#include <linux/workqueue.h>
#include <linux/rtnetlink.h>
#include <linux/cache.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/delay.h>
#include <linux/sched.h>
#include <net/net_namespace.h>

/*
 *	Our network namespace constructor/destructor lists
 */

static LIST_HEAD(pernet_list);
static struct list_head *first_device = &pernet_list;
static DEFINE_MUTEX(net_mutex);

LIST_HEAD(net_namespace_list);

static struct kmem_cache *net_cachep;

struct net init_net;
EXPORT_SYMBOL_GPL(init_net);

static struct net *net_alloc(void)
{
	return kmem_cache_zalloc(net_cachep, GFP_KERNEL);
}

static void net_free(struct net *net)
{
	if (!net)
		return;

	if (unlikely(atomic_read(&net->use_count) != 0)) {
		printk(KERN_EMERG "network namespace not free! Usage: %d\n",
			atomic_read(&net->use_count));
		return;
	}

	kmem_cache_free(net_cachep, net);
}

static void cleanup_net(struct work_struct *work)
{
	struct pernet_operations *ops;
	struct net *net;

	net = container_of(work, struct net, work);

	mutex_lock(&net_mutex);

	/* Don't let anyone else find us. */
	rtnl_lock();
	list_del(&net->list);
	rtnl_unlock();

	/* Run all of the network namespace exit methods */
	list_for_each_entry_reverse(ops, &pernet_list, list) {
		if (ops->exit)
			ops->exit(net);
	}

	mutex_unlock(&net_mutex);

	/* Ensure there are no outstanding rcu callbacks using this
	 * network namespace.
	 */
	rcu_barrier();

	/* Finally it is safe to free my network namespace structure */
	net_free(net);
}


void __put_net(struct net *net)
{
	/* Cleanup the network namespace in process context */
	INIT_WORK(&net->work, cleanup_net);
	schedule_work(&net->work);
}
EXPORT_SYMBOL_GPL(__put_net);

/*
 * setup_net runs the initializers for the network namespace object.
 */
static int setup_net(struct net *net)
{
	/* Must be called with net_mutex held */
	struct pernet_operations *ops;
	int error;

	atomic_set(&net->count, 1);
	atomic_set(&net->use_count, 0);

	error = 0;
	list_for_each_entry(ops, &pernet_list, list) {
		if (ops->init) {
			error = ops->init(net);
			if (error < 0)
				goto out_undo;
		}
	}
out:
	return error;

out_undo:
	/* Walk through the list backwards calling the exit functions
	 * for the pernet modules whose init functions did not fail.
	 */
	list_for_each_entry_continue_reverse(ops, &pernet_list, list) {
		if (ops->exit)
			ops->exit(net);
	}

	rcu_barrier();
	goto out;
}

struct net *copy_net_ns(unsigned long flags, struct net *old_net)
{
	struct net *new_net = NULL;
	int err;

	get_net(old_net);

	if (!(flags & CLONE_NEWNET))
		return old_net;

#ifndef CONFIG_NET_NS
	return ERR_PTR(-EINVAL);
#endif

	err = -ENOMEM;
	new_net = net_alloc();
	if (!new_net)
		goto out;

	mutex_lock(&net_mutex);
	err = setup_net(new_net);
	if (err)
		goto out_unlock;

	rtnl_lock();
	list_add_tail(&new_net->list, &net_namespace_list);
	rtnl_unlock();


out_unlock:
	mutex_unlock(&net_mutex);
out:
	put_net(old_net);
	if (err) {
		net_free(new_net);
		new_net = ERR_PTR(err);
	}
	return new_net;
}

static int __init net_ns_init(void)
{
	int err;

	printk(KERN_INFO "net_namespace: %zd bytes\n", sizeof(struct net));
	net_cachep = kmem_cache_create("net_namespace", sizeof(struct net),
					SMP_CACHE_BYTES,
					SLAB_PANIC, NULL);
	mutex_lock(&net_mutex);
	err = setup_net(&init_net);

	rtnl_lock();
	list_add_tail(&init_net.list, &net_namespace_list);
	rtnl_unlock();

	mutex_unlock(&net_mutex);
	if (err)
		panic("Could not setup the initial network namespace");

	return 0;
}

pure_initcall(net_ns_init);

static int register_pernet_operations(struct list_head *list,
				      struct pernet_operations *ops)
{
	struct net *net, *undo_net;
	int error;

	list_add_tail(&ops->list, list);
	if (ops->init) {
		for_each_net(net) {
			error = ops->init(net);
			if (error)
				goto out_undo;
		}
	}
	return 0;

out_undo:
	/* If I have an error cleanup all namespaces I initialized */
	list_del(&ops->list);
	if (ops->exit) {
		for_each_net(undo_net) {
			if (undo_net == net)
				goto undone;
			ops->exit(undo_net);
		}
	}
undone:
	return error;
}

static void unregister_pernet_operations(struct pernet_operations *ops)
{
	struct net *net;

	list_del(&ops->list);
	if (ops->exit)
		for_each_net(net)
			ops->exit(net);
}

/**
 *      register_pernet_subsys - register a network namespace subsystem
 *	@ops:  pernet operations structure for the subsystem
 *
 *	Register a subsystem which has init and exit functions
 *	that are called when network namespaces are created and
 *	destroyed respectively.
 *
 *	When registered all network namespace init functions are
 *	called for every existing network namespace.  Allowing kernel
 *	modules to have a race free view of the set of network namespaces.
 *
 *	When a new network namespace is created all of the init
 *	methods are called in the order in which they were registered.
 *
 *	When a network namespace is destroyed all of the exit methods
 *	are called in the reverse of the order with which they were
 *	registered.
 */
int register_pernet_subsys(struct pernet_operations *ops)
{
	int error;
	mutex_lock(&net_mutex);
	error =  register_pernet_operations(first_device, ops);
	mutex_unlock(&net_mutex);
	return error;
}
EXPORT_SYMBOL_GPL(register_pernet_subsys);

/**
 *      unregister_pernet_subsys - unregister a network namespace subsystem
 *	@ops: pernet operations structure to manipulate
 *
 *	Remove the pernet operations structure from the list to be
 *	used when network namespaces are created or destoryed.  In
 *	addition run the exit method for all existing network
 *	namespaces.
 */
void unregister_pernet_subsys(struct pernet_operations *module)
{
	mutex_lock(&net_mutex);
	unregister_pernet_operations(module);
	mutex_unlock(&net_mutex);
}
EXPORT_SYMBOL_GPL(unregister_pernet_subsys);

/**
 *      register_pernet_device - register a network namespace device
 *	@ops:  pernet operations structure for the subsystem
 *
 *	Register a device which has init and exit functions
 *	that are called when network namespaces are created and
 *	destroyed respectively.
 *
 *	When registered all network namespace init functions are
 *	called for every existing network namespace.  Allowing kernel
 *	modules to have a race free view of the set of network namespaces.
 *
 *	When a new network namespace is created all of the init
 *	methods are called in the order in which they were registered.
 *
 *	When a network namespace is destroyed all of the exit methods
 *	are called in the reverse of the order with which they were
 *	registered.
 */
int register_pernet_device(struct pernet_operations *ops)
{
	int error;
	mutex_lock(&net_mutex);
	error = register_pernet_operations(&pernet_list, ops);
	if (!error && (first_device == &pernet_list))
		first_device = &ops->list;
	mutex_unlock(&net_mutex);
	return error;
}
EXPORT_SYMBOL_GPL(register_pernet_device);

/**
 *      unregister_pernet_device - unregister a network namespace netdevice
 *	@ops: pernet operations structure to manipulate
 *
 *	Remove the pernet operations structure from the list to be
 *	used when network namespaces are created or destoryed.  In
 *	addition run the exit method for all existing network
 *	namespaces.
 */
void unregister_pernet_device(struct pernet_operations *ops)
{
	mutex_lock(&net_mutex);
	if (&ops->list == first_device)
		first_device = first_device->next;
	unregister_pernet_operations(ops);
	mutex_unlock(&net_mutex);
}
EXPORT_SYMBOL_GPL(unregister_pernet_device);