/*

 * 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) {

		smp_mb__before_atomic_dec();

	}

}

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);