Name

VIDIOC_G_PRIORITY, VIDIOC_S_PRIORITY — Query or request the access priority associated with a file descriptor

Synopsis

int ioctl(int fd,
 int request,
 enum v4l2_priority *argp);
 
int ioctl(int fd,
 int request,
 const enum v4l2_priority *argp);
 

Arguments

fd

File descriptor returned by open().

request

VIDIOC_G_PRIORITY, VIDIOC_S_PRIORITY

argp

Pointer to an enum v4l2_priority type.

Description

To query the current access priority applications call the VIDIOC_G_PRIORITY ioctl with a pointer to an enum v4l2_priority variable where the driver stores the current priority.

To request an access priority applications store the desired priority in an enum v4l2_priority variable and call VIDIOC_S_PRIORITY ioctl with a pointer to this variable.

Table A.82. enum v4l2_priority

V4L2_PRIORITY_UNSET0 
V4L2_PRIORITY_BACKGROUND1Lowest priority, usually applications running in background, for example monitoring VBI transmissions. A proxy application running in user space will be necessary if multiple applications want to read from a device at this priority.
V4L2_PRIORITY_INTERACTIVE2 
V4L2_PRIORITY_DEFAULT2Medium priority, usually applications started and interactively controlled by the user. For example TV viewers, Teletext browsers, or just "panel" applications to change the channel or video controls. This is the default priority unless an application requests another.
V4L2_PRIORITY_RECORD3Highest priority. Only one file descriptor can have this priority, it blocks any other fd from changing device properties. Usually applications which must not be interrupted, like video recording.

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 requested priority value is invalid.

EBUSY

Another application already requested higher priority.