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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
     particular 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 function.

     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
     executed when a kernel module is unloaded.  The teardown routines are
     sorted in the reverse order of the initialization routines.  The teardown
     routines of the kernel and any loaded modules are not executed during

     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-PRERELEASE        December 1, 2010        FreeBSD 11.0-PRERELEASE


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