fdFile descriptor returned by open().
requestVIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS, VIDIOC_TRY_EXT_CTRLS
argpThese 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. |
On success 0 is returned, on error -1 and the errno variable is set appropriately:
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.
The struct v4l2_ext_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.