SHUTDOWNHOOK_ESTABLIS... BSD Kernel Developer's ManualSHUTDOWNHOOK_ESTABLIS...NAME
shutdownhook_establish, shutdownhook_disestablish — add or remove a shut‐
down 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 shut‐
down. 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 environment
in which they are run, shutdown hooks cannot rely on many system services
(including file systems, and timeouts and other interrupt-driven ser‐
vices), 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 mem‐
ory 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 ALSOdoshutdownhooks(9)BUGS
The names are clumsy, at best.
BSD May 14, 2009 BSD
