9.2. Dynamic Kernel Linker Facility - KLD
The kld interface allows system administrators to
dynamically add and remove functionality from a running system.
This allows device driver writers to load their new changes into
a running kernel without constantly rebooting to test
changes.
The kld interface is used through:
kldload
- loads a new kernel
modulekldunload
- unloads a kernel
modulekldstat
- lists loaded
modules
Skeleton Layout of a kernel module
/*
* KLD Skeleton
* Inspired by Andrew Reiter's Daemonnews article
*/
#include <sys/types.h>
#include <sys/module.h>
#include <sys/systm.h> /* uprintf */
#include <sys/errno.h>
#include <sys/param.h> /* defines used in kernel.h */
#include <sys/kernel.h> /* types used in module initialization */
/*
* Load handler that deals with the loading and unloading of a KLD.
*/
static int
skel_loader(struct module *m, int what, void *arg)
{
int err = 0;
switch (what) {
case MOD_LOAD: /* kldload */
uprintf("Skeleton KLD loaded.\n");
break;
case MOD_UNLOAD:
uprintf("Skeleton KLD unloaded.\n");
break;
default:
err = EOPNOTSUPP;
break;
}
return(err);
}
/* Declare this module to the rest of the kernel */
static moduledata_t skel_mod = {
"skel",
skel_loader,
NULL
};
DECLARE_MODULE(skeleton, skel_mod, SI_SUB_KLD, SI_ORDER_ANY);
FreeBSD provides a system makefile to simplify compiling a
kernel module.
SRCS=skeleton.c
KMOD=skeleton
.include <bsd.kmod.mk>
Running make
with this makefile
will create a file skeleton.ko
that can
be loaded into the kernel by typing:
#
kldload -v ./skeleton.ko