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 .. cpp: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.
100 .. tabularcolumns:: |p{3.5cm}|p{3.5cm}|p{3.5cm}|p{7.0cm}|
102 .. flat-table:: struct v4l2_ext_control
115 - Identifies the control, set by the application.
124 - The total size in bytes of the payload of this control. This is
125 normally 0, but for pointer controls this should be set to the
126 size of the memory containing the payload, or that will receive
127 the payload. If :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` finds that this value is
128 less than is required to store the payload result, then it is set
129 to a value large enough to store the payload result and ``ENOSPC`` is
134 For string controls, this ``size`` field should
135 not be confused with the length of the string. This field refers
136 to the size of the memory that contains the string. The actual
137 *length* of the string may well be much smaller.
146 - Reserved for future extensions. Drivers and applications must set
162 - New value or current value. Valid if this control is not of type
163 ``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is
173 - New value or current value. Valid if this control is of type
174 ``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is
184 - A pointer to a string. Valid if this control is of type
185 ``V4L2_CTRL_TYPE_STRING``.
194 - A pointer to a matrix control of unsigned 8-bit values. Valid if
195 this control is of type ``V4L2_CTRL_TYPE_U8``.
204 - A pointer to a matrix control of unsigned 16-bit values. Valid if
205 this control is of type ``V4L2_CTRL_TYPE_U16``.
214 - A pointer to a matrix control of unsigned 32-bit values. Valid if
215 this control is of type ``V4L2_CTRL_TYPE_U32``.
224 - A pointer to a compound type which can be an N-dimensional array
225 and/or a compound type (the control's type is >=
226 ``V4L2_CTRL_COMPOUND_TYPES``). Valid if
227 ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set for this control.
231 .. _v4l2-ext-controls:
233 .. tabularcolumns:: |p{3.5cm}|p{3.5cm}|p{7.0cm}|p{3.5cm}|
235 .. flat-table:: struct v4l2_ext_controls
254 - The control class to which all controls belong, see
255 :ref:`ctrl-class`. Drivers that use a kernel framework for
256 handling controls will also accept a value of 0 here, meaning that
257 the controls can belong to any control class. Whether drivers
258 support this can be tested by setting ``ctrl_class`` to 0 and
259 calling :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` with a ``count`` of 0. If that
260 succeeds, then the driver supports this feature.
269 - Which value of the control to get/set/try.
270 ``V4L2_CTRL_WHICH_CUR_VAL`` will return the current value of the
271 control and ``V4L2_CTRL_WHICH_DEF_VAL`` will return the default
272 value of the control.
276 You can only get the default value of the control,
277 you cannot set or try it.
279 For backwards compatibility you can also use a control class here
280 (see :ref:`ctrl-class`). In that case all controls have to
281 belong to that control class. This usage is deprecated, instead
282 just use ``V4L2_CTRL_WHICH_CUR_VAL``. There are some very old
283 drivers that do not yet support ``V4L2_CTRL_WHICH_CUR_VAL`` and
284 that require a control class here. You can test for such drivers
285 by setting ctrl_class to ``V4L2_CTRL_WHICH_CUR_VAL`` and calling
286 VIDIOC_TRY_EXT_CTRLS with a count of 0. If that fails, then the
287 driver does not support ``V4L2_CTRL_WHICH_CUR_VAL``.
295 - The number of controls in the controls array. May also be zero.
303 - Set by the driver in case of an error. If the error is associated
304 with a particular control, then ``error_idx`` is set to the index
305 of that control. If the error is not related to a specific
306 control, or the validation step failed (see below), then
307 ``error_idx`` is set to ``count``. The value is undefined if the
308 ioctl returned 0 (success).
310 Before controls are read from/written to hardware a validation
311 step takes place: this checks if all controls in the list are
312 valid controls, if no attempt is made to write to a read-only
313 control or read from a write-only control, and any other up-front
314 checks that can be done without accessing the hardware. The exact
315 validations done during this step are driver dependent since some
316 checks might require hardware access for some devices, thus making
317 it impossible to do those checks up-front. However, drivers should
318 make a best-effort to do as many up-front checks as possible.
320 This check is done to avoid leaving the hardware in an
321 inconsistent state due to easy-to-avoid problems. But it leads to
322 another problem: the application needs to know whether an error
323 came from the validation step (meaning that the hardware was not
324 touched) or from an error during the actual reading from/writing
327 The, in hindsight quite poor, solution for that is to set
328 ``error_idx`` to ``count`` if the validation failed. This has the
329 unfortunate side-effect that it is not possible to see which
330 control failed the validation. If the validation was successful
331 and the error happened while accessing the hardware, then
332 ``error_idx`` is less than ``count`` and only the controls up to
333 ``error_idx-1`` were read or written correctly, and the state of
334 the remaining controls is undefined.
336 Since :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` does not access hardware there is
337 also no need to handle the validation step in this special way, so
338 ``error_idx`` will just be set to the control that failed the
339 validation step instead of to ``count``. This means that if
340 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` fails with ``error_idx`` set to ``count``,
341 then you can call :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` to try to discover the
342 actual control that failed the validation step. Unfortunately,
343 there is no ``TRY`` equivalent for :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`.
351 - Reserved for future extensions. Drivers and applications must set
356 - struct :ref:`v4l2_ext_control <v4l2-ext-control>` *
360 - Pointer to an array of ``count`` v4l2_ext_control structures.
361 Ignored if ``count`` equals zero.
367 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
369 .. flat-table:: Control classes
377 - ``V4L2_CTRL_CLASS_USER``
381 - The class containing user controls. These controls are described
382 in :ref:`control`. All controls that can be set using the
383 :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` and
384 :ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` ioctl belong to this
389 - ``V4L2_CTRL_CLASS_MPEG``
393 - The class containing MPEG compression controls. These controls are
394 described in :ref:`mpeg-controls`.
398 - ``V4L2_CTRL_CLASS_CAMERA``
402 - The class containing camera controls. These controls are described
403 in :ref:`camera-controls`.
407 - ``V4L2_CTRL_CLASS_FM_TX``
411 - The class containing FM Transmitter (FM TX) controls. These
412 controls are described in :ref:`fm-tx-controls`.
416 - ``V4L2_CTRL_CLASS_FLASH``
420 - The class containing flash device controls. These controls are
421 described in :ref:`flash-controls`.
425 - ``V4L2_CTRL_CLASS_JPEG``
429 - The class containing JPEG compression controls. These controls are
430 described in :ref:`jpeg-controls`.
434 - ``V4L2_CTRL_CLASS_IMAGE_SOURCE``
438 - The class containing image source controls. These controls are
439 described in :ref:`image-source-controls`.
443 - ``V4L2_CTRL_CLASS_IMAGE_PROC``
447 - The class containing image processing controls. These controls are
448 described in :ref:`image-process-controls`.
452 - ``V4L2_CTRL_CLASS_FM_RX``
456 - The class containing FM Receiver (FM RX) controls. These controls
457 are described in :ref:`fm-rx-controls`.
461 - ``V4L2_CTRL_CLASS_RF_TUNER``
465 - The class containing RF tuner controls. These controls are
466 described in :ref:`rf-tuner-controls`.
472 On success 0 is returned, on error -1 and the ``errno`` variable is set
473 appropriately. The generic error codes are described at the
474 :ref:`Generic Error Codes <gen-errors>` chapter.
477 The struct :ref:`v4l2_ext_control <v4l2-ext-control>` ``id`` is
478 invalid, the struct :ref:`v4l2_ext_controls <v4l2-ext-controls>`
479 ``which`` is invalid, or the struct
480 :ref:`v4l2_ext_control <v4l2-ext-control>` ``value`` was
481 inappropriate (e.g. the given menu index is not supported by the
482 driver). This error code is also returned by the
483 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` and :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctls if two or
484 more control values are in conflict.
487 The struct :ref:`v4l2_ext_control <v4l2-ext-control>` ``value``
491 The control is temporarily not changeable, possibly because another
492 applications took over control of the device function this control
496 The space reserved for the control's payload is insufficient. The
497 field ``size`` is set to a value that is enough to store the payload
498 and this error code is returned.
501 Attempt to try or set a read-only control or to get a write-only