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, VIDIOC_G_EXT_CTRLS, struct v4l2_ext_controls *argp )
19 :name: VIDIOC_G_EXT_CTRLS
22 .. c:function:: int ioctl( int fd, VIDIOC_S_EXT_CTRLS, struct v4l2_ext_controls *argp )
23 :name: VIDIOC_S_EXT_CTRLS
26 .. c:function:: int ioctl( int fd, VIDIOC_TRY_EXT_CTRLS, struct v4l2_ext_controls *argp )
27 :name: VIDIOC_TRY_EXT_CTRLS
34 File descriptor returned by :ref:`open() <func-open>`.
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 :ref:`v4l2_ext_controls <v4l2-ext-controls>`, and initialize the
50 struct :ref:`v4l2_ext_control <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 :ref:`v4l2_ext_control <v4l2-ext-control>` and call the
56 :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctl. String controls 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 :ref:`v4l2_ext_control <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 :ref:`v4l2_ext_control <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 :ref:`v4l2_ext_control <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 The driver will only set/get these controls if all control values are
98 correct. This prevents the situation where only some of the controls
99 were set/get. Only low-level errors (e. g. a failed i2c command) can
100 still cause this situation.
103 .. tabularcolumns:: |p{1.2cm}|p{3.0cm}|p{1.5cm}|p{11.8cm}|
105 .. _v4l2-ext-control:
107 .. cssclass: longtable
109 .. flat-table:: struct v4l2_ext_control
122 - Identifies the control, set by the application.
131 - The total size in bytes of the payload of this control. This is
132 normally 0, but for pointer controls this should be set to the
133 size of the memory containing the payload, or that will receive
134 the payload. If :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` finds that this value is
135 less than is required to store the payload result, then it is set
136 to a value large enough to store the payload result and ``ENOSPC`` is
141 For string controls, this ``size`` field should
142 not be confused with the length of the string. This field refers
143 to the size of the memory that contains the string. The actual
144 *length* of the string may well be much smaller.
153 - Reserved for future extensions. Drivers and applications must set
169 - New value or current value. Valid if this control is not of type
170 ``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is
180 - New value or current value. Valid if this control is of type
181 ``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is
191 - A pointer to a string. Valid if this control is of type
192 ``V4L2_CTRL_TYPE_STRING``.
201 - A pointer to a matrix control of unsigned 8-bit values. Valid if
202 this control is of type ``V4L2_CTRL_TYPE_U8``.
211 - A pointer to a matrix control of unsigned 16-bit values. Valid if
212 this control is of type ``V4L2_CTRL_TYPE_U16``.
221 - A pointer to a matrix control of unsigned 32-bit values. Valid if
222 this control is of type ``V4L2_CTRL_TYPE_U32``.
231 - A pointer to a compound type which can be an N-dimensional array
232 and/or a compound type (the control's type is >=
233 ``V4L2_CTRL_COMPOUND_TYPES``). Valid if
234 ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set for this control.
237 .. tabularcolumns:: |p{4.0cm}|p{2.0cm}|p{2.0cm}|p{8.5cm}|
239 .. _v4l2-ext-controls:
241 .. cssclass:: longtable
243 .. flat-table:: struct v4l2_ext_controls
262 - The control class to which all controls belong, see
263 :ref:`ctrl-class`. Drivers that use a kernel framework for
264 handling controls will also accept a value of 0 here, meaning that
265 the controls can belong to any control class. Whether drivers
266 support this can be tested by setting ``ctrl_class`` to 0 and
267 calling :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` with a ``count`` of 0. If that
268 succeeds, then the driver supports this feature.
277 - Which value of the control to get/set/try.
278 ``V4L2_CTRL_WHICH_CUR_VAL`` will return the current value of the
279 control and ``V4L2_CTRL_WHICH_DEF_VAL`` will return the default
280 value of the control.
284 You can only get the default value of the control,
285 you cannot set or try it.
287 For backwards compatibility you can also use a control class here
288 (see :ref:`ctrl-class`). In that case all controls have to
289 belong to that control class. This usage is deprecated, instead
290 just use ``V4L2_CTRL_WHICH_CUR_VAL``. There are some very old
291 drivers that do not yet support ``V4L2_CTRL_WHICH_CUR_VAL`` and
292 that require a control class here. You can test for such drivers
293 by setting ctrl_class to ``V4L2_CTRL_WHICH_CUR_VAL`` and calling
294 VIDIOC_TRY_EXT_CTRLS with a count of 0. If that fails, then the
295 driver does not support ``V4L2_CTRL_WHICH_CUR_VAL``.
303 - The number of controls in the controls array. May also be zero.
311 - Set by the driver in case of an error. If the error is associated
312 with a particular control, then ``error_idx`` is set to the index
313 of that control. If the error is not related to a specific
314 control, or the validation step failed (see below), then
315 ``error_idx`` is set to ``count``. The value is undefined if the
316 ioctl returned 0 (success).
318 Before controls are read from/written to hardware a validation
319 step takes place: this checks if all controls in the list are
320 valid controls, if no attempt is made to write to a read-only
321 control or read from a write-only control, and any other up-front
322 checks that can be done without accessing the hardware. The exact
323 validations done during this step are driver dependent since some
324 checks might require hardware access for some devices, thus making
325 it impossible to do those checks up-front. However, drivers should
326 make a best-effort to do as many up-front checks as possible.
328 This check is done to avoid leaving the hardware in an
329 inconsistent state due to easy-to-avoid problems. But it leads to
330 another problem: the application needs to know whether an error
331 came from the validation step (meaning that the hardware was not
332 touched) or from an error during the actual reading from/writing
335 The, in hindsight quite poor, solution for that is to set
336 ``error_idx`` to ``count`` if the validation failed. This has the
337 unfortunate side-effect that it is not possible to see which
338 control failed the validation. If the validation was successful
339 and the error happened while accessing the hardware, then
340 ``error_idx`` is less than ``count`` and only the controls up to
341 ``error_idx-1`` were read or written correctly, and the state of
342 the remaining controls is undefined.
344 Since :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` does not access hardware there is
345 also no need to handle the validation step in this special way, so
346 ``error_idx`` will just be set to the control that failed the
347 validation step instead of to ``count``. This means that if
348 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` fails with ``error_idx`` set to ``count``,
349 then you can call :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` to try to discover the
350 actual control that failed the validation step. Unfortunately,
351 there is no ``TRY`` equivalent for :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`.
359 - Reserved for future extensions.
361 Drivers and applications must set the array to zero.
365 - struct :ref:`v4l2_ext_control <v4l2-ext-control>` *
369 - Pointer to an array of ``count`` v4l2_ext_control structures.
371 Ignored if ``count`` equals zero.
374 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
378 .. flat-table:: Control classes
386 - ``V4L2_CTRL_CLASS_USER``
390 - The class containing user controls. These controls are described
391 in :ref:`control`. All controls that can be set using the
392 :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` and
393 :ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` ioctl belong to this
398 - ``V4L2_CTRL_CLASS_MPEG``
402 - The class containing MPEG compression controls. These controls are
403 described in :ref:`mpeg-controls`.
407 - ``V4L2_CTRL_CLASS_CAMERA``
411 - The class containing camera controls. These controls are described
412 in :ref:`camera-controls`.
416 - ``V4L2_CTRL_CLASS_FM_TX``
420 - The class containing FM Transmitter (FM TX) controls. These
421 controls are described in :ref:`fm-tx-controls`.
425 - ``V4L2_CTRL_CLASS_FLASH``
429 - The class containing flash device controls. These controls are
430 described in :ref:`flash-controls`.
434 - ``V4L2_CTRL_CLASS_JPEG``
438 - The class containing JPEG compression controls. These controls are
439 described in :ref:`jpeg-controls`.
443 - ``V4L2_CTRL_CLASS_IMAGE_SOURCE``
447 - The class containing image source controls. These controls are
448 described in :ref:`image-source-controls`.
452 - ``V4L2_CTRL_CLASS_IMAGE_PROC``
456 - The class containing image processing controls. These controls are
457 described in :ref:`image-process-controls`.
461 - ``V4L2_CTRL_CLASS_FM_RX``
465 - The class containing FM Receiver (FM RX) controls. These controls
466 are described in :ref:`fm-rx-controls`.
470 - ``V4L2_CTRL_CLASS_RF_TUNER``
474 - The class containing RF tuner controls. These controls are
475 described in :ref:`rf-tuner-controls`.
481 On success 0 is returned, on error -1 and the ``errno`` variable is set
482 appropriately. The generic error codes are described at the
483 :ref:`Generic Error Codes <gen-errors>` chapter.
486 The struct :ref:`v4l2_ext_control <v4l2-ext-control>` ``id`` is
487 invalid, the struct :ref:`v4l2_ext_controls <v4l2-ext-controls>`
488 ``which`` is invalid, or the struct
489 :ref:`v4l2_ext_control <v4l2-ext-control>` ``value`` was
490 inappropriate (e.g. the given menu index is not supported by the
491 driver). This error code is also returned by the
492 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` and :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctls if two or
493 more control values are in conflict.
496 The struct :ref:`v4l2_ext_control <v4l2-ext-control>` ``value``
500 The control is temporarily not changeable, possibly because another
501 applications took over control of the device function this control
505 The space reserved for the control's payload is insufficient. The
506 field ``size`` is set to a value that is enough to store the payload
507 and this error code is returned.
510 Attempt to try or set a read-only control or to get a write-only