#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 <linux/idr.h>
#include <net/net_namespace.h>
#include <net/netns/generic.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);
EXPORT_SYMBOL_GPL(net_namespace_list);

struct net init_net;
EXPORT_SYMBOL(init_net);

#define INITIAL_NET_GEN_PTRS    13 /* +1 for len +2 for rcu_head */

/*
 * 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 = 0;

        atomic_set(&net->count, 1);

#ifdef NETNS_REFCNT_DEBUG
        atomic_set(&net->use_count, 0);
#endif

        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;
}

static struct net_generic *net_alloc_generic(void)
{
        struct net_generic *ng;
        size_t generic_size = sizeof(struct net_generic) +
                INITIAL_NET_GEN_PTRS * sizeof(void *);

        ng = kzalloc(generic_size, GFP_KERNEL);
        if (ng)
                ng->len = INITIAL_NET_GEN_PTRS;

        return ng;
}

#ifdef CONFIG_NET_NS
static struct kmem_cache *net_cachep;
static struct workqueue_struct *netns_wq;

static struct net *net_alloc(void)
{
        struct net *net = NULL;
        struct net_generic *ng;

        ng = net_alloc_generic();
        if (!ng)
                goto out;

        net = kmem_cache_zalloc(net_cachep, GFP_KERNEL);
        if (!net)
                goto out_free;

        rcu_assign_pointer(net->gen, ng);
out:
        return net;

out_free:
        kfree(ng);
        goto out;
}

static void net_free(struct net *net)
{
#ifdef NETNS_REFCNT_DEBUG
        if (unlikely(atomic_read(&net->use_count) != 0)) {
                printk(KERN_EMERG "network namespace not free! Usage: %d\n",
                        atomic_read(&net->use_count));
                return;
        }
#endif
        kfree(net->gen);
        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_err;

        mutex_lock(&net_mutex);
        err = setup_net(new_net);
        if (!err) {
                rtnl_lock();
                list_add_tail(&new_net->list, &net_namespace_list);
                rtnl_unlock();
        }
        mutex_unlock(&net_mutex);

        if (err)
                goto out_free;
out:
        put_net(old_net);
        return new_net;

out_free:
        net_free(new_net);
out_err:
        new_net = ERR_PTR(err);
        goto out;
}

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);
        queue_work(netns_wq, &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)
{
        struct net_generic *ng;
        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);

        /* Create workqueue for cleanup */
        netns_wq = create_singlethread_workqueue("netns");
        if (!netns_wq)
                panic("Could not create netns workq");
#endif

        ng = net_alloc_generic();
        if (!ng)
                panic("Could not allocate generic netns");

        rcu_assign_pointer(init_net.gen, ng);

        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

static DEFINE_IDA(net_generic_ids);

/**
 *      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 destroyed.  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);

int register_pernet_gen_subsys(int *id, struct pernet_operations *ops)
{
        int rv;

        mutex_lock(&net_mutex);
again:
        rv = ida_get_new_above(&net_generic_ids, 1, id);
        if (rv < 0) {
                if (rv == -EAGAIN) {
                        ida_pre_get(&net_generic_ids, GFP_KERNEL);
                        goto again;
                }
                goto out;
        }
        rv = register_pernet_operations(first_device, ops);
        if (rv < 0)
                ida_remove(&net_generic_ids, *id);
out:
        mutex_unlock(&net_mutex);
        return rv;
}
EXPORT_SYMBOL_GPL(register_pernet_gen_subsys);

void unregister_pernet_gen_subsys(int id, struct pernet_operations *ops)
{
        mutex_lock(&net_mutex);
        unregister_pernet_operations(ops);
        ida_remove(&net_generic_ids, id);
        mutex_unlock(&net_mutex);
}
EXPORT_SYMBOL_GPL(unregister_pernet_gen_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);

int register_pernet_gen_device(int *id, struct pernet_operations *ops)
{
        int error;
        mutex_lock(&net_mutex);
again:
        error = ida_get_new_above(&net_generic_ids, 1, id);
        if (error) {
                if (error == -EAGAIN) {
                        ida_pre_get(&net_generic_ids, GFP_KERNEL);
                        goto again;
                }
                goto out;
        }
        error = register_pernet_operations(&pernet_list, ops);
        if (error)
                ida_remove(&net_generic_ids, *id);
        else if (first_device == &pernet_list)
                first_device = &ops->list;
out:
        mutex_unlock(&net_mutex);
        return error;
}
EXPORT_SYMBOL_GPL(register_pernet_gen_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 destroyed.  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);

void unregister_pernet_gen_device(int id, struct pernet_operations *ops)
{
        mutex_lock(&net_mutex);
        if (&ops->list == first_device)
                first_device = first_device->next;
        unregister_pernet_operations(ops);
        ida_remove(&net_generic_ids, id);
        mutex_unlock(&net_mutex);
}
EXPORT_SYMBOL_GPL(unregister_pernet_gen_device);

static void net_generic_release(struct rcu_head *rcu)
{
        struct net_generic *ng;

        ng = container_of(rcu, struct net_generic, rcu);
        kfree(ng);
}

int net_assign_generic(struct net *net, int id, void *data)
{
        struct net_generic *ng, *old_ng;

        BUG_ON(!mutex_is_locked(&net_mutex));
        BUG_ON(id == 0);

        ng = old_ng = net->gen;
        if (old_ng->len >= id)
                goto assign;

        ng = kzalloc(sizeof(struct net_generic) +
                        id * sizeof(void *), GFP_KERNEL);
        if (ng == NULL)
                return -ENOMEM;

        /*
         * Some synchronisation notes:
         *
         * The net_generic explores the net->gen array inside rcu
         * read section. Besides once set the net->gen->ptr[x]
         * pointer never changes (see rules in netns/generic.h).
         *
         * That said, we simply duplicate this array and schedule
         * the old copy for kfree after a grace period.
         */

        ng->len = id;
        memcpy(&ng->ptr, &old_ng->ptr, old_ng->len);

        rcu_assign_pointer(net->gen, ng);
        call_rcu(&old_ng->rcu, net_generic_release);
assign:
        ng->ptr[id - 1] = data;
        return 0;
}
EXPORT_SYMBOL_GPL(net_assign_generic);