SHUTDOWNHOOK_ESTABLISH(System Kernel Developer's ManuSHUTDOWNHOOK_ESTABLISH(9)

NAME    [Toc]    [Back]

     shutdownhook_establish, shutdownhook_disestablish - add or remove a shutdown
 hook

SYNOPSIS    [Toc]    [Back]

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

     void
     shutdownhook_disestablish(void *cookie);

DESCRIPTION    [Toc]    [Back]

     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    [Toc]    [Back]

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

EXAMPLES    [Toc]    [Back]

     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    [Toc]    [Back]

     doshutdownhooks(9)

BUGS    [Toc]    [Back]

     The names are clumsy, at best.

BSD                            November 13, 1995                           BSD