ioctl VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS, VIDIOC_TRY_EXT_CTRLS

&manvol;

VIDIOC_G_EXT_CTRLS

VIDIOC_S_EXT_CTRLS

VIDIOC_TRY_EXT_CTRLS

Get or set the value of several controls, try control values

    	int ioctl
    	int fd
    	int request
    	struct v4l2_ext_controls
    *argp

## Arguments

`fd`

- &fd;

`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 ctrl-class) and all controls in the control array must belong to the same control class.

Applications must always fill in the count, ctrl_class, controls and reserved fields of &v4l2-ext-controls;, and initialize the &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 &v4l2-ext-control; and call the `VIDIOC_G_EXT_CTRLS` ioctl. String controls controls must also set the string 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;. You should re-allocate the string memory to this new size and try again. It is possible that the same issue occurs again if the string has grown in the meantime. It is recommended to call &VIDIOC-QUERYCTRL; first and use maximum+1 as the new size value. It is guaranteed that that is sufficient memory.

To change the value of a set of controls applications initialize the id, size, reserved2 and value/string fields of each &v4l2-ext-control; and call the `VIDIOC_S_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/string fields of each &v4l2-ext-control; and call the `VIDIOC_TRY_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 ctrl_class is invalid drivers return an &EINVAL;. When the value is out of bounds drivers can choose to take the closest valid value or return an &ERANGE;, whatever seems more appropriate. In the first case the new value is set in &v4l2-ext-control;.

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 (⪚ a failed i2c command) can still cause this situation.

## struct v4l2_ext_control

&cs-ustr;
__u32 | id |  | Identifies the control, set by the application.
__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 `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 that 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.
__u32 | reserved2[1] |  | Reserved for future extensions. Drivers and applications must set the array to zero.
union | (anonymous)
| __s32 | value | New value or current value.
| __s64 | value64 | New value or current value.
| char * | string | A pointer to a string.

## struct v4l2_ext_controls

&cs-str;
__u32 | ctrl_class | The control class to which all controls belong, see ctrl-class.
__u32 | count | The number of controls in the controls array. May also be zero.
__u32 | error_idx | Set by the driver in case of an error. It is the index of the control causing the error or equal to 'count' when the error is not associated with a particular control. Undefined when the ioctl returns 0 (success).
__u32 | reserved[2] | Reserved for future extensions. Drivers and applications must set the array to zero.
&v4l2-ext-control; * | controls | Pointer to an array of count v4l2_ext_control structures. Ignored if count equals zero.

## Control classes

&cs-def;
`V4L2_CTRL_CLASS_USER` | 0x980000 | The class containing user controls. These controls are described in control. All controls that can be set using the &VIDIOC-S-CTRL; and &VIDIOC-G-CTRL; ioctl belong to this class.
`V4L2_CTRL_CLASS_MPEG` | 0x990000 | The class containing MPEG compression controls. These controls are described in mpeg-controls.
`V4L2_CTRL_CLASS_CAMERA` | 0x9a0000 | The class containing camera controls. These controls are described in camera-controls.
`V4L2_CTRL_CLASS_FM_TX` | 0x9b0000 | The class containing FM Transmitter (FM TX) controls. These controls are described in fm-tx-controls.

&return-value;

EINVAL

- The &v4l2-ext-control; id is invalid or the &v4l2-ext-controls; ctrl_class is invalid. This error code is also returned by the `VIDIOC_S_EXT_CTRLS` and `VIDIOC_TRY_EXT_CTRLS` ioctls if two or more control values are in conflict.

ERANGE

- The &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.