/*
 * net/core/dst.c       Protocol independent destination cache.
 *
 * Authors:             Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
 *
 */

#include <linux/bitops.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/workqueue.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/netdevice.h>
#include <linux/skbuff.h>
#include <linux/string.h>
#include <linux/types.h>
#include <net/net_namespace.h>
#include <linux/sched.h>
#include <linux/prefetch.h>
#ifndef __GENKSYMS__
#include <net/lwtunnel.h>
#endif

#include <net/dst.h>
#include <net/dst_metadata.h>

/*
 * Theory of operations:
 * 1) We use a list, protected by a spinlock, to add
 *    new entries from both BH and non-BH context.
 * 2) In order to keep spinlock held for a small delay,
 *    we use a second list where are stored long lived
 *    entries, that are handled by the garbage collect thread
 *    fired by a workqueue.
 * 3) This list is guarded by a mutex,
 *    so that the gc_task and dst_dev_event() can be synchronized.
 */

/*
 * We want to keep lock & list close together
 * to dirty as few cache lines as possible in __dst_free().
 * As this is not a very strong hint, we dont force an alignment on SMP.
 */
static struct {
        spinlock_t              lock;
        struct dst_entry        *list;
        unsigned long           timer_inc;
        unsigned long           timer_expires;
} dst_garbage = {
        .lock = __SPIN_LOCK_UNLOCKED(dst_garbage.lock),
        .timer_inc = DST_GC_MAX,
};
static void dst_gc_task(struct work_struct *work);
static void ___dst_free(struct dst_entry *dst);

static DECLARE_DELAYED_WORK(dst_gc_work, dst_gc_task);

static DEFINE_MUTEX(dst_gc_mutex);
/*
 * long lived entries are maintained in this list, guarded by dst_gc_mutex
 */
static struct dst_entry         *dst_busy_list;

static void dst_gc_task(struct work_struct *work)
{
        int    delayed = 0;
        int    work_performed = 0;
        unsigned long expires = ~0L;
        struct dst_entry *dst, *next, head;
        struct dst_entry *last = &head;

        mutex_lock(&dst_gc_mutex);
        next = dst_busy_list;

loop:
        while ((dst = next) != NULL) {
                next = dst->next;
                prefetch(&next->next);
                cond_resched();
                if (likely(atomic_read(&dst->__refcnt))) {
                        last->next = dst;
                        last = dst;
                        delayed++;
                        continue;
                }
                work_performed++;

                dst = dst_destroy(dst);
                if (dst) {
                        /* NOHASH and still referenced. Unless it is already
                         * on gc list, invalidate it and add to gc list.
                         *
                         * Note: this is temporary. Actually, NOHASH dst's
                         * must be obsoleted when parent is obsoleted.
                         * But we do not have state "obsoleted, but
                         * referenced by parent", so it is right.
                         */
                        if (dst->obsolete > 0)
                                continue;

                        ___dst_free(dst);
                        dst->next = next;
                        next = dst;
                }
        }

        spin_lock_bh(&dst_garbage.lock);
        next = dst_garbage.list;
        if (next) {
                dst_garbage.list = NULL;
                spin_unlock_bh(&dst_garbage.lock);
                goto loop;
        }
        last->next = NULL;
        dst_busy_list = head.next;
        if (!dst_busy_list)
                dst_garbage.timer_inc = DST_GC_MAX;
        else {
                /*
                 * if we freed less than 1/10 of delayed entries,
                 * we can sleep longer.
                 */
                if (work_performed <= delayed/10) {
                        dst_garbage.timer_expires += dst_garbage.timer_inc;
                        if (dst_garbage.timer_expires > DST_GC_MAX)
                                dst_garbage.timer_expires = DST_GC_MAX;
                        dst_garbage.timer_inc += DST_GC_INC;
                } else {
                        dst_garbage.timer_inc = DST_GC_INC;
                        dst_garbage.timer_expires = DST_GC_MIN;
                }
                expires = dst_garbage.timer_expires;
                /*
                 * if the next desired timer is more than 4 seconds in the
                 * future then round the timer to whole seconds
                 */
                if (expires > 4*HZ)
                        expires = round_jiffies_relative(expires);
                schedule_delayed_work(&dst_gc_work, expires);
        }

        spin_unlock_bh(&dst_garbage.lock);
        mutex_unlock(&dst_gc_mutex);
}

int dst_discard_sk(struct sock *sk, struct sk_buff *skb)
{
        kfree_skb(skb);
        return 0;
}
EXPORT_SYMBOL(dst_discard_sk);

const struct dst_metrics dst_default_metrics = {
        /* This initializer is needed to force linker to place this variable
         * into const section. Otherwise it might end into bss section.
         * We really want to avoid false sharing on this variable, and catch
         * any writes on it.
         */
        .refcnt = ATOMIC_INIT(1),
};

void dst_init(struct dst_entry *dst, struct dst_ops *ops,
              struct net_device *dev, int initial_ref, int initial_obsolete,
              unsigned short flags)
{
        dst->child = NULL;
        dst->dev = dev;
        if (dev)
                dev_hold(dev);
        dst->ops = ops;
        dst_init_metrics(dst, dst_default_metrics.metrics, true);
        dst->expires = 0UL;
        dst->path = dst;
        dst->from = NULL;
#ifdef CONFIG_XFRM
        dst->xfrm = NULL;
#endif
        dst->input = dst_discard;
        dst->output = dst_discard_sk;
        dst->error = 0;
        dst->obsolete = initial_obsolete;
        dst->header_len = 0;
        dst->trailer_len = 0;
#ifdef CONFIG_IP_ROUTE_CLASSID
        dst->tclassid = 0;
#endif
        dst->lwtstate = NULL;
        atomic_set(&dst->__refcnt, initial_ref);
        dst->__use = 0;
        dst->lastuse = jiffies;
        dst->flags = flags;
        dst->next = NULL;
        if (!(flags & DST_NOCOUNT))
                dst_entries_add(ops, 1);
}
EXPORT_SYMBOL(dst_init);

void *dst_alloc(struct dst_ops *ops, struct net_device *dev,
                int initial_ref, int initial_obsolete, unsigned short flags)
{
        struct dst_entry *dst;

        if (ops->gc && dst_entries_get_fast(ops) > ops->gc_thresh) {
                if (ops->gc(ops))
                        return NULL;
        }

        dst = kmem_cache_alloc(ops->kmem_cachep, GFP_ATOMIC);
        if (!dst)
                return NULL;

        dst_init(dst, ops, dev, initial_ref, initial_obsolete, flags);

        return dst;
}
EXPORT_SYMBOL(dst_alloc);

static void ___dst_free(struct dst_entry *dst)
{
        /* The first case (dev==NULL) is required, when
           protocol module is unloaded.
         */
        if (dst->dev == NULL || !(dst->dev->flags&IFF_UP)) {
                dst->input = dst_discard;
                dst->output = dst_discard_sk;
        }
        dst->obsolete = DST_OBSOLETE_DEAD;
}

void __dst_free(struct dst_entry *dst)
{
        spin_lock_bh(&dst_garbage.lock);
        ___dst_free(dst);
        dst->next = dst_garbage.list;
        dst_garbage.list = dst;
        if (dst_garbage.timer_inc > DST_GC_INC) {
                dst_garbage.timer_inc = DST_GC_INC;
                dst_garbage.timer_expires = DST_GC_MIN;
                mod_delayed_work(system_wq, &dst_gc_work,
                                 dst_garbage.timer_expires);
        }
        spin_unlock_bh(&dst_garbage.lock);
}
EXPORT_SYMBOL(__dst_free);

struct dst_entry *dst_destroy(struct dst_entry * dst)
{
        struct dst_entry *child;

        smp_rmb();

again:
        child = dst->child;

        if (!(dst->flags & DST_NOCOUNT))
                dst_entries_add(dst->ops, -1);

        if (dst->ops->destroy)
                dst->ops->destroy(dst);
        if (dst->dev)
                dev_put(dst->dev);

        lwtstate_put(dst->lwtstate);

        if (dst->flags & DST_METADATA)
                metadata_dst_free((struct metadata_dst *)dst);
        else
                kmem_cache_free(dst->ops->kmem_cachep, dst);

        dst = child;
        if (dst) {
                int nohash = dst->flags & DST_NOHASH;

                if (atomic_dec_and_test(&dst->__refcnt)) {
                        /* We were real parent of this dst, so kill child. */
                        if (nohash)
                                goto again;
                } else {
                        /* Child is still referenced, return it for freeing. */
                        if (nohash)
                                return dst;
                        /* Child is still in his hash table */
                }
        }
        return NULL;
}
EXPORT_SYMBOL(dst_destroy);

static void dst_destroy_rcu(struct rcu_head *head)
{
        struct dst_entry *dst = container_of(head, struct dst_entry, rcu_head);

        dst = dst_destroy(dst);
        if (dst)
                __dst_free(dst);
}

void dst_release(struct dst_entry *dst)
{
        if (dst) {
                int newrefcnt;
                unsigned short nocache = dst->flags & DST_NOCACHE;

                newrefcnt = atomic_dec_return(&dst->__refcnt);
                if (unlikely(newrefcnt < 0))
                        net_warn_ratelimited("%s: dst:%p refcnt:%d\n",
                                             __func__, dst, newrefcnt);
                if (!newrefcnt && unlikely(nocache))
                        call_rcu(&dst->rcu_head, dst_destroy_rcu);
        }
}
EXPORT_SYMBOL(dst_release);

u32 *dst_cow_metrics_generic(struct dst_entry *dst, unsigned long old)
{
        struct dst_metrics *p = kmalloc(sizeof(*p), GFP_ATOMIC);

        if (p) {
                struct dst_metrics *old_p = (struct dst_metrics *)__DST_METRICS_PTR(old);
                unsigned long prev, new;

                atomic_set(&p->refcnt, 1);
                memcpy(p->metrics, old_p->metrics, sizeof(p->metrics));

                new = (unsigned long) p;
                prev = cmpxchg(&dst->_metrics, old, new);

                if (prev != old) {
                        kfree(p);
                        p = (struct dst_metrics *)__DST_METRICS_PTR(prev);
                        if (prev & DST_METRICS_READ_ONLY)
                                p = NULL;
                } else if (prev & DST_METRICS_REFCOUNTED) {
                        if (atomic_dec_and_test(&old_p->refcnt))
                                kfree(old_p);
                }
        }
        BUILD_BUG_ON(offsetof(struct dst_metrics, metrics) != 0);
        return (u32 *)p;
}
EXPORT_SYMBOL(dst_cow_metrics_generic);

/* Caller asserts that dst_metrics_read_only(dst) is false.  */
void __dst_destroy_metrics_generic(struct dst_entry *dst, unsigned long old)
{
        unsigned long prev, new;

        new = ((unsigned long) &dst_default_metrics) | DST_METRICS_READ_ONLY;
        prev = cmpxchg(&dst->_metrics, old, new);
        if (prev == old)
                kfree(__DST_METRICS_PTR(old));
}
EXPORT_SYMBOL(__dst_destroy_metrics_generic);

static struct dst_ops md_dst_ops = {
        .family =               AF_UNSPEC,
};

static int dst_md_discard_sk(struct sock *sk, struct sk_buff *skb)
{
        WARN_ONCE(1, "Attempting to call output on metadata dst\n");
        kfree_skb(skb);
        return 0;
}

static int dst_md_discard(struct sk_buff *skb)
{
        WARN_ONCE(1, "Attempting to call input on metadata dst\n");
        kfree_skb(skb);
        return 0;
}

struct metadata_dst *metadata_dst_alloc(u8 optslen, enum metadata_type type,
                                        gfp_t flags)
{
        struct metadata_dst *md_dst;
        struct dst_entry *dst;

        md_dst = kmalloc(sizeof(*md_dst) + optslen, flags);
        if (!md_dst)
                return NULL;

        dst = &md_dst->dst;
        dst_init(dst, &md_dst_ops, NULL, 1, DST_OBSOLETE_NONE,
                 DST_METADATA | DST_NOCACHE | DST_NOCOUNT);

        dst->input = dst_md_discard;
        dst->output = dst_md_discard_sk;

        memset(dst + 1, 0, sizeof(*md_dst) + optslen - sizeof(*dst));
        md_dst->opts_len = optslen;
        md_dst->type = type;

        return md_dst;
}
EXPORT_SYMBOL_GPL(metadata_dst_alloc);

void metadata_dst_free(struct metadata_dst *md_dst)
{
#ifdef CONFIG_DST_CACHE
        if (md_dst->type == METADATA_IP_TUNNEL)
                dst_cache_destroy(&md_dst->u.tun_info.dst_cache);
#endif
        kfree(md_dst);
}

/* Dirty hack. We did it in 2.2 (in __dst_free),
 * we have _very_ good reasons not to repeat
 * this mistake in 2.3, but we have no choice
 * now. _It_ _is_ _explicit_ _deliberate_
 * _race_ _condition_.
 *
 * Commented and originally written by Alexey.
 */
static void dst_ifdown(struct dst_entry *dst, struct net_device *dev,
                       int unregister)
{
        if (dst->ops->ifdown)
                dst->ops->ifdown(dst, dev, unregister);

        if (dev != dst->dev)
                return;

        if (!unregister) {
                dst->input = dst_discard;
                dst->output = dst_discard_sk;
        } else {
                dst->dev = dev_net(dst->dev)->loopback_dev;
                dev_hold(dst->dev);
                dev_put(dev);
        }
}

static int dst_dev_event(struct notifier_block *this, unsigned long event,
                         void *ptr)
{
        struct net_device *dev = netdev_notifier_info_to_dev(ptr);
        struct dst_entry *dst, *last = NULL;

        switch (event) {
        case NETDEV_UNREGISTER_FINAL:
        case NETDEV_DOWN:
                mutex_lock(&dst_gc_mutex);
                for (dst = dst_busy_list; dst; dst = dst->next) {
                        last = dst;
                        dst_ifdown(dst, dev, event != NETDEV_DOWN);
                }

                spin_lock_bh(&dst_garbage.lock);
                dst = dst_garbage.list;
                dst_garbage.list = NULL;
                /* The code in dst_ifdown places a hold on the loopback device.
                 * If the gc entry processing is set to expire after a lengthy
                 * interval, this hold can cause netdev_wait_allrefs() to hang
                 * out and wait for a long time -- until the the loopback
                 * interface is released.  If we're really unlucky, it'll emit
                 * pr_emerg messages to console too.  Reset the interval here,
                 * so dst cleanups occur in a more timely fashion.
                 */
                if (dst_garbage.timer_inc > DST_GC_INC) {
                        dst_garbage.timer_inc = DST_GC_INC;
                        dst_garbage.timer_expires = DST_GC_MIN;
                        mod_delayed_work(system_wq, &dst_gc_work,
                                         dst_garbage.timer_expires);
                }
                spin_unlock_bh(&dst_garbage.lock);

                if (last)
                        last->next = dst;
                else
                        dst_busy_list = dst;
                for (; dst; dst = dst->next)
                        dst_ifdown(dst, dev, event != NETDEV_DOWN);
                mutex_unlock(&dst_gc_mutex);
                break;
        }
        return NOTIFY_DONE;
}

static struct notifier_block dst_dev_notifier = {
        .notifier_call  = dst_dev_event,
        .priority = -10, /* must be called after other network notifiers */
};

void __init dst_subsys_init(void)
{
        register_netdevice_notifier_rh(&dst_dev_notifier);
}