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 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 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 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.