Name

VIDIOC_G_CTRL, VIDIOC_S_CTRL — Get or set the value of a control

Synopsis

int ioctl(int fd,
 int request,
 struct v4l2_control *argp);
 

Arguments

fd

File descriptor returned by open().

request

VIDIOC_G_CTRL, VIDIOC_S_CTRL

argp

Description

To get the current value of a control applications initialize the id field of a struct v4l2_control and call the VIDIOC_G_CTRL ioctl with a pointer to this structure. To change the value of a control applications initialize the id and value fields of a struct v4l2_control and call the VIDIOC_S_CTRL ioctl.

When the id 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. However, VIDIOC_S_CTRL is a write-only ioctl, it does not return the actual new value. If the value is inappropriate for the control (e.g. if it refers to an unsupported menu index of a menu control), then EINVAL error code is returned as well.

These ioctls work only with user controls. For other control classes the VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS or VIDIOC_TRY_EXT_CTRLS must be used.

Table A.55. struct v4l2_control

__u32idIdentifies the control, set by the application.
__s32valueNew value or current value.

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 Generic Error Codes chapter.

EINVAL

The struct v4l2_control id is invalid or the value is inappropriate for the given control (i.e. if a menu item is selected that is not supported by the driver according to VIDIOC_QUERYMENU).

ERANGE

The struct v4l2_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.

EACCES

Attempt to set a read-only control or to get a write-only control.