Documentation/media/uapi/v4l/vidioc-g-ext-ctrls.rst - LeafOS-Devices/android_kernel_samsung_gta4xl - Gitiles

 .. -*- 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.
	.. -- 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.