SHUTDOWNHOOK_ESTABLISH(9)				   BSD Kernel Developer's Manual				 SHUTDOWNHOOK_ESTABLISH(9)

NAME

     shutdownhook_establish, shutdownhook_disestablish -- add or remove a shutdown hook

SYNOPSIS

     void *
     shutdownhook_establish(void (*fn)(void *), void *arg);

     void
     shutdownhook_disestablish(void *cookie);

DESCRIPTION

     The shutdownhook_establish API is deprecated.

     The shutdownhook_establish() function adds fn to the list of hooks invoked by doshutdownhooks(9) at shutdown.  When invoked, the hook func-
     tion fn will be passed arg as its only argument.

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

     Shutdown hooks should be used to perform one-time activities that must happen immediately before the kernel exits.  Because of the environ-
     ment in which they are run, shutdown hooks cannot rely on many system services (including file systems, and timeouts and other interrupt-
     driven services), or even basic system integrity (because the system could be rebooting after a crash).

RETURN VALUES

     If successful, shutdownhook_establish() returns an opaque pointer describing the newly-established shutdown hook.	Otherwise, it returns
     NULL.

EXAMPLES

     It may be appropriate to use a shutdown hook to disable a device that does direct memory access, so that the device will not try to access
     memory while the system is rebooting.

     It may be appropriate to use a shutdown hook to inform watchdog timer hardware that the operating system is no longer running.

SEE ALSO

     doshutdownhooks(9)

BUGS

     The names are clumsy, at best.

BSD
								   May 14, 2009 							       BSD