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SYSINIT(9)	       FreeBSD Kernel Developer's Manual	    SYSINIT(9)

     SYSINIT, SYSUNINIT	-- a framework for dynamic kernel initialization

     #include <sys/param.h>
     #include <sys/kernel.h>

     SYSINIT(uniquifier, enum sysinit_sub_id subsystem,
	 enum sysinit_elem_order order,	sysinit_cfunc_t	func,
	 const void *ident);

     SYSUNINIT(uniquifier, enum	sysinit_sub_id subsystem,
	 enum sysinit_elem_order order,	sysinit_cfunc_t	func,
	 const void *ident);

     SYSINIT is	a mechanism for	scheduling the execution of initialization and
     teardown routines.	 This is similar to init and fini routines with	the
     addition of explicit ordering metadata.  It allows	runtime	ordering of
     subsystem initialization in the kernel as well as kernel modules (KLDs).

     The SYSINIT() macro creates a struct sysinit and stores it	in a startup
     linker set.  The struct sysinit type as well as the subsystem identifier
     constants (SI_SUB_*) and initialization ordering constants	(SI_ORDER_*)
     are defined in <sys/kernel.h>:

     struct sysinit {
	     enum sysinit_sub_id subsystem;  /*	subsystem identifier*/
	     enum sysinit_elem_order order;  /*	init order within subsystem*/
	     sysinit_cfunc_t func;	     /*	function	     */
	     const void	     *udata;	     /*	multiplexer/argument */

     The SYSINIT() macro takes a uniquifier argument to	identify the particu-
     lar function dispatch data, the subsystem type of startup interface, the
     subsystem element order of	initialization within the subsystem, the func
     function to call, and the data specified in ident argument	to pass	the

     The SYSUNINIT() macro behaves similarly to	the SYSINIT() macro except
     that it adds the data to a	shutdown linker	set.

     The startup linker	set for	the kernel is scanned during boot to build a
     sorted list of initialization routines.  The initialization routines are
     then executed in the sorted order.	 The subsystem is used as the primary
     key and is	sorted in ascending order.  The	order is used as the secondary
     key and is	sorted in ascending order.  The	relative order of two routines
     that have the same	subsystem and order is undefined.

     The startup linker	sets for modules that are loaded together with the
     kernel by the boot	loader are scanned during the SI_SUB_KLD subsystem
     initialization.  These modules' initialization routines are sorted	and
     merged into the kernel's list of startup routines and are executed	during
     boot along	with the kernel's initialization routines.  Note that this has
     the effect	that any initialization	routines in a kernel module that are
     scheduled earlier than SI_SUB_KLD are not executed	until after SI_SUB_KLD
     during boot.

     The startup linker	set for	a kernel module	loaded at runtime via
     kldload(2)	is scanned, sorted, and	executed when the module is loaded.

     The shutdown linker set for a kernel module is scanned, sorted, and exe-
     cuted when	a kernel module	is unloaded.  The teardown routines are	sorted
     in	the reverse order of the initialization	routines.  The teardown	rou-
     tines of the kernel and any loaded	modules	are not	executed during	shut-

     This example shows	the SYSINIT which displays the copyright notice	during

	   static void
	   print_caddr_t(void *data)
		   printf("%s",	(char *)data);
	   SYSINIT(announce, SI_SUB_COPYRIGHT, SI_ORDER_FIRST, print_caddr_t,


     The SYSINIT framework first appeared in FreeBSD 2.2.

     The SYSINIT framework was written by Terrence Lambert

     This manual page was written by Hiten Pandya <>.

FreeBSD	11.0		       December	1, 2010			  FreeBSD 11.0


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