/*
   * 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;

  	dst->from = NULL;

  #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

   * @force: if force is set, use noref version even for DST_NOCACHE entries

   *
   * 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, bool force)

  {
  	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) && !force)) {

  		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);
  }