#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);

struct net init_net;
EXPORT_SYMBOL(init_net);

/*
 * setup_net runs the initializers for the network namespace object.
 */
static __net_init 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;
}

#ifdef CONFIG_NET_NS
static struct kmem_cache *net_cachep;

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);
}

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;

        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 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);

#else
struct net *copy_net_ns(unsigned long flags, struct net *old_net)
{
        if (flags & CLONE_NEWNET)
                return ERR_PTR(-EINVAL);
        return old_net;
}
#endif

static int __init net_ns_init(void)
{
        int err;

        printk(KERN_INFO "net_namespace: %zd bytes\n", sizeof(struct net));
#ifdef CONFIG_NET_NS
        net_cachep = kmem_cache_create("net_namespace", sizeof(struct net),
                                        SMP_CACHE_BYTES,
                                        SLAB_PANIC, NULL);
#endif
        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);

#ifdef CONFIG_NET_NS
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);
}

#else

static int register_pernet_operations(struct list_head *list,
                                      struct pernet_operations *ops)
{
        if (ops->init == NULL)
                return 0;
        return ops->init(&init_net);
}

static void unregister_pernet_operations(struct pernet_operations *ops)
{
        if (ops->exit)
                ops->exit(&init_net);
}
#endif

/**
 *      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);