shutdownhook_establish(9) - NetBSD Manual Pages

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SHUTDOWNHOOK_ESTABLISH(9)    NetBSD Kernel Manual    SHUTDOWNHOOK_ESTABLISH(9)


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() function adds fn to the list of hooks in-
     voked 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 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 re-
     booting after a crash).


RETURN VALUES

     If successful, shutdownhook_establish() returns an opaque pointer de-
     scribing 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 ALSO

     doshutdownhooks(9)


BUGS

     The names are clumsy, at best.

NetBSD 1.6                     November 13, 1995                             1