VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS, VIDIOC_TRY_EXT_CTRLS — Get or set the value of several controls, try control values
int ioctl( | int | fd, |
| int | request, | |
| struct v4l2_ext_controls * | argp); |
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 80, “Control classes”) 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,
size and reserved2 fields
of each struct v4l2_ext_control and call the
VIDIOC_G_EXT_CTRLS ioctl. String controls controls
must also set the string field.
If the size is too small to
receive the control result (only relevant for pointer-type controls
like strings), then the driver will set size
to a valid value and return an ENOSPC error code. You should re-allocate the
string memory to this new size and try again. It is possible that the
same issue occurs again if the string has grown in the meantime. It is
recommended to call VIDIOC_QUERYCTRL first and use
maximum+1 as the new size
value. It is guaranteed that that is sufficient memory.
To change the value of a set of controls applications
initialize the id, size,
reserved2 and
value/string fields of each 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 a set of controls have correct values applications
initialize the id, size,
reserved2 and
value/string fields of each 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 78. struct v4l2_ext_control
| __u32 | id | Identifies the control, set by the application. | |
| __u32 | size | The total size in bytes of the payload of this
control. This is normally 0, but for pointer controls this should be
set to the size of the memory containing the payload, or that will
receive the payload. If VIDIOC_G_EXT_CTRLS finds
that this value is less than is required to store
the payload result, then it is set to a value large enough to store the
payload result and ENOSPC is returned. Note that for string controls
this size field should not be confused with the length of the string.
This field refers to the size of the memory that contains the string.
The actual length of the string may well be much smaller.
| |
| __u32 | reserved2[1] | 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. | |
| char * | string | A pointer to a string. |
Table 79. struct v4l2_ext_controls
| __u32 | ctrl_class | The control class to which all controls belong, see Table 80, “Control classes”. |
| __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 80. Control classes
V4L2_CTRL_CLASS_USER | 0x980000 | The class containing user controls. These controls
are described in Section 1.8, “User Controls”. 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 1.9.5, “MPEG Control Reference”. |
V4L2_CTRL_CLASS_CAMERA | 0x9a0000 | The class containing camera controls. These controls are described in Section 1.9.6, “Camera Control Reference”. |
V4L2_CTRL_CLASS_FM_TX | 0x9b0000 | The class containing FM Transmitter (FM TX) controls. These controls are described in Section 1.9.7, “FM Transmitter Control Reference”. |
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.
The space reserved for the control's payload is insufficient.
The field size is set to a value that is enough
to store the payload and this error code is returned.