_ctrl_hdr10_mastering_display`. Valid if this control is
251 of type ``V4L2_CTRL_TYPE_HDR10_MASTERING_DISPLAY``.
254 - A pointer to a compound type which can be an N-dimensional array
255 and/or a compound type (the control's type is >=
256 ``V4L2_CTRL_COMPOUND_TYPES``). Valid if
257 ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set for this control.
265 .. tabularcolumns:: |p{4.0cm}|p{2.5cm}|p{10.8cm}|
267 .. c:type:: v4l2_ext_controls
269 .. cssclass:: longtable
271 .. flat-table:: struct v4l2_ext_controls
280 - Which value of the control to get/set/try.
281 * - :cspan:`2` ``V4L2_CTRL_WHICH_CUR_VAL`` will return the current value of
282 the control, ``V4L2_CTRL_WHICH_DEF_VAL`` will return the default
283 value of the control and ``V4L2_CTRL_WHICH_REQUEST_VAL`` indicates that
284 these controls have to be retrieved from a request or tried/set for
285 a request. In the latter case the ``request_fd`` field contains the
286 file descriptor of the request that should be used. If the device
287 does not support requests, then ``EACCES`` will be returned.
289 When using ``V4L2_CTRL_WHICH_DEF_VAL`` be aware that you can only
290 get the default value of the control, you cannot set or try it.
292 For backwards compatibility you can also use a control class here
293 (see :ref:`ctrl-class`). In that case all controls have to
294 belong to that control class. This usage is deprecated, instead
295 just use ``V4L2_CTRL_WHICH_CUR_VAL``. There are some very old
296 drivers that do not yet support ``V4L2_CTRL_WHICH_CUR_VAL`` and
297 that require a control class here. You can test for such drivers
298 by setting ``which`` to ``V4L2_CTRL_WHICH_CUR_VAL`` and calling
299 :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` with a count of 0.
300 If that fails, then the driver does not support ``V4L2_CTRL_WHICH_CUR_VAL``.
303 - Deprecated name kept for backwards compatibility. Use ``which`` instead.
308 - The number of controls in the controls array. May also be zero.
311 - Index of the failing control. Set by the driver in case of an error.
312 * - :cspan:`2` If the error is associated
313 with a particular control, then ``error_idx`` is set to the index
314 of that control. If the error is not related to a specific
315 control, or the validation step failed (see below), then
316 ``error_idx`` is set to ``count``. The value is undefined if the
317 ioctl returned 0 (success).
319 Before controls are read from/written to hardware a validation
320 step takes place: this checks if all controls in the list are
321 valid controls, if no attempt is made to write to a read-only
322 control or read from a write-only control, and any other up-front
323 checks that can be done without accessing the hardware. The exact
324 validations done during this step are driver dependent since some
325 checks might require hardware access for some devices, thus making
326 it impossible to do those checks up-front. However, drivers should
327 make a best-effort to do as many up-front checks as possible.
329 This check is done to avoid leaving the hardware in an
330 inconsistent state due to easy-to-avoid problems. But it leads to
331 another problem: the application needs to know whether an error
332 came from the validation step (meaning that the hardware was not
333 touched) or from an error during the actual reading from/writing
336 The, in hindsight quite poor, solution for that is to set
337 ``error_idx`` to ``count`` if the validation failed. This has the
338 unfortunate side-effect that it is not possible to see which
339 control failed the validation. If the validation was successful
340 and the error happened while accessing the hardware, then
341 ``error_idx`` is less than ``count`` and only the controls up to
342 ``error_idx-1`` were read or written correctly, and the state of
343 the remaining controls is undefined.
345 Since :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` does not access hardware there is
346 also no need to handle the validation step in this special way, so
347 ``error_idx`` will just be set to the control that failed the
348 validation step instead of to ``count``. This means that if
349 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` fails with ``error_idx`` set to ``count``,
350 then you can call :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` to try to discover the
351 actual control that failed the validation step. Unfortunately,
352 there is no ``TRY`` equivalent for :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`.
355 - File descriptor of the request to be used by this operation. Only
356 valid if ``which`` is set to ``V4L2_CTRL_WHICH_REQUEST_VAL``.
357 If the device does not support requests, then ``EACCES`` will be returned.
358 If requests are supported but an invalid request file descriptor is
359 given, then ``EINVAL`` will be returned.
362 - Reserved for future extensions.
364 Drivers and applications must set the array to zero.
365 * - struct :c:type:`v4l2_ext_control` *
367 - Pointer to an array of ``count`` v4l2_ext_control structures.
369 Ignored if ``count`` equals zero.
371 .. tabularcolumns:: |p{7.3cm}|p{2.0cm}|p{8.0cm}|
373 .. cssclass:: longtable
377 .. flat-table:: Control classes
382 * - ``V4L2_CTRL_CLASS_USER``
384 - The class containing user controls. These controls are described
385 in :ref:`control`. All controls that can be set using the
386 :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` and
387 :ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` ioctl belong to this
389 * - ``V4L2_CTRL_CLASS_CODEC``
391 - The class containing stateful codec controls. These controls are
392 described in :ref:`codec-controls`.
393 * - ``V4L2_CTRL_CLASS_CAMERA``
395 - The class containing camera controls. These controls are described
396 in :ref:`camera-controls`.
397 * - ``V4L2_CTRL_CLASS_FM_TX``
399 - The class containing FM Transmitter (FM TX) controls. These
400 controls are described in :ref:`fm-tx-controls`.
401 * - ``V4L2_CTRL_CLASS_FLASH``
403 - The class containing flash device controls. These controls are
404 described in :ref:`flash-controls`.
405 * - ``V4L2_CTRL_CLASS_JPEG``
407 - The class containing JPEG compression controls. These controls are
408 described in :ref:`jpeg-controls`.
409 * - ``V4L2_CTRL_CLASS_IMAGE_SOURCE``
411 - The class containing image source controls. These controls are
412 described in :ref:`image-source-controls`.
413 * - ``V4L2_CTRL_CLASS_IMAGE_PROC``
415 - The class containing image processing controls. These controls are
416 described in :ref:`image-process-controls`.
417 * - ``V4L2_CTRL_CLASS_FM_RX``
419 - The class containing FM Receiver (FM RX) controls. These controls
420 are described in :ref:`fm-rx-controls`.
421 * - ``V4L2_CTRL_CLASS_RF_TUNER``
423 - The class containing RF tuner controls. These controls are
424 described in :ref:`rf-tuner-controls`.
425 * - ``V4L2_CTRL_CLASS_DETECT``
427 - The class containing motion or object detection controls. These controls
428 are described in :ref:`detect-controls`.
429 * - ``V4L2_CTRL_CLASS_CODEC_STATELESS``
431 - The class containing stateless codec controls. These controls are
432 described in :ref:`codec-stateless-controls`.
433 * - ``V4L2_CTRL_CLASS_COLORIMETRY``
435 - The class containing colorimetry controls. These controls are
436 described in :ref:`colorimetry-controls`.
441 On success 0 is returned, on error -1 and the ``errno`` variable is set
442 appropriately. The generic error codes are described at the
443 :ref:`Generic Error Codes <gen-errors>` chapter.
446 The struct :c:type:`v4l2_ext_control` ``id`` is
447 invalid, or the struct :c:type:`v4l2_ext_controls`
448 ``which`` is invalid, or the struct
449 :c:type:`v4l2_ext_control` ``value`` was
450 inappropriate (e.g. the given menu index is not supported by the
451 driver), or the ``which`` field was set to ``V4L2_CTRL_WHICH_REQUEST_VAL``
452 but the given ``request_fd`` was invalid or ``V4L2_CTRL_WHICH_REQUEST_VAL``
453 is not supported by the kernel.
454 This error code is also returned by the
455 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` and :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctls if two or
456 more control values are in conflict.
459 The struct :c:type:`v4l2_ext_control` ``value``
463 The control is temporarily not changeable, possibly because another
464 applications took over control of the device function this control
465 belongs to, or (if the ``which`` field was set to
466 ``V4L2_CTRL_WHICH_REQUEST_VAL``) the request was queued but not yet
470 The space reserved for the control's payload is insufficient. The
471 field ``size`` is set to a value that is enough to store the payload
472 and this error code is returned.
475 Attempt to try or set a read-only control, or to get a write-only
476 control, or to get a control from a request that has not yet been
479 Or the ``which`` field was set to ``V4L2_CTRL_WHICH_REQUEST_VAL`` but the
480 device does not support requests.
482 Or if there is an attempt to set an inactive control and the driver is
483 not capable of caching the new value until the control is active again.