| .. -*- coding: utf-8; mode: rst -*- |
| |
| .. _vidioc-queryctrl: |
| |
| *************************************************************** |
| ioctl VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL, VIDIOC_QUERYMENU |
| *************************************************************** |
| |
| *man VIDIOC_QUERYCTRL(2)* |
| |
| VIDIOC_QUERY_EXT_CTRL |
| VIDIOC_QUERYMENU |
| Enumerate controls and menu control items |
| |
| |
| Synopsis |
| ======== |
| |
| .. c:function:: int ioctl( int fd, int request, struct v4l2_queryctrl *argp ) |
| |
| .. c:function:: int ioctl( int fd, int request, struct v4l2_query_ext_ctrl *argp ) |
| |
| .. c: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. [1]_ |
| |
| 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 that 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 that 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 |
| that 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 that 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. |
| |
| .. [1] |
| ``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). |
| |
| |
| .. ------------------------------------------------------------------------------ |
| .. This file was automatically converted from DocBook-XML with the dbxml |
| .. library (https://github.com/return42/sphkerneldoc). The origin XML comes |
| .. from the linux kernel, refer to: |
| .. |
| .. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook |
| .. ------------------------------------------------------------------------------ |
