SYSINIT relies on the ability of the linker to take static data declared at multiple
locations throughout a program's source and group it together as a single contiguous
chunk of data. This linker technique is called a ``linker set''. SYSINIT uses two linker
sets to maintain two data sets containing each consumer's call order, function, and a
pointer to the data to pass to that function.
SYSINIT uses two priorities when ordering the functions for execution. The first
priority is a subsystem ID giving an overall order for SYSINIT's dispatch of functions.
Current predeclared ID's are in <sys/kernel.h> in the
enum list sysinit_sub_id. The second priority used is an
element order within the subsystem. Current predeclared subsystem element orders are in
<sys/kernel.h> in the enum list sysinit_elem_order.
There are currently two uses for SYSINIT. Function dispatch at system startup and
kernel module loads, and function dispatch at system shutdown and kernel module unload.
Kernel subsystems often use system startup SYSINIT's to initialize data structures, for
example the process scheduling subsystem uses a SYSINIT to initialize the run queue data
structure. Device drivers should avoid using SYSINIT()
directly. Instead drivers for real devices that are part of a bus structure should use
DRIVER_MODULE() to provide a function that detects the device
and, if it is present, initializes the device. It will do a few things specific to
devices and then call SYSINIT() itself. For pseudo-devices,
which are not part of a bus structure, use DEV_MODULE().
