POWERHOOK_ESTABLISH(9)					   BSD Kernel Developer's Manual				    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 API is deprecated.

     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 environ-
     ment 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)

BSD
								   May 14, 2009 							       BSD