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


SYSINIT, SYSUNINITa 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 shutdown.


This example shows the SYSINIT which displays the copyright notice during boot:

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 <terry@FreeBSD.org>.

This manual page was written by Hiten Pandya <hmp@FreeBSD.org>.

December 1, 2010 FreeBSD