7.25.1. Name

VIDIOC_G_CTRL - VIDIOC_S_CTRL - Get or set the value of a control

7.25.2. Synopsis

int ioctl(int fd, VIDIOC_G_CTRL, struct v4l2_control *argp)
int ioctl(int fd, VIDIOC_S_CTRL, struct v4l2_control *argp)

7.25.3. Arguments

File descriptor returned by open().
Pointer to struct v4l2_control.

7.25.4. 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.

struct v4l2_control
__u32 id Identifies the control, set by the application.
__s32 value New value or current value.

7.25.5. 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.

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).
The struct v4l2_control value is out of bounds.
The control is temporarily not changeable, possibly because another applications took over control of the device function this control belongs to.
Attempt to set a read-only control or to get a write-only control.