<< Back to man.ChinaUnix.net

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 the following privileged commands:



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 = EINVAL;
    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);

9.2.1 Makefile

FreeBSD provides a makefile include that you can use to quickly compile your kernel addition.

SRCS=skeleton.c
KMOD=skeleton

.include <bsd.kmod.mk>

Simply running make with this makefile will create a file skeleton.ko that can be loaded into your system by typing:

# kldload -v ./skeleton.ko


This, and other documents, can be downloaded from ftp://ftp.FreeBSD.org/pub/FreeBSD/doc/.

For questions about FreeBSD, read the documentation before contacting <questions@FreeBSD.org>.
For questions about this documentation, e-mail <doc@FreeBSD.org>.