1 .. -*- coding: utf-8; mode: rst -*-
5 *******************************************************************
6 ioctls VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL and VIDIOC_QUERYMENU
7 *******************************************************************
9 *man VIDIOC_QUERYCTRL(2)*
13 Enumerate controls and menu control items
19 .. cpp:function:: int ioctl( int fd, int request, struct v4l2_queryctrl *argp )
21 .. cpp:function:: int ioctl( int fd, int request, struct v4l2_query_ext_ctrl *argp )
23 .. 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. [1]_
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``,
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.
90 See also the examples in :ref:`control`.
95 .. flat-table:: struct v4l2_queryctrl
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.
119 - Type of control, see :ref:`v4l2-ctrl-type`.
127 - Name of the control, a NUL-terminated ASCII string. This
128 information is intended for the user.
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.
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.
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.
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.
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.
176 Note that although signed, the step value is supposed to be always
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
197 - Control flags, see :ref:`control-flags`.
205 - Reserved for future extensions. Drivers must set the array to
210 .. _v4l2-query-ext-ctrl:
212 .. flat-table:: struct v4l2_query_ext_ctrl
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
239 - Type of control, see :ref:`v4l2-ctrl-type`.
247 - Name of the control, a NUL-terminated ASCII string. This
248 information is intended for the user.
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.
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.
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.
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.
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.
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.
314 - Control flags, see :ref:`control-flags`.
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
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
346 - The number of dimension in the N-dimensional array. If this
347 control is not an array, then this field is 0.
353 - ``dims[V4L2_CTRL_MAX_DIMS]``
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.
364 - Reserved for future extensions. Applications and drivers must set
371 .. flat-table:: struct v4l2_querymenu
384 - Identifies the control, set by the application from the respective
385 struct :ref:`v4l2_queryctrl <v4l2-queryctrl>` ``id``.
394 - Index of the menu item, starting at zero, set by the application.
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.
422 - Value of the integer menu item. This field is valid for
423 ``V4L2_CTRL_FLAG_INTEGER_MENU`` type controls.
432 - Reserved for future extensions. Drivers must set the array to
439 .. flat-table:: enum v4l2_ctrl_type
459 - ``V4L2_CTRL_TYPE_INTEGER``
467 - An integer-valued control ranging from minimum to maximum
468 inclusive. The step value indicates the increment between values.
472 - ``V4L2_CTRL_TYPE_BOOLEAN``
480 - A boolean-valued control. Zero corresponds to "disabled", and one
485 - ``V4L2_CTRL_TYPE_MENU``
493 - The control has a menu of N choices. The names of the menu items
494 can be enumerated with the ``VIDIOC_QUERYMENU`` ioctl.
498 - ``V4L2_CTRL_TYPE_INTEGER_MENU``
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.
513 - ``V4L2_CTRL_TYPE_BITMASK``
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.
527 - ``V4L2_CTRL_TYPE_BUTTON``
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.
541 - ``V4L2_CTRL_TYPE_INTEGER64``
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``.
557 - ``V4L2_CTRL_TYPE_STRING``
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
569 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` you need to
570 set the ``size`` field of struct
571 :ref:`v4l2_ext_control <v4l2-ext-control>` to 9. For
572 :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` you can set
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.
579 - ``V4L2_CTRL_TYPE_CTRL_CLASS``
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.
595 - ``V4L2_CTRL_TYPE_U8``
603 - An unsigned 8-bit valued control ranging from minimum to maximum
604 inclusive. The step value indicates the increment between values.
608 - ``V4L2_CTRL_TYPE_U16``
616 - An unsigned 16-bit valued control ranging from minimum to maximum
617 inclusive. The step value indicates the increment between values.
621 - ``V4L2_CTRL_TYPE_U32``
629 - An unsigned 32-bit valued control ranging from minimum to maximum
630 inclusive. The step value indicates the increment between values.
636 .. flat-table:: Control Flags
644 - ``V4L2_CTRL_FLAG_DISABLED``
648 - This control is permanently disabled and should be ignored by the
649 application. Any attempt to change the control will result in an
654 - ``V4L2_CTRL_FLAG_GRABBED``
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.
665 - ``V4L2_CTRL_FLAG_READ_ONLY``
669 - This control is permanently readable only. Any attempt to change
670 the control will result in an EINVAL error code.
674 - ``V4L2_CTRL_FLAG_UPDATE``
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.
684 - ``V4L2_CTRL_FLAG_INACTIVE``
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.
695 - ``V4L2_CTRL_FLAG_SLIDER``
699 - A hint that this control is best represented as a slider-like
700 element in a user interface.
704 - ``V4L2_CTRL_FLAG_WRITE_ONLY``
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
717 - ``V4L2_CTRL_FLAG_VOLATILE``
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.
733 - ``V4L2_CTRL_FLAG_HAS_PAYLOAD``
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.
746 - ``V4L2_CTRL_FLAG_EXECUTE_ON_WRITE``
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.
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.
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.
773 An attempt was made to read a write-only control.
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).
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:
789 .. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook
790 .. ------------------------------------------------------------------------------