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+.. -*- coding: utf-8; mode: rst -*-
+
+.. _VIDIOC_G_EXT_CTRLS:
+
+******************************************************************
+ioctl VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS, VIDIOC_TRY_EXT_CTRLS
+******************************************************************
+
+Name
+====
+
+VIDIOC_G_EXT_CTRLS - VIDIOC_S_EXT_CTRLS - VIDIOC_TRY_EXT_CTRLS - Get or set the value of several controls, try control values
+
+
+Synopsis
+========
+
+.. cpp:function:: int ioctl( int fd, int request, struct v4l2_ext_controls *argp )
+
+
+Arguments
+=========
+
+``fd``
+ File descriptor returned by :ref:`open() <func-open>`.
+
+``request``
+ VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS,
+ VIDIOC_TRY_EXT_CTRLS
+
+``argp``
+
+
+Description
+===========
+
+These ioctls allow the caller to get or set multiple controls
+atomically. Control IDs are grouped into control classes (see
+:ref:`ctrl-class`) and all controls in the control array must belong
+to the same control class.
+
+Applications must always fill in the ``count``, ``which``, ``controls``
+and ``reserved`` fields of struct
+:ref:`v4l2_ext_controls <v4l2-ext-controls>`, and initialize the
+struct :ref:`v4l2_ext_control <v4l2-ext-control>` array pointed to
+by the ``controls`` fields.
+
+To get the current value of a set of controls applications initialize
+the ``id``, ``size`` and ``reserved2`` fields of each struct
+:ref:`v4l2_ext_control <v4l2-ext-control>` and call the
+:ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctl. String controls controls must also set the
+``string`` field. Controls of compound types
+(``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set) must set the ``ptr`` field.
+
+If the ``size`` is too small to receive the control result (only
+relevant for pointer-type controls like strings), then the driver will
+set ``size`` to a valid value and return an ``ENOSPC`` error code. You
+should re-allocate the memory to this new size and try again. For the
+string type it is possible that the same issue occurs again if the
+string has grown in the meantime. It is recommended to call
+:ref:`VIDIOC_QUERYCTRL` first and use
+``maximum``\ +1 as the new ``size`` value. It is guaranteed that that is
+sufficient memory.
+
+N-dimensional arrays are set and retrieved row-by-row. You cannot set a
+partial array, all elements have to be set or retrieved. The total size
+is calculated as ``elems`` * ``elem_size``. These values can be obtained
+by calling :ref:`VIDIOC_QUERY_EXT_CTRL <VIDIOC_QUERYCTRL>`.
+
+To change the value of a set of controls applications initialize the
+``id``, ``size``, ``reserved2`` and ``value/value64/string/ptr`` fields
+of each struct :ref:`v4l2_ext_control <v4l2-ext-control>` and call
+the :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctl. The controls will only be set if *all*
+control values are valid.
+
+To check if a set of controls have correct values applications
+initialize the ``id``, ``size``, ``reserved2`` and
+``value/value64/string/ptr`` fields of each struct
+:ref:`v4l2_ext_control <v4l2-ext-control>` and call the
+:ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctl. It is up to the driver whether wrong
+values are automatically adjusted to a valid value or if an error is
+returned.
+
+When the ``id`` or ``which`` is invalid drivers return an ``EINVAL`` error
+code. When the value is out of bounds drivers can choose to take the
+closest valid value or return an ``ERANGE`` error code, whatever seems more
+appropriate. In the first case the new value is set in struct
+:ref:`v4l2_ext_control <v4l2-ext-control>`. If the new control value
+is inappropriate (e.g. the given menu index is not supported by the menu
+control), then this will also result in an ``EINVAL`` error code error.
+
+The driver will only set/get these controls if all control values are
+correct. This prevents the situation where only some of the controls
+were set/get. Only low-level errors (e. g. a failed i2c command) can
+still cause this situation.
+
+
+.. _v4l2-ext-control:
+
+.. flat-table:: struct v4l2_ext_control
+ :header-rows: 0
+ :stub-columns: 0
+ :widths: 1 1 1 2
+
+
+ - .. row 1
+
+ - __u32
+
+ - ``id``
+
+ -
+ - Identifies the control, set by the application.
+
+ - .. row 2
+
+ - __u32
+
+ - ``size``
+
+ -
+ - The total size in bytes of the payload of this control. This is
+ normally 0, but for pointer controls this should be set to the
+ size of the memory containing the payload, or that will receive
+ the payload. If :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` finds that this value is
+ less than is required to store the payload result, then it is set
+ to a value large enough to store the payload result and ``ENOSPC`` is
+ returned.
+
+ .. note:: For string controls, this ``size`` field should
+ not be confused with the length of the string. This field refers
+ to the size of the memory that contains the string. The actual
+ *length* of the string may well be much smaller.
+
+ - .. row 3
+
+ - __u32
+
+ - ``reserved2``\ [1]
+
+ -
+ - Reserved for future extensions. Drivers and applications must set
+ the array to zero.
+
+ - .. row 4
+
+ - union
+
+ - (anonymous)
+
+ - .. row 5
+
+ -
+ - __s32
+
+ - ``value``
+
+ - New value or current value. Valid if this control is not of type
+ ``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is
+ not set.
+
+ - .. row 6
+
+ -
+ - __s64
+
+ - ``value64``
+
+ - New value or current value. Valid if this control is of type
+ ``V4L2_CTRL_TYPE_INTEGER64`` and ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is
+ not set.
+
+ - .. row 7
+
+ -
+ - char *
+
+ - ``string``
+
+ - A pointer to a string. Valid if this control is of type
+ ``V4L2_CTRL_TYPE_STRING``.
+
+ - .. row 8
+
+ -
+ - __u8 *
+
+ - ``p_u8``
+
+ - A pointer to a matrix control of unsigned 8-bit values. Valid if
+ this control is of type ``V4L2_CTRL_TYPE_U8``.
+
+ - .. row 9
+
+ -
+ - __u16 *
+
+ - ``p_u16``
+
+ - A pointer to a matrix control of unsigned 16-bit values. Valid if
+ this control is of type ``V4L2_CTRL_TYPE_U16``.
+
+ - .. row 10
+
+ -
+ - __u32 *
+
+ - ``p_u32``
+
+ - A pointer to a matrix control of unsigned 32-bit values. Valid if
+ this control is of type ``V4L2_CTRL_TYPE_U32``.
+
+ - .. row 11
+
+ -
+ - void *
+
+ - ``ptr``
+
+ - A pointer to a compound type which can be an N-dimensional array
+ and/or a compound type (the control's type is >=
+ ``V4L2_CTRL_COMPOUND_TYPES``). Valid if
+ ``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set for this control.
+
+
+
+.. _v4l2-ext-controls:
+
+.. flat-table:: struct v4l2_ext_controls
+ :header-rows: 0
+ :stub-columns: 0
+ :widths: 1 1 2 1
+
+
+ - .. row 1
+
+ - union
+
+ - (anonymous)
+
+ - .. row 2
+
+ -
+ - __u32
+
+ - ``ctrl_class``
+
+ - The control class to which all controls belong, see
+ :ref:`ctrl-class`. Drivers that use a kernel framework for
+ handling controls will also accept a value of 0 here, meaning that
+ the controls can belong to any control class. Whether drivers
+ support this can be tested by setting ``ctrl_class`` to 0 and
+ calling :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` with a ``count`` of 0. If that
+ succeeds, then the driver supports this feature.
+
+ - .. row 3
+
+ -
+ - __u32
+
+ - ``which``
+
+ - Which value of the control to get/set/try.
+ ``V4L2_CTRL_WHICH_CUR_VAL`` will return the current value of the
+ control and ``V4L2_CTRL_WHICH_DEF_VAL`` will return the default
+ value of the control.
+
+ .. note:: You can only get the default value of the control,
+ you cannot set or try it.
+
+ For backwards compatibility you can also use a control class here
+ (see :ref:`ctrl-class`). In that case all controls have to
+ belong to that control class. This usage is deprecated, instead
+ just use ``V4L2_CTRL_WHICH_CUR_VAL``. There are some very old
+ drivers that do not yet support ``V4L2_CTRL_WHICH_CUR_VAL`` and
+ that require a control class here. You can test for such drivers
+ by setting ctrl_class to ``V4L2_CTRL_WHICH_CUR_VAL`` and calling
+ VIDIOC_TRY_EXT_CTRLS with a count of 0. If that fails, then the
+ driver does not support ``V4L2_CTRL_WHICH_CUR_VAL``.
+
+ - .. row 4
+
+ - __u32
+
+ - ``count``
+
+ - The number of controls in the controls array. May also be zero.
+
+ - .. row 5
+
+ - __u32
+
+ - ``error_idx``
+
+ - Set by the driver in case of an error. If the error is associated
+ with a particular control, then ``error_idx`` is set to the index
+ of that control. If the error is not related to a specific
+ control, or the validation step failed (see below), then
+ ``error_idx`` is set to ``count``. The value is undefined if the
+ ioctl returned 0 (success).
+
+ Before controls are read from/written to hardware a validation
+ step takes place: this checks if all controls in the list are
+ valid controls, if no attempt is made to write to a read-only
+ control or read from a write-only control, and any other up-front
+ checks that can be done without accessing the hardware. The exact
+ validations done during this step are driver dependent since some
+ checks might require hardware access for some devices, thus making
+ it impossible to do those checks up-front. However, drivers should
+ make a best-effort to do as many up-front checks as possible.
+
+ This check is done to avoid leaving the hardware in an
+ inconsistent state due to easy-to-avoid problems. But it leads to
+ another problem: the application needs to know whether an error
+ came from the validation step (meaning that the hardware was not
+ touched) or from an error during the actual reading from/writing
+ to hardware.
+
+ The, in hindsight quite poor, solution for that is to set
+ ``error_idx`` to ``count`` if the validation failed. This has the
+ unfortunate side-effect that it is not possible to see which
+ control failed the validation. If the validation was successful
+ and the error happened while accessing the hardware, then
+ ``error_idx`` is less than ``count`` and only the controls up to
+ ``error_idx-1`` were read or written correctly, and the state of
+ the remaining controls is undefined.
+
+ Since :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` does not access hardware there is
+ also no need to handle the validation step in this special way, so
+ ``error_idx`` will just be set to the control that failed the
+ validation step instead of to ``count``. This means that if
+ :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` fails with ``error_idx`` set to ``count``,
+ then you can call :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` to try to discover the
+ actual control that failed the validation step. Unfortunately,
+ there is no ``TRY`` equivalent for :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`.
+
+ - .. row 6
+
+ - __u32
+
+ - ``reserved``\ [2]
+
+ - Reserved for future extensions. Drivers and applications must set
+ the array to zero.
+
+ - .. row 7
+
+ - struct :ref:`v4l2_ext_control <v4l2-ext-control>` *
+
+ - ``controls``
+
+ - Pointer to an array of ``count`` v4l2_ext_control structures.
+ Ignored if ``count`` equals zero.
+
+
+
+.. _ctrl-class:
+
+.. flat-table:: Control classes
+ :header-rows: 0
+ :stub-columns: 0
+ :widths: 3 1 4
+
+
+ - .. row 1
+
+ - ``V4L2_CTRL_CLASS_USER``
+
+ - 0x980000
+
+ - The class containing user controls. These controls are described
+ in :ref:`control`. All controls that can be set using the
+ :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` and
+ :ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` ioctl belong to this
+ class.
+
+ - .. row 2
+
+ - ``V4L2_CTRL_CLASS_MPEG``
+
+ - 0x990000
+
+ - The class containing MPEG compression controls. These controls are
+ described in :ref:`mpeg-controls`.
+
+ - .. row 3
+
+ - ``V4L2_CTRL_CLASS_CAMERA``
+
+ - 0x9a0000
+
+ - The class containing camera controls. These controls are described
+ in :ref:`camera-controls`.
+
+ - .. row 4
+
+ - ``V4L2_CTRL_CLASS_FM_TX``
+
+ - 0x9b0000
+
+ - The class containing FM Transmitter (FM TX) controls. These
+ controls are described in :ref:`fm-tx-controls`.
+
+ - .. row 5
+
+ - ``V4L2_CTRL_CLASS_FLASH``
+
+ - 0x9c0000
+
+ - The class containing flash device controls. These controls are
+ described in :ref:`flash-controls`.
+
+ - .. row 6
+
+ - ``V4L2_CTRL_CLASS_JPEG``
+
+ - 0x9d0000
+
+ - The class containing JPEG compression controls. These controls are
+ described in :ref:`jpeg-controls`.
+
+ - .. row 7
+
+ - ``V4L2_CTRL_CLASS_IMAGE_SOURCE``
+
+ - 0x9e0000
+
+ - The class containing image source controls. These controls are
+ described in :ref:`image-source-controls`.
+
+ - .. row 8
+
+ - ``V4L2_CTRL_CLASS_IMAGE_PROC``
+
+ - 0x9f0000
+
+ - The class containing image processing controls. These controls are
+ described in :ref:`image-process-controls`.
+
+ - .. row 9
+
+ - ``V4L2_CTRL_CLASS_FM_RX``
+
+ - 0xa10000
+
+ - The class containing FM Receiver (FM RX) controls. These controls
+ are described in :ref:`fm-rx-controls`.
+
+ - .. row 10
+
+ - ``V4L2_CTRL_CLASS_RF_TUNER``
+
+ - 0xa20000
+
+ - The class containing RF tuner controls. These controls are
+ described in :ref:`rf-tuner-controls`.
+
+
+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_ext_control <v4l2-ext-control>` ``id`` is
+ invalid, the struct :ref:`v4l2_ext_controls <v4l2-ext-controls>`
+ ``which`` is invalid, or the struct
+ :ref:`v4l2_ext_control <v4l2-ext-control>` ``value`` was
+ inappropriate (e.g. the given menu index is not supported by the
+ driver). This error code is also returned by the
+ :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` and :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctls if two or
+ more control values are in conflict.
+
+ERANGE
+ The struct :ref:`v4l2_ext_control <v4l2-ext-control>` ``value``
+ is out of bounds.
+
+EBUSY
+ The control is temporarily not changeable, possibly because another
+ applications took over control of the device function this control
+ belongs to.
+
+ENOSPC
+ The space reserved for the control's payload is insufficient. The
+ field ``size`` is set to a value that is enough to store the payload
+ and this error code is returned.
+
+EACCES
+ Attempt to try or set a read-only control or to get a write-only
+ control.