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1 | .. -*- coding: utf-8; mode: rst -*- |
2 | ||
af4a4d0d | 3 | .. _VIDIOC_QUERYCTRL: |
5377d91f MH |
4 | |
5 | *************************************************************** | |
6 | ioctl VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL, VIDIOC_QUERYMENU | |
7 | *************************************************************** | |
8 | ||
9 | *man VIDIOC_QUERYCTRL(2)* | |
10 | ||
11 | VIDIOC_QUERY_EXT_CTRL | |
12 | VIDIOC_QUERYMENU | |
13 | Enumerate controls and menu control items | |
14 | ||
15 | ||
16 | Synopsis | |
17 | ======== | |
18 | ||
19 | .. c:function:: int ioctl( int fd, int request, struct v4l2_queryctrl *argp ) | |
20 | ||
21 | .. c:function:: int ioctl( int fd, int request, struct v4l2_query_ext_ctrl *argp ) | |
22 | ||
23 | .. c:function:: int ioctl( int fd, int request, struct v4l2_querymenu *argp ) | |
24 | ||
25 | Arguments | |
26 | ========= | |
27 | ||
28 | ``fd`` | |
29 | File descriptor returned by :ref:`open() <func-open>`. | |
30 | ||
31 | ``request`` | |
32 | VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL, VIDIOC_QUERYMENU | |
33 | ||
34 | ``argp`` | |
35 | ||
36 | ||
37 | Description | |
38 | =========== | |
39 | ||
40 | To query the attributes of a control applications set the ``id`` field | |
41 | of a struct :ref:`v4l2_queryctrl <v4l2-queryctrl>` and call the | |
42 | ``VIDIOC_QUERYCTRL`` ioctl with a pointer to this structure. The driver | |
43 | fills the rest of the structure or returns an EINVAL error code when the | |
44 | ``id`` is invalid. | |
45 | ||
46 | It is possible to enumerate controls by calling ``VIDIOC_QUERYCTRL`` | |
47 | with successive ``id`` values starting from ``V4L2_CID_BASE`` up to and | |
48 | exclusive ``V4L2_CID_LASTP1``. Drivers may return EINVAL if a control in | |
49 | this range is not supported. Further applications can enumerate private | |
50 | controls, which are not defined in this specification, by starting at | |
51 | ``V4L2_CID_PRIVATE_BASE`` and incrementing ``id`` until the driver | |
52 | returns EINVAL. | |
53 | ||
54 | In both cases, when the driver sets the ``V4L2_CTRL_FLAG_DISABLED`` flag | |
55 | in the ``flags`` field this control is permanently disabled and should | |
56 | be ignored by the application. [1]_ | |
57 | ||
58 | When the application ORs ``id`` with ``V4L2_CTRL_FLAG_NEXT_CTRL`` the | |
59 | driver returns the next supported non-compound control, or EINVAL if | |
60 | there is none. In addition, the ``V4L2_CTRL_FLAG_NEXT_COMPOUND`` flag | |
61 | can be specified to enumerate all compound controls (i.e. controls with | |
62 | type ≥ ``V4L2_CTRL_COMPOUND_TYPES`` and/or array control, in other words | |
63 | controls that contain more than one value). Specify both | |
64 | ``V4L2_CTRL_FLAG_NEXT_CTRL`` and ``V4L2_CTRL_FLAG_NEXT_COMPOUND`` in | |
65 | order to enumerate all controls, compound or not. Drivers which do not | |
66 | support these flags yet always return EINVAL. | |
67 | ||
68 | The ``VIDIOC_QUERY_EXT_CTRL`` ioctl was introduced in order to better | |
69 | support controls that can use compound types, and to expose additional | |
70 | control information that cannot be returned in struct | |
71 | :ref:`v4l2_queryctrl <v4l2-queryctrl>` since that structure is full. | |
72 | ||
73 | ``VIDIOC_QUERY_EXT_CTRL`` is used in the same way as | |
74 | ``VIDIOC_QUERYCTRL``, except that the ``reserved`` array must be zeroed | |
75 | as well. | |
76 | ||
77 | Additional information is required for menu controls: the names of the | |
78 | menu items. To query them applications set the ``id`` and ``index`` | |
79 | fields of struct :ref:`v4l2_querymenu <v4l2-querymenu>` and call the | |
80 | ``VIDIOC_QUERYMENU`` ioctl with a pointer to this structure. The driver | |
81 | fills the rest of the structure or returns an EINVAL error code when the | |
82 | ``id`` or ``index`` is invalid. Menu items are enumerated by calling | |
83 | ``VIDIOC_QUERYMENU`` with successive ``index`` values from struct | |
84 | :ref:`v4l2_queryctrl <v4l2-queryctrl>` ``minimum`` to ``maximum``, | |
85 | inclusive. Note that it is possible for ``VIDIOC_QUERYMENU`` to return | |
86 | an EINVAL error code for some indices between ``minimum`` and | |
87 | ``maximum``. In that case that particular menu item is not supported by | |
88 | this driver. Also note that the ``minimum`` value is not necessarily 0. | |
89 | ||
90 | See also the examples in :ref:`control`. | |
91 | ||
92 | ||
93 | .. _v4l2-queryctrl: | |
94 | ||
95 | .. flat-table:: struct v4l2_queryctrl | |
96 | :header-rows: 0 | |
97 | :stub-columns: 0 | |
98 | :widths: 1 1 2 | |
99 | ||
100 | ||
101 | - .. row 1 | |
102 | ||
103 | - __u32 | |
104 | ||
105 | - ``id`` | |
106 | ||
107 | - Identifies the control, set by the application. See | |
108 | :ref:`control-id` for predefined IDs. When the ID is ORed with | |
109 | V4L2_CTRL_FLAG_NEXT_CTRL the driver clears the flag and | |
110 | returns the first control with a higher ID. Drivers which do not | |
111 | support this flag yet always return an EINVAL error code. | |
112 | ||
113 | - .. row 2 | |
114 | ||
115 | - __u32 | |
116 | ||
117 | - ``type`` | |
118 | ||
119 | - Type of control, see :ref:`v4l2-ctrl-type`. | |
120 | ||
121 | - .. row 3 | |
122 | ||
123 | - __u8 | |
124 | ||
125 | - ``name``\ [32] | |
126 | ||
127 | - Name of the control, a NUL-terminated ASCII string. This | |
128 | information is intended for the user. | |
129 | ||
130 | - .. row 4 | |
131 | ||
132 | - __s32 | |
133 | ||
134 | - ``minimum`` | |
135 | ||
136 | - Minimum value, inclusive. This field gives a lower bound for the | |
137 | control. See enum :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how | |
138 | the minimum value is to be used for each possible control type. | |
139 | Note that this a signed 32-bit value. | |
140 | ||
141 | - .. row 5 | |
142 | ||
143 | - __s32 | |
144 | ||
145 | - ``maximum`` | |
146 | ||
147 | - Maximum value, inclusive. This field gives an upper bound for the | |
148 | control. See enum :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how | |
149 | the maximum value is to be used for each possible control type. | |
150 | Note that this a signed 32-bit value. | |
151 | ||
152 | - .. row 6 | |
153 | ||
154 | - __s32 | |
155 | ||
156 | - ``step`` | |
157 | ||
158 | - This field gives a step size for the control. See enum | |
159 | :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how the step value is | |
160 | to be used for each possible control type. Note that this an | |
161 | unsigned 32-bit value. | |
162 | ||
163 | Generally drivers should not scale hardware control values. It may | |
164 | be necessary for example when the ``name`` or ``id`` imply a | |
165 | particular unit and the hardware actually accepts only multiples | |
166 | of said unit. If so, drivers must take care values are properly | |
167 | rounded when scaling, such that errors will not accumulate on | |
168 | repeated read-write cycles. | |
169 | ||
170 | This field gives the smallest change of an integer control | |
171 | actually affecting hardware. Often the information is needed when | |
172 | the user can change controls by keyboard or GUI buttons, rather | |
173 | than a slider. When for example a hardware register accepts values | |
174 | 0-511 and the driver reports 0-65535, step should be 128. | |
175 | ||
176 | Note that although signed, the step value is supposed to be always | |
177 | positive. | |
178 | ||
179 | - .. row 7 | |
180 | ||
181 | - __s32 | |
182 | ||
183 | - ``default_value`` | |
184 | ||
185 | - The default value of a ``V4L2_CTRL_TYPE_INTEGER``, ``_BOOLEAN``, | |
186 | ``_BITMASK``, ``_MENU`` or ``_INTEGER_MENU`` control. Not valid | |
187 | for other types of controls. Note that drivers reset controls to | |
188 | their default value only when the driver is first loaded, never | |
189 | afterwards. | |
190 | ||
191 | - .. row 8 | |
192 | ||
193 | - __u32 | |
194 | ||
195 | - ``flags`` | |
196 | ||
197 | - Control flags, see :ref:`control-flags`. | |
198 | ||
199 | - .. row 9 | |
200 | ||
201 | - __u32 | |
202 | ||
203 | - ``reserved``\ [2] | |
204 | ||
205 | - Reserved for future extensions. Drivers must set the array to | |
206 | zero. | |
207 | ||
208 | ||
209 | ||
210 | .. _v4l2-query-ext-ctrl: | |
211 | ||
212 | .. flat-table:: struct v4l2_query_ext_ctrl | |
213 | :header-rows: 0 | |
214 | :stub-columns: 0 | |
215 | :widths: 1 1 2 | |
216 | ||
217 | ||
218 | - .. row 1 | |
219 | ||
220 | - __u32 | |
221 | ||
222 | - ``id`` | |
223 | ||
224 | - Identifies the control, set by the application. See | |
225 | :ref:`control-id` for predefined IDs. When the ID is ORed with | |
226 | ``V4L2_CTRL_FLAG_NEXT_CTRL`` the driver clears the flag and | |
227 | returns the first non-compound control with a higher ID. When the | |
228 | ID is ORed with ``V4L2_CTRL_FLAG_NEXT_COMPOUND`` the driver clears | |
229 | the flag and returns the first compound control with a higher ID. | |
230 | Set both to get the first control (compound or not) with a higher | |
231 | ID. | |
232 | ||
233 | - .. row 2 | |
234 | ||
235 | - __u32 | |
236 | ||
237 | - ``type`` | |
238 | ||
239 | - Type of control, see :ref:`v4l2-ctrl-type`. | |
240 | ||
241 | - .. row 3 | |
242 | ||
243 | - char | |
244 | ||
245 | - ``name``\ [32] | |
246 | ||
247 | - Name of the control, a NUL-terminated ASCII string. This | |
248 | information is intended for the user. | |
249 | ||
250 | - .. row 4 | |
251 | ||
252 | - __s64 | |
253 | ||
254 | - ``minimum`` | |
255 | ||
256 | - Minimum value, inclusive. This field gives a lower bound for the | |
257 | control. See enum :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how | |
258 | the minimum value is to be used for each possible control type. | |
259 | Note that this a signed 64-bit value. | |
260 | ||
261 | - .. row 5 | |
262 | ||
263 | - __s64 | |
264 | ||
265 | - ``maximum`` | |
266 | ||
267 | - Maximum value, inclusive. This field gives an upper bound for the | |
268 | control. See enum :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how | |
269 | the maximum value is to be used for each possible control type. | |
270 | Note that this a signed 64-bit value. | |
271 | ||
272 | - .. row 6 | |
273 | ||
274 | - __u64 | |
275 | ||
276 | - ``step`` | |
277 | ||
278 | - This field gives a step size for the control. See enum | |
279 | :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how the step value is | |
280 | to be used for each possible control type. Note that this an | |
281 | unsigned 64-bit value. | |
282 | ||
283 | Generally drivers should not scale hardware control values. It may | |
284 | be necessary for example when the ``name`` or ``id`` imply a | |
285 | particular unit and the hardware actually accepts only multiples | |
286 | of said unit. If so, drivers must take care values are properly | |
287 | rounded when scaling, such that errors will not accumulate on | |
288 | repeated read-write cycles. | |
289 | ||
290 | This field gives the smallest change of an integer control | |
291 | actually affecting hardware. Often the information is needed when | |
292 | the user can change controls by keyboard or GUI buttons, rather | |
293 | than a slider. When for example a hardware register accepts values | |
294 | 0-511 and the driver reports 0-65535, step should be 128. | |
295 | ||
296 | - .. row 7 | |
297 | ||
298 | - __s64 | |
299 | ||
300 | - ``default_value`` | |
301 | ||
302 | - The default value of a ``V4L2_CTRL_TYPE_INTEGER``, ``_INTEGER64``, | |
303 | ``_BOOLEAN``, ``_BITMASK``, ``_MENU``, ``_INTEGER_MENU``, ``_U8`` | |
304 | or ``_U16`` control. Not valid for other types of controls. Note | |
305 | that drivers reset controls to their default value only when the | |
306 | driver is first loaded, never afterwards. | |
307 | ||
308 | - .. row 8 | |
309 | ||
310 | - __u32 | |
311 | ||
312 | - ``flags`` | |
313 | ||
314 | - Control flags, see :ref:`control-flags`. | |
315 | ||
316 | - .. row 9 | |
317 | ||
318 | - __u32 | |
319 | ||
320 | - ``elem_size`` | |
321 | ||
322 | - The size in bytes of a single element of the array. Given a char | |
323 | pointer ``p`` to a 3-dimensional array you can find the position | |
324 | of cell ``(z, y, x)`` as follows: | |
325 | ``p + ((z * dims[1] + y) * dims[0] + x) * elem_size``. | |
326 | ``elem_size`` is always valid, also when the control isn't an | |
327 | array. For string controls ``elem_size`` is equal to | |
328 | ``maximum + 1``. | |
329 | ||
330 | - .. row 10 | |
331 | ||
332 | - __u32 | |
333 | ||
334 | - ``elems`` | |
335 | ||
336 | - The number of elements in the N-dimensional array. If this control | |
337 | is not an array, then ``elems`` is 1. The ``elems`` field can | |
338 | never be 0. | |
339 | ||
340 | - .. row 11 | |
341 | ||
342 | - __u32 | |
343 | ||
344 | - ``nr_of_dims`` | |
345 | ||
346 | - The number of dimension in the N-dimensional array. If this | |
347 | control is not an array, then this field is 0. | |
348 | ||
349 | - .. row 12 | |
350 | ||
351 | - __u32 | |
352 | ||
353 | - ``dims[V4L2_CTRL_MAX_DIMS]`` | |
354 | ||
355 | - The size of each dimension. The first ``nr_of_dims`` elements of | |
356 | this array must be non-zero, all remaining elements must be zero. | |
357 | ||
358 | - .. row 13 | |
359 | ||
360 | - __u32 | |
361 | ||
362 | - ``reserved``\ [32] | |
363 | ||
364 | - Reserved for future extensions. Applications and drivers must set | |
365 | the array to zero. | |
366 | ||
367 | ||
368 | ||
369 | .. _v4l2-querymenu: | |
370 | ||
371 | .. flat-table:: struct v4l2_querymenu | |
372 | :header-rows: 0 | |
373 | :stub-columns: 0 | |
374 | :widths: 1 1 2 1 | |
375 | ||
376 | ||
377 | - .. row 1 | |
378 | ||
379 | - __u32 | |
380 | ||
381 | - | |
382 | - ``id`` | |
383 | ||
384 | - Identifies the control, set by the application from the respective | |
385 | struct :ref:`v4l2_queryctrl <v4l2-queryctrl>` ``id``. | |
386 | ||
387 | - .. row 2 | |
388 | ||
389 | - __u32 | |
390 | ||
391 | - | |
392 | - ``index`` | |
393 | ||
394 | - Index of the menu item, starting at zero, set by the application. | |
395 | ||
396 | - .. row 3 | |
397 | ||
398 | - union | |
399 | ||
400 | - | |
401 | - | |
402 | - | |
403 | ||
404 | - .. row 4 | |
405 | ||
406 | - | |
407 | - __u8 | |
408 | ||
409 | - ``name``\ [32] | |
410 | ||
411 | - Name of the menu item, a NUL-terminated ASCII string. This | |
412 | information is intended for the user. This field is valid for | |
413 | ``V4L2_CTRL_FLAG_MENU`` type controls. | |
414 | ||
415 | - .. row 5 | |
416 | ||
417 | - | |
418 | - __s64 | |
419 | ||
420 | - ``value`` | |
421 | ||
422 | - Value of the integer menu item. This field is valid for | |
423 | ``V4L2_CTRL_FLAG_INTEGER_MENU`` type controls. | |
424 | ||
425 | - .. row 6 | |
426 | ||
427 | - __u32 | |
428 | ||
429 | - | |
430 | - ``reserved`` | |
431 | ||
432 | - Reserved for future extensions. Drivers must set the array to | |
433 | zero. | |
434 | ||
435 | ||
436 | ||
437 | .. _v4l2-ctrl-type: | |
438 | ||
439 | .. flat-table:: enum v4l2_ctrl_type | |
440 | :header-rows: 1 | |
441 | :stub-columns: 0 | |
442 | :widths: 30 5 5 5 55 | |
443 | ||
444 | ||
445 | - .. row 1 | |
446 | ||
447 | - Type | |
448 | ||
449 | - ``minimum`` | |
450 | ||
451 | - ``step`` | |
452 | ||
453 | - ``maximum`` | |
454 | ||
455 | - Description | |
456 | ||
457 | - .. row 2 | |
458 | ||
459 | - ``V4L2_CTRL_TYPE_INTEGER`` | |
460 | ||
461 | - any | |
462 | ||
463 | - any | |
464 | ||
465 | - any | |
466 | ||
467 | - An integer-valued control ranging from minimum to maximum | |
468 | inclusive. The step value indicates the increment between values. | |
469 | ||
470 | - .. row 3 | |
471 | ||
472 | - ``V4L2_CTRL_TYPE_BOOLEAN`` | |
473 | ||
474 | - 0 | |
475 | ||
476 | - 1 | |
477 | ||
478 | - 1 | |
479 | ||
480 | - A boolean-valued control. Zero corresponds to "disabled", and one | |
481 | means "enabled". | |
482 | ||
483 | - .. row 4 | |
484 | ||
485 | - ``V4L2_CTRL_TYPE_MENU`` | |
486 | ||
487 | - ≥ 0 | |
488 | ||
489 | - 1 | |
490 | ||
491 | - N-1 | |
492 | ||
493 | - The control has a menu of N choices. The names of the menu items | |
494 | can be enumerated with the ``VIDIOC_QUERYMENU`` ioctl. | |
495 | ||
496 | - .. row 5 | |
497 | ||
498 | - ``V4L2_CTRL_TYPE_INTEGER_MENU`` | |
499 | ||
500 | - ≥ 0 | |
501 | ||
502 | - 1 | |
503 | ||
504 | - N-1 | |
505 | ||
506 | - The control has a menu of N choices. The values of the menu items | |
507 | can be enumerated with the ``VIDIOC_QUERYMENU`` ioctl. This is | |
508 | similar to ``V4L2_CTRL_TYPE_MENU`` except that instead of strings, | |
509 | the menu items are signed 64-bit integers. | |
510 | ||
511 | - .. row 6 | |
512 | ||
513 | - ``V4L2_CTRL_TYPE_BITMASK`` | |
514 | ||
515 | - 0 | |
516 | ||
517 | - n/a | |
518 | ||
519 | - any | |
520 | ||
521 | - A bitmask field. The maximum value is the set of bits that can be | |
522 | used, all other bits are to be 0. The maximum value is interpreted | |
523 | as a __u32, allowing the use of bit 31 in the bitmask. | |
524 | ||
525 | - .. row 7 | |
526 | ||
527 | - ``V4L2_CTRL_TYPE_BUTTON`` | |
528 | ||
529 | - 0 | |
530 | ||
531 | - 0 | |
532 | ||
533 | - 0 | |
534 | ||
535 | - A control which performs an action when set. Drivers must ignore | |
536 | the value passed with ``VIDIOC_S_CTRL`` and return an EINVAL error | |
537 | code on a ``VIDIOC_G_CTRL`` attempt. | |
538 | ||
539 | - .. row 8 | |
540 | ||
541 | - ``V4L2_CTRL_TYPE_INTEGER64`` | |
542 | ||
543 | - any | |
544 | ||
545 | - any | |
546 | ||
547 | - any | |
548 | ||
549 | - A 64-bit integer valued control. Minimum, maximum and step size | |
550 | cannot be queried using ``VIDIOC_QUERYCTRL``. Only | |
551 | ``VIDIOC_QUERY_EXT_CTRL`` can retrieve the 64-bit min/max/step | |
552 | values, they should be interpreted as n/a when using | |
553 | ``VIDIOC_QUERYCTRL``. | |
554 | ||
555 | - .. row 9 | |
556 | ||
557 | - ``V4L2_CTRL_TYPE_STRING`` | |
558 | ||
559 | - ≥ 0 | |
560 | ||
561 | - ≥ 1 | |
562 | ||
563 | - ≥ 0 | |
564 | ||
565 | - The minimum and maximum string lengths. The step size means that | |
566 | the string must be (minimum + N * step) characters long for N ≥ 0. | |
567 | These lengths do not include the terminating zero, so in order to | |
568 | pass a string of length 8 to | |
af4a4d0d | 569 | :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` you need to |
5377d91f MH |
570 | set the ``size`` field of struct |
571 | :ref:`v4l2_ext_control <v4l2-ext-control>` to 9. For | |
af4a4d0d | 572 | :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` you can set |
5377d91f MH |
573 | the ``size`` field to ``maximum`` + 1. Which character encoding is |
574 | used will depend on the string control itself and should be part | |
575 | of the control documentation. | |
576 | ||
577 | - .. row 10 | |
578 | ||
579 | - ``V4L2_CTRL_TYPE_CTRL_CLASS`` | |
580 | ||
581 | - n/a | |
582 | ||
583 | - n/a | |
584 | ||
585 | - n/a | |
586 | ||
587 | - This is not a control. When ``VIDIOC_QUERYCTRL`` is called with a | |
588 | control ID equal to a control class code (see :ref:`ctrl-class`) | |
589 | + 1, the ioctl returns the name of the control class and this | |
590 | control type. Older drivers which do not support this feature | |
591 | return an EINVAL error code. | |
592 | ||
593 | - .. row 11 | |
594 | ||
595 | - ``V4L2_CTRL_TYPE_U8`` | |
596 | ||
597 | - any | |
598 | ||
599 | - any | |
600 | ||
601 | - any | |
602 | ||
603 | - An unsigned 8-bit valued control ranging from minimum to maximum | |
604 | inclusive. The step value indicates the increment between values. | |
605 | ||
606 | - .. row 12 | |
607 | ||
608 | - ``V4L2_CTRL_TYPE_U16`` | |
609 | ||
610 | - any | |
611 | ||
612 | - any | |
613 | ||
614 | - any | |
615 | ||
616 | - An unsigned 16-bit valued control ranging from minimum to maximum | |
617 | inclusive. The step value indicates the increment between values. | |
618 | ||
619 | - .. row 13 | |
620 | ||
621 | - ``V4L2_CTRL_TYPE_U32`` | |
622 | ||
623 | - any | |
624 | ||
625 | - any | |
626 | ||
627 | - any | |
628 | ||
629 | - An unsigned 32-bit valued control ranging from minimum to maximum | |
630 | inclusive. The step value indicates the increment between values. | |
631 | ||
632 | ||
633 | ||
634 | .. _control-flags: | |
635 | ||
636 | .. flat-table:: Control Flags | |
637 | :header-rows: 0 | |
638 | :stub-columns: 0 | |
639 | :widths: 3 1 4 | |
640 | ||
641 | ||
642 | - .. row 1 | |
643 | ||
644 | - ``V4L2_CTRL_FLAG_DISABLED`` | |
645 | ||
646 | - 0x0001 | |
647 | ||
648 | - This control is permanently disabled and should be ignored by the | |
649 | application. Any attempt to change the control will result in an | |
650 | EINVAL error code. | |
651 | ||
652 | - .. row 2 | |
653 | ||
654 | - ``V4L2_CTRL_FLAG_GRABBED`` | |
655 | ||
656 | - 0x0002 | |
657 | ||
658 | - This control is temporarily unchangeable, for example because | |
659 | another application took over control of the respective resource. | |
660 | Such controls may be displayed specially in a user interface. | |
661 | Attempts to change the control may result in an EBUSY error code. | |
662 | ||
663 | - .. row 3 | |
664 | ||
665 | - ``V4L2_CTRL_FLAG_READ_ONLY`` | |
666 | ||
667 | - 0x0004 | |
668 | ||
669 | - This control is permanently readable only. Any attempt to change | |
670 | the control will result in an EINVAL error code. | |
671 | ||
672 | - .. row 4 | |
673 | ||
674 | - ``V4L2_CTRL_FLAG_UPDATE`` | |
675 | ||
676 | - 0x0008 | |
677 | ||
678 | - A hint that changing this control may affect the value of other | |
679 | controls within the same control class. Applications should update | |
680 | their user interface accordingly. | |
681 | ||
682 | - .. row 5 | |
683 | ||
684 | - ``V4L2_CTRL_FLAG_INACTIVE`` | |
685 | ||
686 | - 0x0010 | |
687 | ||
688 | - This control is not applicable to the current configuration and | |
689 | should be displayed accordingly in a user interface. For example | |
690 | the flag may be set on a MPEG audio level 2 bitrate control when | |
691 | MPEG audio encoding level 1 was selected with another control. | |
692 | ||
693 | - .. row 6 | |
694 | ||
695 | - ``V4L2_CTRL_FLAG_SLIDER`` | |
696 | ||
697 | - 0x0020 | |
698 | ||
699 | - A hint that this control is best represented as a slider-like | |
700 | element in a user interface. | |
701 | ||
702 | - .. row 7 | |
703 | ||
704 | - ``V4L2_CTRL_FLAG_WRITE_ONLY`` | |
705 | ||
706 | - 0x0040 | |
707 | ||
708 | - This control is permanently writable only. Any attempt to read the | |
709 | control will result in an EACCES error code error code. This flag | |
710 | is typically present for relative controls or action controls | |
711 | where writing a value will cause the device to carry out a given | |
712 | action (e. g. motor control) but no meaningful value can be | |
713 | returned. | |
714 | ||
715 | - .. row 8 | |
716 | ||
717 | - ``V4L2_CTRL_FLAG_VOLATILE`` | |
718 | ||
719 | - 0x0080 | |
720 | ||
721 | - This control is volatile, which means that the value of the | |
722 | control changes continuously. A typical example would be the | |
723 | current gain value if the device is in auto-gain mode. In such a | |
724 | case the hardware calculates the gain value based on the lighting | |
725 | conditions which can change over time. Note that setting a new | |
726 | value for a volatile control will have no effect and no | |
727 | ``V4L2_EVENT_CTRL_CH_VALUE`` will be sent, unless the | |
728 | ``V4L2_CTRL_FLAG_EXECUTE_ON_WRITE`` flag (see below) is also set. | |
729 | Otherwise the new value will just be ignored. | |
730 | ||
731 | - .. row 9 | |
732 | ||
733 | - ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` | |
734 | ||
735 | - 0x0100 | |
736 | ||
737 | - This control has a pointer type, so its value has to be accessed | |
738 | using one of the pointer fields of struct | |
739 | :ref:`v4l2_ext_control <v4l2-ext-control>`. This flag is set | |
740 | for controls that are an array, string, or have a compound type. | |
741 | In all cases you have to set a pointer to memory containing the | |
742 | payload of the control. | |
743 | ||
744 | - .. row 10 | |
745 | ||
746 | - ``V4L2_CTRL_FLAG_EXECUTE_ON_WRITE`` | |
747 | ||
748 | - 0x0200 | |
749 | ||
750 | - The value provided to the control will be propagated to the driver | |
751 | even if it remains constant. This is required when the control | |
752 | represents an action on the hardware. For example: clearing an | |
753 | error flag or triggering the flash. All the controls of the type | |
754 | ``V4L2_CTRL_TYPE_BUTTON`` have this flag set. | |
755 | ||
756 | ||
757 | ||
758 | Return Value | |
759 | ============ | |
760 | ||
761 | On success 0 is returned, on error -1 and the ``errno`` variable is set | |
762 | appropriately. The generic error codes are described at the | |
763 | :ref:`Generic Error Codes <gen-errors>` chapter. | |
764 | ||
765 | EINVAL | |
766 | The struct :ref:`v4l2_queryctrl <v4l2-queryctrl>` ``id`` is | |
767 | invalid. The struct :ref:`v4l2_querymenu <v4l2-querymenu>` ``id`` | |
768 | is invalid or ``index`` is out of range (less than ``minimum`` or | |
769 | greater than ``maximum``) or this particular menu item is not | |
770 | supported by the driver. | |
771 | ||
772 | EACCES | |
773 | An attempt was made to read a write-only control. | |
774 | ||
775 | .. [1] | |
776 | ``V4L2_CTRL_FLAG_DISABLED`` was intended for two purposes: Drivers | |
777 | can skip predefined controls not supported by the hardware (although | |
778 | returning EINVAL would do as well), or disable predefined and private | |
779 | controls after hardware detection without the trouble of reordering | |
780 | control arrays and indices (EINVAL cannot be used to skip private | |
781 | controls because it would prematurely end the enumeration). | |
782 | ||
783 | ||
784 | .. ------------------------------------------------------------------------------ | |
785 | .. This file was automatically converted from DocBook-XML with the dbxml | |
786 | .. library (https://github.com/return42/sphkerneldoc). The origin XML comes | |
787 | .. from the linux kernel, refer to: | |
788 | .. | |
789 | .. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook | |
790 | .. ------------------------------------------------------------------------------ |