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+.. -*- coding: utf-8; mode: rst -*-
+
+.. _VIDIOC_QUERYCTRL:
+
+*******************************************************************
+ioctls VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL and VIDIOC_QUERYMENU
+*******************************************************************
+
+Name
+====
+
+VIDIOC_QUERYCTRL - VIDIOC_QUERY_EXT_CTRL - VIDIOC_QUERYMENU - Enumerate controls and menu control items
+
+
+Synopsis
+========
+
+.. cpp:function:: int ioctl( int fd, int request, struct v4l2_queryctrl *argp )
+
+.. cpp:function:: int ioctl( int fd, int request, struct v4l2_query_ext_ctrl *argp )
+
+.. cpp:function:: int ioctl( int fd, int request, struct v4l2_querymenu *argp )
+
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by :ref:`open() <func-open>`.
+
+``request``
+    VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL, VIDIOC_QUERYMENU
+
+``argp``
+
+
+Description
+===========
+
+To query the attributes of a control applications set the ``id`` field
+of a struct :ref:`v4l2_queryctrl <v4l2-queryctrl>` and call the
+``VIDIOC_QUERYCTRL`` ioctl with a pointer to this structure. The driver
+fills the rest of the structure or returns an ``EINVAL`` error code when the
+``id`` is invalid.
+
+It is possible to enumerate controls by calling ``VIDIOC_QUERYCTRL``
+with successive ``id`` values starting from ``V4L2_CID_BASE`` up to and
+exclusive ``V4L2_CID_LASTP1``. Drivers may return ``EINVAL`` if a control in
+this range is not supported. Further applications can enumerate private
+controls, which are not defined in this specification, by starting at
+``V4L2_CID_PRIVATE_BASE`` and incrementing ``id`` until the driver
+returns ``EINVAL``.
+
+In both cases, when the driver sets the ``V4L2_CTRL_FLAG_DISABLED`` flag
+in the ``flags`` field this control is permanently disabled and should
+be ignored by the application. [#f1]_
+
+When the application ORs ``id`` with ``V4L2_CTRL_FLAG_NEXT_CTRL`` the
+driver returns the next supported non-compound control, or ``EINVAL`` if
+there is none. In addition, the ``V4L2_CTRL_FLAG_NEXT_COMPOUND`` flag
+can be specified to enumerate all compound controls (i.e. controls with
+type ≥ ``V4L2_CTRL_COMPOUND_TYPES`` and/or array control, in other words
+controls that contain more than one value). Specify both
+``V4L2_CTRL_FLAG_NEXT_CTRL`` and ``V4L2_CTRL_FLAG_NEXT_COMPOUND`` in
+order to enumerate all controls, compound or not. Drivers which do not
+support these flags yet always return ``EINVAL``.
+
+The ``VIDIOC_QUERY_EXT_CTRL`` ioctl was introduced in order to better
+support controls that can use compound types, and to expose additional
+control information that cannot be returned in struct
+:ref:`v4l2_queryctrl <v4l2-queryctrl>` since that structure is full.
+
+``VIDIOC_QUERY_EXT_CTRL`` is used in the same way as
+``VIDIOC_QUERYCTRL``, except that the ``reserved`` array must be zeroed
+as well.
+
+Additional information is required for menu controls: the names of the
+menu items. To query them applications set the ``id`` and ``index``
+fields of struct :ref:`v4l2_querymenu <v4l2-querymenu>` and call the
+``VIDIOC_QUERYMENU`` ioctl with a pointer to this structure. The driver
+fills the rest of the structure or returns an ``EINVAL`` error code when the
+``id`` or ``index`` is invalid. Menu items are enumerated by calling
+``VIDIOC_QUERYMENU`` with successive ``index`` values from struct
+:ref:`v4l2_queryctrl <v4l2-queryctrl>` ``minimum`` to ``maximum``,
+inclusive.
+
+.. note:: It is possible for ``VIDIOC_QUERYMENU`` to return
+   an ``EINVAL`` error code for some indices between ``minimum`` and
+   ``maximum``. In that case that particular menu item is not supported by
+   this driver. Also note that the ``minimum`` value is not necessarily 0.
+
+See also the examples in :ref:`control`.
+
+
+.. _v4l2-queryctrl:
+
+.. flat-table:: struct v4l2_queryctrl
+    :header-rows:  0
+    :stub-columns: 0
+    :widths:       1 1 2
+
+
+    -  .. row 1
+
+       -  __u32
+
+       -  ``id``
+
+       -  Identifies the control, set by the application. See
+	  :ref:`control-id` for predefined IDs. When the ID is ORed with
+	  V4L2_CTRL_FLAG_NEXT_CTRL the driver clears the flag and
+	  returns the first control with a higher ID. Drivers which do not
+	  support this flag yet always return an ``EINVAL`` error code.
+
+    -  .. row 2
+
+       -  __u32
+
+       -  ``type``
+
+       -  Type of control, see :ref:`v4l2-ctrl-type`.
+
+    -  .. row 3
+
+       -  __u8
+
+       -  ``name``\ [32]
+
+       -  Name of the control, a NUL-terminated ASCII string. This
+	  information is intended for the user.
+
+    -  .. row 4
+
+       -  __s32
+
+       -  ``minimum``
+
+       -  Minimum value, inclusive. This field gives a lower bound for the
+	  control. See enum :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how
+	  the minimum value is to be used for each possible control type.
+	  Note that this a signed 32-bit value.
+
+    -  .. row 5
+
+       -  __s32
+
+       -  ``maximum``
+
+       -  Maximum value, inclusive. This field gives an upper bound for the
+	  control. See enum :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how
+	  the maximum value is to be used for each possible control type.
+	  Note that this a signed 32-bit value.
+
+    -  .. row 6
+
+       -  __s32
+
+       -  ``step``
+
+       -  This field gives a step size for the control. See enum
+	  :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how the step value is
+	  to be used for each possible control type. Note that this an
+	  unsigned 32-bit value.
+
+	  Generally drivers should not scale hardware control values. It may
+	  be necessary for example when the ``name`` or ``id`` imply a
+	  particular unit and the hardware actually accepts only multiples
+	  of said unit. If so, drivers must take care values are properly
+	  rounded when scaling, such that errors will not accumulate on
+	  repeated read-write cycles.
+
+	  This field gives the smallest change of an integer control
+	  actually affecting hardware. Often the information is needed when
+	  the user can change controls by keyboard or GUI buttons, rather
+	  than a slider. When for example a hardware register accepts values
+	  0-511 and the driver reports 0-65535, step should be 128.
+
+	  Note that although signed, the step value is supposed to be always
+	  positive.
+
+    -  .. row 7
+
+       -  __s32
+
+       -  ``default_value``
+
+       -  The default value of a ``V4L2_CTRL_TYPE_INTEGER``, ``_BOOLEAN``,
+	  ``_BITMASK``, ``_MENU`` or ``_INTEGER_MENU`` control. Not valid
+	  for other types of controls.
+
+	  .. note:: Drivers reset controls to their default value only when
+	     the driver is first loaded, never afterwards.
+
+    -  .. row 8
+
+       -  __u32
+
+       -  ``flags``
+
+       -  Control flags, see :ref:`control-flags`.
+
+    -  .. row 9
+
+       -  __u32
+
+       -  ``reserved``\ [2]
+
+       -  Reserved for future extensions. Drivers must set the array to
+	  zero.
+
+
+
+.. _v4l2-query-ext-ctrl:
+
+.. flat-table:: struct v4l2_query_ext_ctrl
+    :header-rows:  0
+    :stub-columns: 0
+    :widths:       1 1 2
+
+
+    -  .. row 1
+
+       -  __u32
+
+       -  ``id``
+
+       -  Identifies the control, set by the application. See
+	  :ref:`control-id` for predefined IDs. When the ID is ORed with
+	  ``V4L2_CTRL_FLAG_NEXT_CTRL`` the driver clears the flag and
+	  returns the first non-compound control with a higher ID. When the
+	  ID is ORed with ``V4L2_CTRL_FLAG_NEXT_COMPOUND`` the driver clears
+	  the flag and returns the first compound control with a higher ID.
+	  Set both to get the first control (compound or not) with a higher
+	  ID.
+
+    -  .. row 2
+
+       -  __u32
+
+       -  ``type``
+
+       -  Type of control, see :ref:`v4l2-ctrl-type`.
+
+    -  .. row 3
+
+       -  char
+
+       -  ``name``\ [32]
+
+       -  Name of the control, a NUL-terminated ASCII string. This
+	  information is intended for the user.
+
+    -  .. row 4
+
+       -  __s64
+
+       -  ``minimum``
+
+       -  Minimum value, inclusive. This field gives a lower bound for the
+	  control. See enum :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how
+	  the minimum value is to be used for each possible control type.
+	  Note that this a signed 64-bit value.
+
+    -  .. row 5
+
+       -  __s64
+
+       -  ``maximum``
+
+       -  Maximum value, inclusive. This field gives an upper bound for the
+	  control. See enum :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how
+	  the maximum value is to be used for each possible control type.
+	  Note that this a signed 64-bit value.
+
+    -  .. row 6
+
+       -  __u64
+
+       -  ``step``
+
+       -  This field gives a step size for the control. See enum
+	  :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how the step value is
+	  to be used for each possible control type. Note that this an
+	  unsigned 64-bit value.
+
+	  Generally drivers should not scale hardware control values. It may
+	  be necessary for example when the ``name`` or ``id`` imply a
+	  particular unit and the hardware actually accepts only multiples
+	  of said unit. If so, drivers must take care values are properly
+	  rounded when scaling, such that errors will not accumulate on
+	  repeated read-write cycles.
+
+	  This field gives the smallest change of an integer control
+	  actually affecting hardware. Often the information is needed when
+	  the user can change controls by keyboard or GUI buttons, rather
+	  than a slider. When for example a hardware register accepts values
+	  0-511 and the driver reports 0-65535, step should be 128.
+
+    -  .. row 7
+
+       -  __s64
+
+       -  ``default_value``
+
+       -  The default value of a ``V4L2_CTRL_TYPE_INTEGER``, ``_INTEGER64``,
+	  ``_BOOLEAN``, ``_BITMASK``, ``_MENU``, ``_INTEGER_MENU``, ``_U8``
+	  or ``_U16`` control. Not valid for other types of controls.
+
+	  .. note:: Drivers reset controls to their default value only when
+	     the driver is first loaded, never afterwards.
+
+    -  .. row 8
+
+       -  __u32
+
+       -  ``flags``
+
+       -  Control flags, see :ref:`control-flags`.
+
+    -  .. row 9
+
+       -  __u32
+
+       -  ``elem_size``
+
+       -  The size in bytes of a single element of the array. Given a char
+	  pointer ``p`` to a 3-dimensional array you can find the position
+	  of cell ``(z, y, x)`` as follows:
+	  ``p + ((z * dims[1] + y) * dims[0] + x) * elem_size``.
+	  ``elem_size`` is always valid, also when the control isn't an
+	  array. For string controls ``elem_size`` is equal to
+	  ``maximum + 1``.
+
+    -  .. row 10
+
+       -  __u32
+
+       -  ``elems``
+
+       -  The number of elements in the N-dimensional array. If this control
+	  is not an array, then ``elems`` is 1. The ``elems`` field can
+	  never be 0.
+
+    -  .. row 11
+
+       -  __u32
+
+       -  ``nr_of_dims``
+
+       -  The number of dimension in the N-dimensional array. If this
+	  control is not an array, then this field is 0.
+
+    -  .. row 12
+
+       -  __u32
+
+       -  ``dims[V4L2_CTRL_MAX_DIMS]``
+
+       -  The size of each dimension. The first ``nr_of_dims`` elements of
+	  this array must be non-zero, all remaining elements must be zero.
+
+    -  .. row 13
+
+       -  __u32
+
+       -  ``reserved``\ [32]
+
+       -  Reserved for future extensions. Applications and drivers must set
+	  the array to zero.
+
+
+
+.. _v4l2-querymenu:
+
+.. flat-table:: struct v4l2_querymenu
+    :header-rows:  0
+    :stub-columns: 0
+    :widths:       1 1 2 1
+
+
+    -  .. row 1
+
+       -  __u32
+
+       -
+       -  ``id``
+
+       -  Identifies the control, set by the application from the respective
+	  struct :ref:`v4l2_queryctrl <v4l2-queryctrl>` ``id``.
+
+    -  .. row 2
+
+       -  __u32
+
+       -
+       -  ``index``
+
+       -  Index of the menu item, starting at zero, set by the application.
+
+    -  .. row 3
+
+       -  union
+
+       -
+       -
+       -
+
+    -  .. row 4
+
+       -
+       -  __u8
+
+       -  ``name``\ [32]
+
+       -  Name of the menu item, a NUL-terminated ASCII string. This
+	  information is intended for the user. This field is valid for
+	  ``V4L2_CTRL_FLAG_MENU`` type controls.
+
+    -  .. row 5
+
+       -
+       -  __s64
+
+       -  ``value``
+
+       -  Value of the integer menu item. This field is valid for
+	  ``V4L2_CTRL_FLAG_INTEGER_MENU`` type controls.
+
+    -  .. row 6
+
+       -  __u32
+
+       -
+       -  ``reserved``
+
+       -  Reserved for future extensions. Drivers must set the array to
+	  zero.
+
+
+
+.. _v4l2-ctrl-type:
+
+.. flat-table:: enum v4l2_ctrl_type
+    :header-rows:  1
+    :stub-columns: 0
+    :widths:       30 5 5 5 55
+
+
+    -  .. row 1
+
+       -  Type
+
+       -  ``minimum``
+
+       -  ``step``
+
+       -  ``maximum``
+
+       -  Description
+
+    -  .. row 2
+
+       -  ``V4L2_CTRL_TYPE_INTEGER``
+
+       -  any
+
+       -  any
+
+       -  any
+
+       -  An integer-valued control ranging from minimum to maximum
+	  inclusive. The step value indicates the increment between values.
+
+    -  .. row 3
+
+       -  ``V4L2_CTRL_TYPE_BOOLEAN``
+
+       -  0
+
+       -  1
+
+       -  1
+
+       -  A boolean-valued control. Zero corresponds to "disabled", and one
+	  means "enabled".
+
+    -  .. row 4
+
+       -  ``V4L2_CTRL_TYPE_MENU``
+
+       -  ≥ 0
+
+       -  1
+
+       -  N-1
+
+       -  The control has a menu of N choices. The names of the menu items
+	  can be enumerated with the ``VIDIOC_QUERYMENU`` ioctl.
+
+    -  .. row 5
+
+       -  ``V4L2_CTRL_TYPE_INTEGER_MENU``
+
+       -  ≥ 0
+
+       -  1
+
+       -  N-1
+
+       -  The control has a menu of N choices. The values of the menu items
+	  can be enumerated with the ``VIDIOC_QUERYMENU`` ioctl. This is
+	  similar to ``V4L2_CTRL_TYPE_MENU`` except that instead of strings,
+	  the menu items are signed 64-bit integers.
+
+    -  .. row 6
+
+       -  ``V4L2_CTRL_TYPE_BITMASK``
+
+       -  0
+
+       -  n/a
+
+       -  any
+
+       -  A bitmask field. The maximum value is the set of bits that can be
+	  used, all other bits are to be 0. The maximum value is interpreted
+	  as a __u32, allowing the use of bit 31 in the bitmask.
+
+    -  .. row 7
+
+       -  ``V4L2_CTRL_TYPE_BUTTON``
+
+       -  0
+
+       -  0
+
+       -  0
+
+       -  A control which performs an action when set. Drivers must ignore
+	  the value passed with ``VIDIOC_S_CTRL`` and return an ``EINVAL`` error
+	  code on a ``VIDIOC_G_CTRL`` attempt.
+
+    -  .. row 8
+
+       -  ``V4L2_CTRL_TYPE_INTEGER64``
+
+       -  any
+
+       -  any
+
+       -  any
+
+       -  A 64-bit integer valued control. Minimum, maximum and step size
+	  cannot be queried using ``VIDIOC_QUERYCTRL``. Only
+	  ``VIDIOC_QUERY_EXT_CTRL`` can retrieve the 64-bit min/max/step
+	  values, they should be interpreted as n/a when using
+	  ``VIDIOC_QUERYCTRL``.
+
+    -  .. row 9
+
+       -  ``V4L2_CTRL_TYPE_STRING``
+
+       -  ≥ 0
+
+       -  ≥ 1
+
+       -  ≥ 0
+
+       -  The minimum and maximum string lengths. The step size means that
+	  the string must be (minimum + N * step) characters long for N ≥ 0.
+	  These lengths do not include the terminating zero, so in order to
+	  pass a string of length 8 to
+	  :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` you need to
+	  set the ``size`` field of struct
+	  :ref:`v4l2_ext_control <v4l2-ext-control>` to 9. For
+	  :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` you can set
+	  the ``size`` field to ``maximum`` + 1. Which character encoding is
+	  used will depend on the string control itself and should be part
+	  of the control documentation.
+
+    -  .. row 10
+
+       -  ``V4L2_CTRL_TYPE_CTRL_CLASS``
+
+       -  n/a
+
+       -  n/a
+
+       -  n/a
+
+       -  This is not a control. When ``VIDIOC_QUERYCTRL`` is called with a
+	  control ID equal to a control class code (see :ref:`ctrl-class`)
+	  + 1, the ioctl returns the name of the control class and this
+	  control type. Older drivers which do not support this feature
+	  return an ``EINVAL`` error code.
+
+    -  .. row 11
+
+       -  ``V4L2_CTRL_TYPE_U8``
+
+       -  any
+
+       -  any
+
+       -  any
+
+       -  An unsigned 8-bit valued control ranging from minimum to maximum
+	  inclusive. The step value indicates the increment between values.
+
+    -  .. row 12
+
+       -  ``V4L2_CTRL_TYPE_U16``
+
+       -  any
+
+       -  any
+
+       -  any
+
+       -  An unsigned 16-bit valued control ranging from minimum to maximum
+	  inclusive. The step value indicates the increment between values.
+
+    -  .. row 13
+
+       -  ``V4L2_CTRL_TYPE_U32``
+
+       -  any
+
+       -  any
+
+       -  any
+
+       -  An unsigned 32-bit valued control ranging from minimum to maximum
+	  inclusive. The step value indicates the increment between values.
+
+
+
+.. _control-flags:
+
+.. flat-table:: Control Flags
+    :header-rows:  0
+    :stub-columns: 0
+    :widths:       3 1 4
+
+
+    -  .. row 1
+
+       -  ``V4L2_CTRL_FLAG_DISABLED``
+
+       -  0x0001
+
+       -  This control is permanently disabled and should be ignored by the
+	  application. Any attempt to change the control will result in an
+	  ``EINVAL`` error code.
+
+    -  .. row 2
+
+       -  ``V4L2_CTRL_FLAG_GRABBED``
+
+       -  0x0002
+
+       -  This control is temporarily unchangeable, for example because
+	  another application took over control of the respective resource.
+	  Such controls may be displayed specially in a user interface.
+	  Attempts to change the control may result in an ``EBUSY`` error code.
+
+    -  .. row 3
+
+       -  ``V4L2_CTRL_FLAG_READ_ONLY``
+
+       -  0x0004
+
+       -  This control is permanently readable only. Any attempt to change
+	  the control will result in an ``EINVAL`` error code.
+
+    -  .. row 4
+
+       -  ``V4L2_CTRL_FLAG_UPDATE``
+
+       -  0x0008
+
+       -  A hint that changing this control may affect the value of other
+	  controls within the same control class. Applications should update
+	  their user interface accordingly.
+
+    -  .. row 5
+
+       -  ``V4L2_CTRL_FLAG_INACTIVE``
+
+       -  0x0010
+
+       -  This control is not applicable to the current configuration and
+	  should be displayed accordingly in a user interface. For example
+	  the flag may be set on a MPEG audio level 2 bitrate control when
+	  MPEG audio encoding level 1 was selected with another control.
+
+    -  .. row 6
+
+       -  ``V4L2_CTRL_FLAG_SLIDER``
+
+       -  0x0020
+
+       -  A hint that this control is best represented as a slider-like
+	  element in a user interface.
+
+    -  .. row 7
+
+       -  ``V4L2_CTRL_FLAG_WRITE_ONLY``
+
+       -  0x0040
+
+       -  This control is permanently writable only. Any attempt to read the
+	  control will result in an ``EACCES`` error code error code. This flag
+	  is typically present for relative controls or action controls
+	  where writing a value will cause the device to carry out a given
+	  action (e. g. motor control) but no meaningful value can be
+	  returned.
+
+    -  .. row 8
+
+       -  ``V4L2_CTRL_FLAG_VOLATILE``
+
+       -  0x0080
+
+       -  This control is volatile, which means that the value of the
+	  control changes continuously. A typical example would be the
+	  current gain value if the device is in auto-gain mode. In such a
+	  case the hardware calculates the gain value based on the lighting
+	  conditions which can change over time.
+
+	  .. note:: Setting a new value for a volatile control will have no
+	     effect and no ``V4L2_EVENT_CTRL_CH_VALUE`` will be sent, unless
+	     the ``V4L2_CTRL_FLAG_EXECUTE_ON_WRITE`` flag (see below) is
+	     also set. Otherwise the new value will just be ignored.
+
+    -  .. row 9
+
+       -  ``V4L2_CTRL_FLAG_HAS_PAYLOAD``
+
+       -  0x0100
+
+       -  This control has a pointer type, so its value has to be accessed
+	  using one of the pointer fields of struct
+	  :ref:`v4l2_ext_control <v4l2-ext-control>`. This flag is set
+	  for controls that are an array, string, or have a compound type.
+	  In all cases you have to set a pointer to memory containing the
+	  payload of the control.
+
+    -  .. row 10
+
+       -  ``V4L2_CTRL_FLAG_EXECUTE_ON_WRITE``
+
+       -  0x0200
+
+       -  The value provided to the control will be propagated to the driver
+	  even if it remains constant. This is required when the control
+	  represents an action on the hardware. For example: clearing an
+	  error flag or triggering the flash. All the controls of the type
+	  ``V4L2_CTRL_TYPE_BUTTON`` have this flag set.
+
+
+Return Value
+============
+
+On success 0 is returned, on error -1 and the ``errno`` variable is set
+appropriately. The generic error codes are described at the
+:ref:`Generic Error Codes <gen-errors>` chapter.
+
+EINVAL
+    The struct :ref:`v4l2_queryctrl <v4l2-queryctrl>` ``id`` is
+    invalid. The struct :ref:`v4l2_querymenu <v4l2-querymenu>` ``id``
+    is invalid or ``index`` is out of range (less than ``minimum`` or
+    greater than ``maximum``) or this particular menu item is not
+    supported by the driver.
+
+EACCES
+    An attempt was made to read a write-only control.
+
+.. [#f1]
+   ``V4L2_CTRL_FLAG_DISABLED`` was intended for two purposes: Drivers
+   can skip predefined controls not supported by the hardware (although
+   returning ``EINVAL`` would do as well), or disable predefined and private
+   controls after hardware detection without the trouble of reordering
+   control arrays and indices (``EINVAL`` cannot be used to skip private
+   controls because it would prematurely end the enumeration).