1 .. -*- coding: utf-8; mode: rst -*-
5 *******************************************************************
6 ioctls VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL and VIDIOC_QUERYMENU
7 *******************************************************************
12 VIDIOC_QUERYCTRL - VIDIOC_QUERY_EXT_CTRL - VIDIOC_QUERYMENU - Enumerate controls and menu control items
18 .. cpp:function:: int ioctl( int fd, int request, struct v4l2_queryctrl *argp )
20 .. cpp:function:: int ioctl( int fd, int request, struct v4l2_query_ext_ctrl *argp )
22 .. cpp:function:: int ioctl( int fd, int request, struct v4l2_querymenu *argp )
29 File descriptor returned by :ref:`open() <func-open>`.
32 VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL, VIDIOC_QUERYMENU
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
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
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. [#f1]_
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``.
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.
73 ``VIDIOC_QUERY_EXT_CTRL`` is used in the same way as
74 ``VIDIOC_QUERYCTRL``, except that the ``reserved`` array must be zeroed
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``,
89 It is possible for ``VIDIOC_QUERYMENU`` to return
90 an ``EINVAL`` error code for some indices between ``minimum`` and
91 ``maximum``. In that case that particular menu item is not supported by
92 this driver. Also note that the ``minimum`` value is not necessarily 0.
94 See also the examples in :ref:`control`.
99 .. flat-table:: struct v4l2_queryctrl
111 - Identifies the control, set by the application. See
112 :ref:`control-id` for predefined IDs. When the ID is ORed with
113 V4L2_CTRL_FLAG_NEXT_CTRL the driver clears the flag and
114 returns the first control with a higher ID. Drivers which do not
115 support this flag yet always return an ``EINVAL`` error code.
123 - Type of control, see :ref:`v4l2-ctrl-type`.
131 - Name of the control, a NUL-terminated ASCII string. This
132 information is intended for the user.
140 - Minimum value, inclusive. This field gives a lower bound for the
141 control. See enum :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how
142 the minimum value is to be used for each possible control type.
143 Note that this a signed 32-bit value.
151 - Maximum value, inclusive. This field gives an upper bound for the
152 control. See enum :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how
153 the maximum value is to be used for each possible control type.
154 Note that this a signed 32-bit value.
162 - This field gives a step size for the control. See enum
163 :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how the step value is
164 to be used for each possible control type. Note that this an
165 unsigned 32-bit value.
167 Generally drivers should not scale hardware control values. It may
168 be necessary for example when the ``name`` or ``id`` imply a
169 particular unit and the hardware actually accepts only multiples
170 of said unit. If so, drivers must take care values are properly
171 rounded when scaling, such that errors will not accumulate on
172 repeated read-write cycles.
174 This field gives the smallest change of an integer control
175 actually affecting hardware. Often the information is needed when
176 the user can change controls by keyboard or GUI buttons, rather
177 than a slider. When for example a hardware register accepts values
178 0-511 and the driver reports 0-65535, step should be 128.
180 Note that although signed, the step value is supposed to be always
189 - The default value of a ``V4L2_CTRL_TYPE_INTEGER``, ``_BOOLEAN``,
190 ``_BITMASK``, ``_MENU`` or ``_INTEGER_MENU`` control. Not valid
191 for other types of controls.
195 Drivers reset controls to their default value only when
196 the driver is first loaded, never afterwards.
204 - Control flags, see :ref:`control-flags`.
212 - Reserved for future extensions. Drivers must set the array to
217 .. _v4l2-query-ext-ctrl:
219 .. flat-table:: struct v4l2_query_ext_ctrl
231 - Identifies the control, set by the application. See
232 :ref:`control-id` for predefined IDs. When the ID is ORed with
233 ``V4L2_CTRL_FLAG_NEXT_CTRL`` the driver clears the flag and
234 returns the first non-compound control with a higher ID. When the
235 ID is ORed with ``V4L2_CTRL_FLAG_NEXT_COMPOUND`` the driver clears
236 the flag and returns the first compound control with a higher ID.
237 Set both to get the first control (compound or not) with a higher
246 - Type of control, see :ref:`v4l2-ctrl-type`.
254 - Name of the control, a NUL-terminated ASCII string. This
255 information is intended for the user.
263 - Minimum value, inclusive. This field gives a lower bound for the
264 control. See enum :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how
265 the minimum value is to be used for each possible control type.
266 Note that this a signed 64-bit value.
274 - Maximum value, inclusive. This field gives an upper bound for the
275 control. See enum :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how
276 the maximum value is to be used for each possible control type.
277 Note that this a signed 64-bit value.
285 - This field gives a step size for the control. See enum
286 :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how the step value is
287 to be used for each possible control type. Note that this an
288 unsigned 64-bit value.
290 Generally drivers should not scale hardware control values. It may
291 be necessary for example when the ``name`` or ``id`` imply a
292 particular unit and the hardware actually accepts only multiples
293 of said unit. If so, drivers must take care values are properly
294 rounded when scaling, such that errors will not accumulate on
295 repeated read-write cycles.
297 This field gives the smallest change of an integer control
298 actually affecting hardware. Often the information is needed when
299 the user can change controls by keyboard or GUI buttons, rather
300 than a slider. When for example a hardware register accepts values
301 0-511 and the driver reports 0-65535, step should be 128.
309 - The default value of a ``V4L2_CTRL_TYPE_INTEGER``, ``_INTEGER64``,
310 ``_BOOLEAN``, ``_BITMASK``, ``_MENU``, ``_INTEGER_MENU``, ``_U8``
311 or ``_U16`` control. Not valid for other types of controls.
315 Drivers reset controls to their default value only when
316 the driver is first loaded, never afterwards.
324 - Control flags, see :ref:`control-flags`.
332 - The size in bytes of a single element of the array. Given a char
333 pointer ``p`` to a 3-dimensional array you can find the position
334 of cell ``(z, y, x)`` as follows:
335 ``p + ((z * dims[1] + y) * dims[0] + x) * elem_size``.
336 ``elem_size`` is always valid, also when the control isn't an
337 array. For string controls ``elem_size`` is equal to
346 - The number of elements in the N-dimensional array. If this control
347 is not an array, then ``elems`` is 1. The ``elems`` field can
356 - The number of dimension in the N-dimensional array. If this
357 control is not an array, then this field is 0.
363 - ``dims[V4L2_CTRL_MAX_DIMS]``
365 - The size of each dimension. The first ``nr_of_dims`` elements of
366 this array must be non-zero, all remaining elements must be zero.
374 - Reserved for future extensions. Applications and drivers must set
381 .. flat-table:: struct v4l2_querymenu
394 - Identifies the control, set by the application from the respective
395 struct :ref:`v4l2_queryctrl <v4l2-queryctrl>` ``id``.
404 - Index of the menu item, starting at zero, set by the application.
421 - Name of the menu item, a NUL-terminated ASCII string. This
422 information is intended for the user. This field is valid for
423 ``V4L2_CTRL_FLAG_MENU`` type controls.
432 - Value of the integer menu item. This field is valid for
433 ``V4L2_CTRL_FLAG_INTEGER_MENU`` type controls.
442 - Reserved for future extensions. Drivers must set the array to
449 .. flat-table:: enum v4l2_ctrl_type
469 - ``V4L2_CTRL_TYPE_INTEGER``
477 - An integer-valued control ranging from minimum to maximum
478 inclusive. The step value indicates the increment between values.
482 - ``V4L2_CTRL_TYPE_BOOLEAN``
490 - A boolean-valued control. Zero corresponds to "disabled", and one
495 - ``V4L2_CTRL_TYPE_MENU``
503 - The control has a menu of N choices. The names of the menu items
504 can be enumerated with the ``VIDIOC_QUERYMENU`` ioctl.
508 - ``V4L2_CTRL_TYPE_INTEGER_MENU``
516 - The control has a menu of N choices. The values of the menu items
517 can be enumerated with the ``VIDIOC_QUERYMENU`` ioctl. This is
518 similar to ``V4L2_CTRL_TYPE_MENU`` except that instead of strings,
519 the menu items are signed 64-bit integers.
523 - ``V4L2_CTRL_TYPE_BITMASK``
531 - A bitmask field. The maximum value is the set of bits that can be
532 used, all other bits are to be 0. The maximum value is interpreted
533 as a __u32, allowing the use of bit 31 in the bitmask.
537 - ``V4L2_CTRL_TYPE_BUTTON``
545 - A control which performs an action when set. Drivers must ignore
546 the value passed with ``VIDIOC_S_CTRL`` and return an ``EINVAL`` error
547 code on a ``VIDIOC_G_CTRL`` attempt.
551 - ``V4L2_CTRL_TYPE_INTEGER64``
559 - A 64-bit integer valued control. Minimum, maximum and step size
560 cannot be queried using ``VIDIOC_QUERYCTRL``. Only
561 ``VIDIOC_QUERY_EXT_CTRL`` can retrieve the 64-bit min/max/step
562 values, they should be interpreted as n/a when using
563 ``VIDIOC_QUERYCTRL``.
567 - ``V4L2_CTRL_TYPE_STRING``
575 - The minimum and maximum string lengths. The step size means that
576 the string must be (minimum + N * step) characters long for N ≥ 0.
577 These lengths do not include the terminating zero, so in order to
578 pass a string of length 8 to
579 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` you need to
580 set the ``size`` field of struct
581 :ref:`v4l2_ext_control <v4l2-ext-control>` to 9. For
582 :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` you can set
583 the ``size`` field to ``maximum`` + 1. Which character encoding is
584 used will depend on the string control itself and should be part
585 of the control documentation.
589 - ``V4L2_CTRL_TYPE_CTRL_CLASS``
597 - This is not a control. When ``VIDIOC_QUERYCTRL`` is called with a
598 control ID equal to a control class code (see :ref:`ctrl-class`)
599 + 1, the ioctl returns the name of the control class and this
600 control type. Older drivers which do not support this feature
601 return an ``EINVAL`` error code.
605 - ``V4L2_CTRL_TYPE_U8``
613 - An unsigned 8-bit valued control ranging from minimum to maximum
614 inclusive. The step value indicates the increment between values.
618 - ``V4L2_CTRL_TYPE_U16``
626 - An unsigned 16-bit valued control ranging from minimum to maximum
627 inclusive. The step value indicates the increment between values.
631 - ``V4L2_CTRL_TYPE_U32``
639 - An unsigned 32-bit valued control ranging from minimum to maximum
640 inclusive. The step value indicates the increment between values.
646 .. flat-table:: Control Flags
654 - ``V4L2_CTRL_FLAG_DISABLED``
658 - This control is permanently disabled and should be ignored by the
659 application. Any attempt to change the control will result in an
660 ``EINVAL`` error code.
664 - ``V4L2_CTRL_FLAG_GRABBED``
668 - This control is temporarily unchangeable, for example because
669 another application took over control of the respective resource.
670 Such controls may be displayed specially in a user interface.
671 Attempts to change the control may result in an ``EBUSY`` error code.
675 - ``V4L2_CTRL_FLAG_READ_ONLY``
679 - This control is permanently readable only. Any attempt to change
680 the control will result in an ``EINVAL`` error code.
684 - ``V4L2_CTRL_FLAG_UPDATE``
688 - A hint that changing this control may affect the value of other
689 controls within the same control class. Applications should update
690 their user interface accordingly.
694 - ``V4L2_CTRL_FLAG_INACTIVE``
698 - This control is not applicable to the current configuration and
699 should be displayed accordingly in a user interface. For example
700 the flag may be set on a MPEG audio level 2 bitrate control when
701 MPEG audio encoding level 1 was selected with another control.
705 - ``V4L2_CTRL_FLAG_SLIDER``
709 - A hint that this control is best represented as a slider-like
710 element in a user interface.
714 - ``V4L2_CTRL_FLAG_WRITE_ONLY``
718 - This control is permanently writable only. Any attempt to read the
719 control will result in an ``EACCES`` error code error code. This flag
720 is typically present for relative controls or action controls
721 where writing a value will cause the device to carry out a given
722 action (e. g. motor control) but no meaningful value can be
727 - ``V4L2_CTRL_FLAG_VOLATILE``
731 - This control is volatile, which means that the value of the
732 control changes continuously. A typical example would be the
733 current gain value if the device is in auto-gain mode. In such a
734 case the hardware calculates the gain value based on the lighting
735 conditions which can change over time.
739 Setting a new value for a volatile control will have no
740 effect and no ``V4L2_EVENT_CTRL_CH_VALUE`` will be sent, unless
741 the ``V4L2_CTRL_FLAG_EXECUTE_ON_WRITE`` flag (see below) is
742 also set. Otherwise the new value will just be ignored.
746 - ``V4L2_CTRL_FLAG_HAS_PAYLOAD``
750 - This control has a pointer type, so its value has to be accessed
751 using one of the pointer fields of struct
752 :ref:`v4l2_ext_control <v4l2-ext-control>`. This flag is set
753 for controls that are an array, string, or have a compound type.
754 In all cases you have to set a pointer to memory containing the
755 payload of the control.
759 - ``V4L2_CTRL_FLAG_EXECUTE_ON_WRITE``
763 - The value provided to the control will be propagated to the driver
764 even if it remains constant. This is required when the control
765 represents an action on the hardware. For example: clearing an
766 error flag or triggering the flash. All the controls of the type
767 ``V4L2_CTRL_TYPE_BUTTON`` have this flag set.
773 On success 0 is returned, on error -1 and the ``errno`` variable is set
774 appropriately. The generic error codes are described at the
775 :ref:`Generic Error Codes <gen-errors>` chapter.
778 The struct :ref:`v4l2_queryctrl <v4l2-queryctrl>` ``id`` is
779 invalid. The struct :ref:`v4l2_querymenu <v4l2-querymenu>` ``id``
780 is invalid or ``index`` is out of range (less than ``minimum`` or
781 greater than ``maximum``) or this particular menu item is not
782 supported by the driver.
785 An attempt was made to read a write-only control.
788 ``V4L2_CTRL_FLAG_DISABLED`` was intended for two purposes: Drivers
789 can skip predefined controls not supported by the hardware (although
790 returning ``EINVAL`` would do as well), or disable predefined and private
791 controls after hardware detection without the trouble of reordering
792 control arrays and indices (``EINVAL`` cannot be used to skip private
793 controls because it would prematurely end the enumeration).
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