Video for Linux Two API Specification: Revision 0.24
Prev |  | Next

# 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

``int ioctl`(int fd, int request, struct v4l2_ext_controls *argp);`

## Arguments

`fd`

  File descriptor returned by `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 Table 3) 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 struct v4l2_ext_controls, and initialize the struct v4l2_ext_control array pointed to by the `controls` fields.

To get the current value of a set of controls applications initialize the `id` field of each struct v4l2_ext_control and call the `VIDIOC_G_EXT_CTRLS` ioctl.

To change the value of a set of controls applications initialize the `id` and `value` fields of a struct 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 the a set of controls have correct values applications initialize the `id` and `value` fields of a struct 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 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 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 (e. g. a failed i2c command) can still cause this situation.

Table 1. struct `v4l2_ext_control`

__u32 | `id` |  | Identifies the control, set by the application.
__u32 | `reserved2`[2] |  | 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.
| void * | `reserved` | Reserved for future pointer-type controls. Currently unused.

Table 2. struct `v4l2_ext_controls`

__u32 | `ctrl_class` | The control class to which all controls belong, see Table 3.
__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.
struct v4l2_ext_control * | `controls` | Pointer to an array of `count` v4l2_ext_control structures. Ignored if `count` equals zero.

Table 3. Control classes

`V4L2_CTRL_CLASS_USER` | 0x980000 | The class containing user controls. These controls are described in Section 1.8. 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 section Section 1.9.5.

## Return Value

On success 0 is returned, on error -1 and the `errno` variable is set appropriately:

EINVAL

  The struct v4l2_ext_control `id` is invalid or the struct 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 struct 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.

Prev | Home | Next
ioctl VIDIOC_G_ENC_INDEX | Up | ioctl VIDIOC_G_FBUF, VIDIOC_S_FBUF