Notifier chains

[Adel Qodmani]

On Tue, Jul 23, 2013 at 7:21 AM, PV Juliet <pvjuliet at gmail.com> wrote:

> Hi,
>  Thanks for the reply . Can you tell me how i can subscribe to notifier
> chains when  IP address changes in a system ? What are all the steps to
> make it work??
>
> Thanks and Regards
> Juliet
>

Hey Juliet,

Well, let me start by just reminding you of a fact:
An NIC is represented in the system by the net_device structure so that's
the first clue.
What we want to do is to let the kernel notify us when a change happens
over the net_device; then we'll check which net_device it is
and was the event.

Declare a variable of type notifier_block:
*/* Create a notifier variable and let its notifier_call function pointer
point to our handler */*
*struct notifier_block my_notifier =
{*
*    .notifier_call = my_handler_function,*
*};*

The handler function HAS to have the following signature:
*int my_handler_function(struct notifier_block *self, unsigned long
notification, void *data);*

Next you want to register the notifier so that the kernel will call it when
an event happens: (most likely, you should have this in the module_init
code)
*register_netdevice_notifier(&my_notifier);*
When you're done with it (probably in the module_exit), do not forget to
remove it:
*unregister_netdevice_notifier(&my_notifier);*
*
*
Now what's left is how you'll know which event happened, because your
handler is gonna get called when so many events happen:
here's a sample code for the my_notifier that checks if the IP changed and
if it did, it logs this

*int my_handler_function(struct notifier_block *self, unsigned long
notification, void *data)
{*
*    struct net_device *dev;*
*    /* To see what kind of events you can check, refer to the netdevice.h
file */*
*    if(notification != NETDEV_CHANGEADDR)
        return something;*
*     dev = data;*
*     printk("Device %s has changed its IP address\n", dev->name);
}*
*
*
Let us know if you have any more questions,

Regards
Adel

P.S It's generally considered a bad practice to top-post the reply.
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