POWERHOOK_ESTABLISH(9)

NAME
powerhook_establish, powerhook_disestablish - add or remove a power change hook

SYNOPSIS
void *
powerhook_establish(const char *name, void (*fn)(int why, void *a), void *arg);
void
powerhook_disestablish(void *cookie);

DESCRIPTION
The powerhook_establish() function adds fn of the list of hooks invoked by dopowerhooks(9) at power change. When invoked, the hook function fn will be passed the new power state as the first argument and arg as its second argument.

The powerhook_disestablish() function removes the hook described by the opaque pointer cookie from the list of hooks to be invoked at power change. If cookie is invalid, the result of powerhook_disestablish() is undefined.

Power hooks should be used to perform activities that must happen when the power situation to the computer changes. Because of the environment in which they are run, power hooks cannot rely on many system services (including file systems, and timeouts and other interrupt-driven services). The power hooks are typically executed from an interrupt context.

The different reasons for calling the power hooks are: suspend, standby, and resume. The reason is reflected in the why argument and the values PWR_SOFTSUSPEND, PWR_SUSPEND, PWR_SOFTSTANDBY, PWR_STANDBY, PWR_SOFTRESUME, and PWR_RESUME. It calls with PWR_SOFTxxx in the normal priority level while the other callings are protected with splhigh(9). At suspend the system is going to lose (almost) all power, standby retains some power (e.g., minimal power to USB devices), and at resume power is back to normal.

RETURN VALUES
If successful, powerhook_establish() returns an opaque pointer describing the newly-established power hook. Otherwise, it returns NULL.

SEE ALSO
dopowerhooks(9)