1 .. -*- coding: utf-8; mode: rst -*-
3 .. _VIDIOC_G_EXT_CTRLS:
5 ******************************************************************
6 ioctl VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS, VIDIOC_TRY_EXT_CTRLS
7 ******************************************************************
12 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:function:: int ioctl( int fd, int request, struct v4l2_ext_controls *argp )
25 File descriptor returned by :ref:`open() <func-open>`.
28 VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS,
37 These ioctls allow the caller to get or set multiple controls
38 atomically. Control IDs are grouped into control classes (see
39 :ref:`ctrl-class`) and all controls in the control array must belong
40 to the same control class.
42 Applications must always fill in the ``count``, ``which``, ``controls``
43 and ``reserved`` fields of struct
44 :ref:`v4l2_ext_controls <v4l2-ext-controls>`, and initialize the
45 struct :ref:`v4l2_ext_control <v4l2-ext-control>` array pointed to
46 by the ``controls`` fields.
48 To get the current value of a set of controls applications initialize
49 the ``id``, ``size`` and ``reserved2`` fields of each struct
50 :ref:`v4l2_ext_control <v4l2-ext-control>` and call the
51 :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctl. String controls controls must also set the
52 ``string`` field. Controls of compound types
53 (``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set) must set the ``ptr`` field.
55 If the ``size`` is too small to receive the control result (only
56 relevant for pointer-type controls like strings), then the driver will
57 set ``size`` to a valid value and return an ``ENOSPC`` error code. You
58 should re-allocate the memory to this new size and try again. For the
59 string type it is possible that the same issue occurs again if the
60 string has grown in the meantime. It is recommended to call
61 :ref:`VIDIOC_QUERYCTRL` first and use
62 ``maximum``\ +1 as the new ``size`` value. It is guaranteed that that is
65 N-dimensional arrays are set and retrieved row-by-row. You cannot set a
66 partial array, all elements have to be set or retrieved. The total size
67 is calculated as ``elems`` * ``elem_size``. These values can be obtained
68 by calling :ref:`VIDIOC_QUERY_EXT_CTRL <VIDIOC_QUERYCTRL>`.
70 To change the value of a set of controls applications initialize the
71 ``id``, ``size``, ``reserved2`` and ``value/value64/string/ptr`` fields
72 of each struct :ref:`v4l2_ext_control <v4l2-ext-control>` and call
73 the :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctl. The controls will only be set if *all*
74 control values are valid.
76 To check if a set of controls have correct values applications
77 initialize the ``id``, ``size``, ``reserved2`` and
78 ``value/value64/string/ptr`` fields of each struct
79 :ref:`v4l2_ext_control <v4l2-ext-control>` and call the
80 :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctl. It is up to the driver whether wrong
81 values are automatically adjusted to a valid value or if an error is
84 When the ``id`` or ``which`` is invalid drivers return an ``EINVAL`` error
85 code. When the value is out of bounds drivers can choose to take the
86 closest valid value or return an ``ERANGE`` error code, whatever seems more
87 appropriate. In the first case the new value is set in struct
88 :ref:`v4l2_ext_control <v4l2-ext-control>`. If the new control value
89 is inappropriate (e.g. the given menu index is not supported by the menu
90 control), then this will also result in an ``EINVAL`` error code error.
92 The driver will only set/get these controls if all control values are
93 correct. This prevents the situation where only some of the controls
94 were set/get. Only low-level errors (e. g. a failed i2c command) can
95 still cause this situation.
98 .. tabularcolumns:: |p{1.2cm}|p{3.0cm}|p{1.5cm}|p{11.8cm}|
100 .. _v4l2-ext-control:
102 .. cssclass: longtable
104 .. flat-table:: struct v4l2_ext_control
117 - Identifies the control, set by the application.
126 - The total size in bytes of the payload of this control. This is
127 normally 0, but for pointer controls this should be set to the
128 size of the memory containing the payload, or that will receive
129 the payload. If :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` finds that this value is
130 less than is required to store the payload result, then it is set
131 to a value large enough to store the payload result and ``ENOSPC`` is
136 For string controls, this ``size`` field should
137 not be confused with the length of the string. This field refers
138 to the size of the memory that contains the string. The actual
139 *length* of the string may well be much smaller.
148 - 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
175 - New value or current value. Valid if this control is of type
176 ``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is
186 - A pointer to a string. Valid if this control is of type
187 ``V4L2_CTRL_TYPE_STRING``.
196 - A pointer to a matrix control of unsigned 8-bit values. Valid if
197 this control is of type ``V4L2_CTRL_TYPE_U8``.
206 - A pointer to a matrix control of unsigned 16-bit values. Valid if
207 this control is of type ``V4L2_CTRL_TYPE_U16``.
216 - A pointer to a matrix control of unsigned 32-bit values. Valid if
217 this control is of type ``V4L2_CTRL_TYPE_U32``.
226 - A pointer to a compound type which can be an N-dimensional array
227 and/or a compound type (the control's type is >=
228 ``V4L2_CTRL_COMPOUND_TYPES``). Valid if
229 ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set for this control.
232 .. tabularcolumns:: |p{4.0cm}|p{2.0cm}|p{2.0cm}|p{8.5cm}|
234 .. _v4l2-ext-controls:
236 .. cssclass:: longtable
238 .. flat-table:: struct v4l2_ext_controls
257 - The control class to which all controls belong, see
258 :ref:`ctrl-class`. Drivers that use a kernel framework for
259 handling controls will also accept a value of 0 here, meaning that
260 the controls can belong to any control class. Whether drivers
261 support this can be tested by setting ``ctrl_class`` to 0 and
262 calling :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` with a ``count`` of 0. If that
263 succeeds, then the driver supports this feature.
272 - Which value of the control to get/set/try.
273 ``V4L2_CTRL_WHICH_CUR_VAL`` will return the current value of the
274 control and ``V4L2_CTRL_WHICH_DEF_VAL`` will return the default
275 value of the control.
279 You can only get the default value of the control,
280 you cannot set or try it.
282 For backwards compatibility you can also use a control class here
283 (see :ref:`ctrl-class`). In that case all controls have to
284 belong to that control class. This usage is deprecated, instead
285 just use ``V4L2_CTRL_WHICH_CUR_VAL``. There are some very old
286 drivers that do not yet support ``V4L2_CTRL_WHICH_CUR_VAL`` and
287 that require a control class here. You can test for such drivers
288 by setting ctrl_class to ``V4L2_CTRL_WHICH_CUR_VAL`` and calling
289 VIDIOC_TRY_EXT_CTRLS with a count of 0. If that fails, then the
290 driver does not support ``V4L2_CTRL_WHICH_CUR_VAL``.
298 - The number of controls in the controls array. May also be zero.
306 - Set by the driver in case of an error. If the error is associated
307 with a particular control, then ``error_idx`` is set to the index
308 of that control. If the error is not related to a specific
309 control, or the validation step failed (see below), then
310 ``error_idx`` is set to ``count``. The value is undefined if the
311 ioctl returned 0 (success).
313 Before controls are read from/written to hardware a validation
314 step takes place: this checks if all controls in the list are
315 valid controls, if no attempt is made to write to a read-only
316 control or read from a write-only control, and any other up-front
317 checks that can be done without accessing the hardware. The exact
318 validations done during this step are driver dependent since some
319 checks might require hardware access for some devices, thus making
320 it impossible to do those checks up-front. However, drivers should
321 make a best-effort to do as many up-front checks as possible.
323 This check is done to avoid leaving the hardware in an
324 inconsistent state due to easy-to-avoid problems. But it leads to
325 another problem: the application needs to know whether an error
326 came from the validation step (meaning that the hardware was not
327 touched) or from an error during the actual reading from/writing
330 The, in hindsight quite poor, solution for that is to set
331 ``error_idx`` to ``count`` if the validation failed. This has the
332 unfortunate side-effect that it is not possible to see which
333 control failed the validation. If the validation was successful
334 and the error happened while accessing the hardware, then
335 ``error_idx`` is less than ``count`` and only the controls up to
336 ``error_idx-1`` were read or written correctly, and the state of
337 the remaining controls is undefined.
339 Since :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` does not access hardware there is
340 also no need to handle the validation step in this special way, so
341 ``error_idx`` will just be set to the control that failed the
342 validation step instead of to ``count``. This means that if
343 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` fails with ``error_idx`` set to ``count``,
344 then you can call :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` to try to discover the
345 actual control that failed the validation step. Unfortunately,
346 there is no ``TRY`` equivalent for :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`.
354 - Reserved for future extensions.
356 Drivers and applications must set the array to zero.
360 - struct :ref:`v4l2_ext_control <v4l2-ext-control>` *
364 - Pointer to an array of ``count`` v4l2_ext_control structures.
366 Ignored if ``count`` equals zero.
369 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
373 .. flat-table:: Control classes
381 - ``V4L2_CTRL_CLASS_USER``
385 - The class containing user controls. These controls are described
386 in :ref:`control`. All controls that can be set using the
387 :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` and
388 :ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` ioctl belong to this
393 - ``V4L2_CTRL_CLASS_MPEG``
397 - The class containing MPEG compression controls. These controls are
398 described in :ref:`mpeg-controls`.
402 - ``V4L2_CTRL_CLASS_CAMERA``
406 - The class containing camera controls. These controls are described
407 in :ref:`camera-controls`.
411 - ``V4L2_CTRL_CLASS_FM_TX``
415 - The class containing FM Transmitter (FM TX) controls. These
416 controls are described in :ref:`fm-tx-controls`.
420 - ``V4L2_CTRL_CLASS_FLASH``
424 - The class containing flash device controls. These controls are
425 described in :ref:`flash-controls`.
429 - ``V4L2_CTRL_CLASS_JPEG``
433 - The class containing JPEG compression controls. These controls are
434 described in :ref:`jpeg-controls`.
438 - ``V4L2_CTRL_CLASS_IMAGE_SOURCE``
442 - The class containing image source controls. These controls are
443 described in :ref:`image-source-controls`.
447 - ``V4L2_CTRL_CLASS_IMAGE_PROC``
451 - The class containing image processing controls. These controls are
452 described in :ref:`image-process-controls`.
456 - ``V4L2_CTRL_CLASS_FM_RX``
460 - The class containing FM Receiver (FM RX) controls. These controls
461 are described in :ref:`fm-rx-controls`.
465 - ``V4L2_CTRL_CLASS_RF_TUNER``
469 - The class containing RF tuner controls. These controls are
470 described in :ref:`rf-tuner-controls`.
476 On success 0 is returned, on error -1 and the ``errno`` variable is set
477 appropriately. The generic error codes are described at the
478 :ref:`Generic Error Codes <gen-errors>` chapter.
481 The struct :ref:`v4l2_ext_control <v4l2-ext-control>` ``id`` is
482 invalid, the struct :ref:`v4l2_ext_controls <v4l2-ext-controls>`
483 ``which`` is invalid, or the struct
484 :ref:`v4l2_ext_control <v4l2-ext-control>` ``value`` was
485 inappropriate (e.g. the given menu index is not supported by the
486 driver). This error code is also returned by the
487 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` and :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctls if two or
488 more control values are in conflict.
491 The struct :ref:`v4l2_ext_control <v4l2-ext-control>` ``value``
495 The control is temporarily not changeable, possibly because another
496 applications took over control of the device function this control
500 The space reserved for the control's payload is insufficient. The
501 field ``size`` is set to a value that is enough to store the payload
502 and this error code is returned.
505 Attempt to try or set a read-only control or to get a write-only