linux_kernel/net/ipv4/fib_notifier.c

#include <linux/rtnetlink.h>
#include <linux/notifier.h>
#include <linux/rcupdate.h>
#include <linux/kernel.h>
#include <net/net_namespace.h>
#include <net/netns/ipv4.h>
#include <net/ip_fib.h>

static ATOMIC_NOTIFIER_HEAD(fib_chain);

int call_fib_notifier(struct notifier_block *nb, struct net *net,
		      enum fib_event_type event_type,
		      struct fib_notifier_info *info)
{
	info->net = net;
	return nb->notifier_call(nb, event_type, info);
}

int call_fib_notifiers(struct net *net, enum fib_event_type event_type,
		       struct fib_notifier_info *info)
{
	net->ipv4.fib_seq++;
	info->net = net;
	return atomic_notifier_call_chain(&fib_chain, event_type, info);
}

static unsigned int fib_seq_sum(void)
{
	unsigned int fib_seq = 0;
	struct net *net;

	rtnl_lock();
	for_each_net(net)
		fib_seq += net->ipv4.fib_seq;
	rtnl_unlock();

	return fib_seq;
}

static bool fib_dump_is_consistent(struct notifier_block *nb,
				   void (*cb)(struct notifier_block *nb),
				   unsigned int fib_seq)
{
	atomic_notifier_chain_register(&fib_chain, nb);
	if (fib_seq == fib_seq_sum())
		return true;
	atomic_notifier_chain_unregister(&fib_chain, nb);
	if (cb)
		cb(nb);
	return false;
}

#define FIB_DUMP_MAX_RETRIES 5
int register_fib_notifier(struct notifier_block *nb,
			  void (*cb)(struct notifier_block *nb))
{
	int retries = 0;

	do {
		unsigned int fib_seq = fib_seq_sum();
		struct net *net;

		/* Mutex semantics guarantee that every change done to
		 * FIB tries before we read the change sequence counter
		 * is now visible to us.
		 */
		rcu_read_lock();
		for_each_net_rcu(net) {
			fib_rules_notify(net, nb);
			fib_notify(net, nb);
		}
		rcu_read_unlock();

		if (fib_dump_is_consistent(nb, cb, fib_seq))
			return 0;
	} while (++retries < FIB_DUMP_MAX_RETRIES);

	return -EBUSY;
}
EXPORT_SYMBOL(register_fib_notifier);

int unregister_fib_notifier(struct notifier_block *nb)
{
	return atomic_notifier_chain_unregister(&fib_chain, nb);
}
EXPORT_SYMBOL(unregister_fib_notifier);