Notifier Chains

 

Essential linux device driver:

 

Notifier chains are used to send status change messges to code regions that request them.

There are Die notification, Net device notification,  CPU frequency notification, and Internet address notification.

To attach your code to a notifier chain, you have to register an event handler with the associated chain.

 

Example:

 

//notifier.c#include <linux/notifier.h>//#include <asm/kdebug.h>#include <linux/kdebug.h>#include <linux/netdevice.h>#include <linux/inetdevice.h>MODULE_LICENSE("Dual BSD/GPL");int my_die_event_handler(struct notifier_block *self,unsigned long val, void* data);int my_dev_event_handler(struct notifier_block *self,unsigned long val, void* data);int my_event_handler(struct notifier_block *self,unsigned long val, void *data);// Die notifier Definitionstatic struct notifier_block my_die_notifier = {.notifier_call = my_die_event_handler,};//Die notification envent handlerint my_die_event_handler(struct notifier_block *self,unsigned long val, void* data){struct die_args *args = (struct die_args*)data;args = args;if (val == 1) {printk("%s: OOPs! EIP = %lx, ESP= %lx/n", __func__, (long)(args->regs->eip),(long) ( args->regs->esp));}return 0;}// Net device notifier definitionstatic struct notifier_block my_dev_notifier = {.notifier_call = my_dev_event_handler,};// Net Device notification event handlerint my_dev_event_handler(struct notifier_block *self,unsigned long val, void* data){printk(KERN_EMERG "%s: Val=%ld, Interface = %s/n", __func__, val, ((struct net_device *)data)->name);return 0;}// User defined notifier chain implementationstatic BLOCKING_NOTIFIER_HEAD(my_noti_chain);// what's this used forstatic struct notifier_block my_notifier = {.notifier_call = my_event_handler,};// User defined notification event handlerint my_event_handler(struct notifier_block *self,unsigned long val, void *data){printk("%s: Val=%ld /n", __func__, val);return 0;}static int mydrv_init(void){printk("Hello, beatiful new world!/n");// Register die notiferregister_die_notifier(&my_die_notifier);// Register Net device notiferregister_netdevice_notifier(&my_dev_notifier);// Register a user-defined notifierblocking_notifier_chain_register(&my_noti_chain,&my_notifier);return 0;}static void mydrv_exit(void){printk("Bye, my dear!/n Cruel world/n");unregister_die_notifier(&my_die_notifier);unregister_netdevice_notifier(&my_dev_notifier);blocking_notifier_chain_unregister(&my_noti_chain,&my_notifier);}module_init(mydrv_init);module_exit(mydrv_exit);