/*
 * 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>

#include <net/dst.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(struct sk_buff *skb)
{
        kfree_skb(skb);
        return 0;
}
EXPORT_SYMBOL(dst_discard);

const u32 dst_default_metrics[RTAX_MAX + 1] = {
        /* 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.
         */
        [RTAX_MAX] = 0xdeadbeef,
};


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->child = NULL;
        dst->dev = dev;
        if (dev)
                dev_hold(dev);
        dst->ops = ops;
        dst_init_metrics(dst, dst_default_metrics, true);
        dst->expires = 0UL;
        dst->path = dst;
#ifdef CONFIG_XFRM
        dst->xfrm = NULL;
#endif
        dst->input = dst_discard;
        dst->output = dst_discard;
        dst->error = 0;
        dst->obsolete = initial_obsolete;
        dst->header_len = 0;
        dst->trailer_len = 0;
#ifdef CONFIG_IP_ROUTE_CLASSID
        dst->tclassid = 0;
#endif
        atomic_set(&dst->__refcnt, initial_ref);
        dst->__use = 0;
        dst->lastuse = jiffies;
        dst->flags = flags;
        dst->pending_confirm = 0;
        dst->next = NULL;
        if (!(flags & DST_NOCOUNT))
                dst_entries_add(ops, 1);
        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->output = dst_discard;
        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);
        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);

void dst_release(struct dst_entry *dst)
{
        if (dst) {
                int newrefcnt;

                newrefcnt = atomic_dec_return(&dst->__refcnt);
                WARN_ON(newrefcnt < 0);
                if (unlikely(dst->flags & DST_NOCACHE) && !newrefcnt) {
                        dst = dst_destroy(dst);
                        if (dst)
                                __dst_free(dst);
                }
        }
}
EXPORT_SYMBOL(dst_release);

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

        if (p) {
                u32 *old_p = __DST_METRICS_PTR(old);
                unsigned long prev, new;

                memcpy(p, old_p, sizeof(u32) * RTAX_MAX);

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

                if (prev != old) {
                        kfree(p);
                        p = __DST_METRICS_PTR(prev);
                        if (prev & DST_METRICS_READ_ONLY)
                                p = NULL;
                }
        }
        return 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);

/**
 * skb_dst_set_noref - sets skb dst, without a reference
 * @skb: buffer
 * @dst: dst entry
 *
 * Sets skb dst, assuming a reference was not taken on dst
 * skb_dst_drop() should not dst_release() this dst
 */
void skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst)
{
        WARN_ON(!rcu_read_lock_held() && !rcu_read_lock_bh_held());
        /* If dst not in cache, we must take a reference, because
         * dst_release() will destroy dst as soon as its refcount becomes zero
         */
        if (unlikely(dst->flags & DST_NOCACHE)) {
                dst_hold(dst);
                skb_dst_set(skb, dst);
        } else {
                skb->_skb_refdst = (unsigned long)dst | SKB_DST_NOREF;
        }
}
EXPORT_SYMBOL(skb_dst_set_noref);

/* 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->output = dst_discard;
        } 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 = 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;
                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_init(void)
{
        register_netdevice_notifier(&dst_dev_notifier);
}