#include <linux/rtnetlink.h>
#include <linux/notifier.h>
#include <linux/rcupdate.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <net/net_namespace.h>
#include <net/netns/generic.h>
#include <net/fib_notifier.h>

static unsigned int fib_notifier_net_id;

struct fib_notifier_net {
        struct list_head fib_notifier_ops;
        struct atomic_notifier_head fib_chain;
};

int call_fib_notifier(struct notifier_block *nb,
                      enum fib_event_type event_type,
                      struct fib_notifier_info *info)
{
        int err;

        err = nb->notifier_call(nb, event_type, info);
        return notifier_to_errno(err);
}
EXPORT_SYMBOL(call_fib_notifier);

int call_fib_notifiers(struct net *net, enum fib_event_type event_type,
                       struct fib_notifier_info *info)
{
        struct fib_notifier_net *fn_net = net_generic(net, fib_notifier_net_id);
        int err;

        err = atomic_notifier_call_chain(&fn_net->fib_chain, event_type, info);
        return notifier_to_errno(err);
}
EXPORT_SYMBOL(call_fib_notifiers);

static unsigned int fib_seq_sum(struct net *net)
{
        struct fib_notifier_net *fn_net = net_generic(net, fib_notifier_net_id);
        struct fib_notifier_ops *ops;
        unsigned int fib_seq = 0;

        rcu_read_lock();
        list_for_each_entry_rcu(ops, &fn_net->fib_notifier_ops, list) {
                if (!try_module_get(ops->owner))
                        continue;
                fib_seq += ops->fib_seq_read(net);
                module_put(ops->owner);
        }
        rcu_read_unlock();

        return fib_seq;
}

static int fib_net_dump(struct net *net, struct notifier_block *nb,
                        struct netlink_ext_ack *extack)
{
        struct fib_notifier_net *fn_net = net_generic(net, fib_notifier_net_id);
        struct fib_notifier_ops *ops;
        int err = 0;

        rcu_read_lock();
        list_for_each_entry_rcu(ops, &fn_net->fib_notifier_ops, list) {
                if (!try_module_get(ops->owner))
                        continue;
                err = ops->fib_dump(net, nb, extack);
                module_put(ops->owner);
                if (err)
                        goto unlock;
        }

unlock:
        rcu_read_unlock();

        return err;
}

static bool fib_dump_is_consistent(struct net *net, struct notifier_block *nb,
                                   void (*cb)(struct notifier_block *nb),
                                   unsigned int fib_seq)
{
        struct fib_notifier_net *fn_net = net_generic(net, fib_notifier_net_id);

        atomic_notifier_chain_register(&fn_net->fib_chain, nb);
        if (fib_seq == fib_seq_sum(net))
                return true;
        atomic_notifier_chain_unregister(&fn_net->fib_chain, nb);
        if (cb)
                cb(nb);
        return false;
}

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

        do {
                unsigned int fib_seq = fib_seq_sum(net);

                err = fib_net_dump(net, nb, extack);
                if (err)
                        return err;

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

        return -EBUSY;
}
EXPORT_SYMBOL(register_fib_notifier);

int unregister_fib_notifier(struct net *net, struct notifier_block *nb)
{
        struct fib_notifier_net *fn_net = net_generic(net, fib_notifier_net_id);

        return atomic_notifier_chain_unregister(&fn_net->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_net *fn_net = net_generic(net, fib_notifier_net_id);
        struct fib_notifier_ops *o;

        list_for_each_entry(o, &fn_net->fib_notifier_ops, list)
                if (ops->family == o->family)
                        return -EEXIST;
        list_add_tail_rcu(&ops->list, &fn_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)
{
        struct fib_notifier_net *fn_net = net_generic(net, fib_notifier_net_id);

        INIT_LIST_HEAD(&fn_net->fib_notifier_ops);
        ATOMIC_INIT_NOTIFIER_HEAD(&fn_net->fib_chain);
        return 0;
}

static void __net_exit fib_notifier_net_exit(struct net *net)
{
        struct fib_notifier_net *fn_net = net_generic(net, fib_notifier_net_id);

        WARN_ON_ONCE(!list_empty(&fn_net->fib_notifier_ops));
}

static struct pernet_operations fib_notifier_net_ops = {
        .init = fib_notifier_net_init,
        .exit = fib_notifier_net_exit,
        .id = &fib_notifier_net_id,
        .size = sizeof(struct fib_notifier_net),
};

static int __init fib_notifier_init(void)
{
        return register_pernet_subsys(&fib_notifier_net_ops);
}

subsys_initcall(fib_notifier_init);