SHUTDOWNHOOK_ESTABLISH(System Kernel Developer's ManuSHUTDOWNHOOK_ESTABLISH(9)
shutdownhook_establish, shutdownhook_disestablish - add or remove a shutdown
shutdownhook_establish(void (*fn)(void *), void *arg);
The shutdownhook_establish() function adds fn to the list of hooks
invoked by doshutdownhooks(9) at shutdown. When invoked, the hook function
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
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 services),
or even basic system integrity (because the system could be
rebooting after a crash).
If successful, shutdownhook_establish() returns an opaque pointer
describing the newly-established shutdown hook. Otherwise, it returns
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.
The names are clumsy, at best.
BSD November 13, 1995 BSD
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