/*
 * 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/netdevice.h>
#include <linux/skbuff.h>
#include <linux/string.h>
#include <linux/types.h>
#include <net/net_namespace.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.
 */
#if RT_CACHE_DEBUG >= 2
static atomic_t                  dst_total = ATOMIC_INIT(0);
#endif

/*
 * 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;
#if RT_CACHE_DEBUG >= 2
        ktime_t time_start = ktime_get();
        struct timespec elapsed;
#endif

        mutex_lock(&dst_gc_mutex);
        next = dst_busy_list;

loop:
        while ((dst = next) != NULL) {
                next = dst->next;
                prefetch(&next->next);
                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 > 1)
                                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);
#if RT_CACHE_DEBUG >= 2
        elapsed = ktime_to_timespec(ktime_sub(ktime_get(), time_start));
        printk(KERN_DEBUG "dst_total: %d delayed: %d work_perf: %d"
                " expires: %lu elapsed: %lu us\n",
                atomic_read(&dst_total), delayed, work_performed,
                expires,
                elapsed.tv_sec * USEC_PER_SEC + elapsed.tv_nsec / NSEC_PER_USEC);
#endif
}

int dst_discard(struct sk_buff *skb)
{
        kfree_skb(skb);
        return 0;
}
EXPORT_SYMBOL(dst_discard);

void * dst_alloc(struct dst_ops * ops)
{
        struct dst_entry * dst;

        if (ops->gc && atomic_read(&ops->entries) > ops->gc_thresh) {
                if (ops->gc(ops))
                        return NULL;
        }
        dst = kmem_cache_zalloc(ops->kmem_cachep, GFP_ATOMIC);
        if (!dst)
                return NULL;
        atomic_set(&dst->__refcnt, 0);
        dst->ops = ops;
        dst->lastuse = jiffies;
        dst->path = dst;
        dst->input = dst->output = dst_discard;
#if RT_CACHE_DEBUG >= 2
        atomic_inc(&dst_total);
#endif
        atomic_inc(&ops->entries);
        return dst;
}

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 = 2;
}

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;
                cancel_delayed_work(&dst_gc_work);
                schedule_delayed_work(&dst_gc_work, dst_garbage.timer_expires);
        }
        spin_unlock_bh(&dst_garbage.lock);
}

struct dst_entry *dst_destroy(struct dst_entry * dst)
{
        struct dst_entry *child;
        struct neighbour *neigh;
        struct hh_cache *hh;

        smp_rmb();

again:
        neigh = dst->neighbour;
        hh = dst->hh;
        child = dst->child;

        dst->hh = NULL;
        if (hh && atomic_dec_and_test(&hh->hh_refcnt))
                kfree(hh);

        if (neigh) {
                dst->neighbour = NULL;
                neigh_release(neigh);
        }

        atomic_dec(&dst->ops->entries);

        if (dst->ops->destroy)
                dst->ops->destroy(dst);
        if (dst->dev)
                dev_put(dst->dev);
#if RT_CACHE_DEBUG >= 2
        atomic_dec(&dst_total);
#endif
        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;
}

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

                smp_mb__before_atomic_dec();
               newrefcnt = atomic_dec_return(&dst->__refcnt);
               WARN_ON(newrefcnt < 0);
        }
}
EXPORT_SYMBOL(dst_release);

/* 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 inline 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);
                if (dst->neighbour && dst->neighbour->dev == dev) {
                        dst->neighbour->dev = dst->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:
        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,
};

void __init dst_init(void)
{
        register_netdevice_notifier(&dst_dev_notifier);
}

EXPORT_SYMBOL(__dst_free);
EXPORT_SYMBOL(dst_alloc);
EXPORT_SYMBOL(dst_destroy);