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.Dd September 29, 2010
.Dt SYSINIT 9
.Os
.Sh NAME
.Nm SYSINIT
.Nd Subsystem initialization
.Sh SYNOPSIS
.In sys/kernel.h
.Fn SYSINIT "uniquifier" "subsystem" "order" "func" "ident"
.Sh DESCRIPTION
.Nm
is a mechanism used in the initialization of kernel subsystems.
The function
.Fa func
is called with the argument
.Fa ident
either when the kernel is booted or when a module is loaded, depending on where
the invocation is found.
.Pp
The
.Fa subsystem
and
.Fa order
parameters control when the function is called during initialization.
The kernel
calls all of the functions in a subsystem before advancing to the next one.
.Pp
Most
.Nm
invocations will use one of these identifiers for
.Fa subsystem :
.Bl -tag -width ".Dv SI_SUB_HELPER_THREADS"
.It Dv SI_SUB_DRIVERS
Device driver initialization
.It Dv SI_SUB_VFS
Virtual file system, vnodes, vnode recovery, namecache
.It Dv SI_SUB_HELPER_THREADS
Helper threads (used by random number generator)
.It DV SI_SUB_KTHREAD_VM
VM daemon initialization
.It Dv SI_SUB_KTHREAD_IDLE
Idle-time kernel threads
.El
.Pp
These subsystems are initialized in the order they are listed.
For the complete list of subsystems, consult
.In sys/kernel.h .
.Pp
The
.Fa order
parameter controls when in a subsystem a function is called.
The
.Dv SI_ORDER_FIRST
parameter marks a function to be called first in subsystem.
The
.Dv SI_ORDER_SECOND
and
.Dv SI_ORDER_THIRD
flags mark a function to be called second and third, respectively.
The
.Dv SI_ORDER_MIDDLE
flag marks a function to be called somewhere in the middle of a
subsystem's initialization.
The
.Dv SI_ORDER_ANY
flag marks a function to be called after all other types of functions.
.Pp
The
.Fa uniquifier
parameter is a unique identifier for this
.Nm
invocation.
.Sh EXAMPLES
This example calls the function
.Fn rand_thread_init
with a
.Dv NULL
argument at any point while initializing helper threads:
.Bd -literal
SYSINIT(rand, SI_SUB_HELPER_THREADS, SI_ORDER_ANY, rand_thread_init, NULL);
.Ed