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

__u32id Identifies the control, set by the application.
__u32reserved2[2] Reserved for future extensions. Drivers and applications must set the array to zero.
union(anonymous)  
 __s32valueNew value or current value.
 __s64value64New value or current value.
 void *reservedReserved for future pointer-type controls. Currently unused.

Table 2. struct v4l2_ext_controls

__u32ctrl_classThe control class to which all controls belong, see Table 3.
__u32countThe number of controls in the controls array. May also be zero.
__u32error_idxSet 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).
__u32reserved[2]Reserved for future extensions. Drivers and applications must set the array to zero.
struct v4l2_ext_control *controlsPointer to an array of count v4l2_ext_control structures. Ignored if count equals zero.

Table 3. Control classes

V4L2_CTRL_CLASS_USER0x980000The 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_MPEG0x990000The 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.