net: core: Make the FIB notification chain generic

The FIB notification chain is currently soley used by IPv4 code.
However, we're going to introduce IPv6 FIB offload support, which
requires these notification as well.

As explained in commit c3852ef7f2f8 ("ipv4: fib: Replay events when
registering FIB notifier"), upon registration to the chain, the callee
receives a full dump of the FIB tables and rules by traversing all the
net namespaces. The integrity of the dump is ensured by a per-namespace
sequence counter that is incremented whenever a change to the tables or
rules occurs.

In order to allow more address families to use the chain, each family is
expected to register its fib_notifier_ops in its pernet init. These
operations allow the common code to read the family's sequence counter
as well as dump its tables and rules in the given net namespace.

Additionally, a 'family' parameter is added to sent notifications, so
that listeners could distinguish between the different families.

Implement the common code that allows listeners to register to the chain
and for address families to register their fib_notifier_ops. Subsequent
patches will implement these operations in IPv6.

In the future, ipmr and ip6mr will be extended to provide these
notifications as well.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 164 insertions, 0 deletions

diff --git a/net/core/fib_notifier.c b/net/core/fib_notifier.c
new file mode 100644
index 000000000000..292aab83702f
--- /dev/null
+++ b/net/core/fib_notifier.c
@@ -0,0 +1,164 @@
+#include <linux/rtnetlink.h>
+#include <linux/notifier.h>
+#include <linux/rcupdate.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <net/net_namespace.h>
+#include <net/fib_notifier.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);
+}
+EXPORT_SYMBOL(call_fib_notifier);
+
+int call_fib_notifiers(struct net *net, enum fib_event_type event_type,
+		       struct fib_notifier_info *info)
+{
+	info->net = net;
+	return atomic_notifier_call_chain(&fib_chain, event_type, info);
+}
+EXPORT_SYMBOL(call_fib_notifiers);
+
+static unsigned int fib_seq_sum(void)
+{
+	struct fib_notifier_ops *ops;
+	unsigned int fib_seq = 0;
+	struct net *net;
+
+	rtnl_lock();
+	for_each_net(net) {
+		list_for_each_entry(ops, &net->fib_notifier_ops, list)
+			fib_seq += ops->fib_seq_read(net);
+	}
+	rtnl_unlock();
+
+	return fib_seq;
+}
+
+static int fib_net_dump(struct net *net, struct notifier_block *nb)
+{
+	struct fib_notifier_ops *ops;
+
+	list_for_each_entry_rcu(ops, &net->fib_notifier_ops, list) {
+		int err = ops->fib_dump(net, nb);
+
+		if (err)
+			return err;
+	}
+
+	return 0;
+}
+
+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;
+	int err;
+
+	do {
+		unsigned int fib_seq = fib_seq_sum();
+		struct net *net;
+
+		rcu_read_lock();
+		for_each_net_rcu(net) {
+			err = fib_net_dump(net, nb);
+			if (err)
+				goto err_fib_net_dump;
+		}
+		rcu_read_unlock();
+
+		if (fib_dump_is_consistent(nb, cb, fib_seq))
+			return 0;
+	} while (++retries < FIB_DUMP_MAX_RETRIES);
+
+	return -EBUSY;
+
+err_fib_net_dump:
+	rcu_read_unlock();
+	return err;
+}
+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);
+
+static int __fib_notifier_ops_register(struct fib_notifier_ops *ops,
+				       struct net *net)
+{
+	struct fib_notifier_ops *o;
+
+	list_for_each_entry(o, &net->fib_notifier_ops, list)
+		if (ops->family == o->family)
+			return -EEXIST;
+	list_add_tail_rcu(&ops->list, &net->fib_notifier_ops);
+	return 0;
+}
+
+struct fib_notifier_ops *
+fib_notifier_ops_register(const struct fib_notifier_ops *tmpl, struct net *net)
+{
+	struct fib_notifier_ops *ops;
+	int err;
+
+	ops = kmemdup(tmpl, sizeof(*ops), GFP_KERNEL);
+	if (!ops)
+		return ERR_PTR(-ENOMEM);
+
+	err = __fib_notifier_ops_register(ops, net);
+	if (err)
+		goto err_register;
+
+	return ops;
+
+err_register:
+	kfree(ops);
+	return ERR_PTR(err);
+}
+EXPORT_SYMBOL(fib_notifier_ops_register);
+
+void fib_notifier_ops_unregister(struct fib_notifier_ops *ops)
+{
+	list_del_rcu(&ops->list);
+	kfree_rcu(ops, rcu);
+}
+EXPORT_SYMBOL(fib_notifier_ops_unregister);
+
+static int __net_init fib_notifier_net_init(struct net *net)
+{
+	INIT_LIST_HEAD(&net->fib_notifier_ops);
+	return 0;
+}
+
+static struct pernet_operations fib_notifier_net_ops = {
+	.init = fib_notifier_net_init,
+};
+
+static int __init fib_notifier_init(void)
+{
+	return register_pernet_subsys(&fib_notifier_net_ops);
+}
+
+subsys_initcall(fib_notifier_init);