/*
 *	Linux INET6 implementation 
 *	Forwarding Information Database
 *
 *	Authors:
 *	Pedro Roque		<roque@di.fc.ul.pt>	
 *
 *	$Id: ip6_fib.c,v 1.1.1.1 2002/03/18 15:12:20 jharrell Exp $
 *
 *	This program is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU General Public License
 *      as published by the Free Software Foundation; either version
 *      2 of the License, or (at your option) any later version.
 */

#include <linux/config.h>
#include <linux/errno.h>
#include <linux/types.h>
#include <linux/net.h>
#include <linux/route.h>
#include <linux/netdevice.h>
#include <linux/in6.h>
#include <linux/init.h>

#ifdef 	CONFIG_PROC_FS
#include <linux/proc_fs.h>
#endif

#include <net/ipv6.h>
#include <net/ndisc.h>
#include <net/addrconf.h>

#include <net/ip6_fib.h>
#include <net/ip6_route.h>

#define RT6_DEBUG 2
#undef CONFIG_IPV6_SUBTREES

#if RT6_DEBUG >= 3
#define RT6_TRACE(x...) printk(KERN_DEBUG x)
#else
#define RT6_TRACE(x...) do { ; } while (0)
#endif

struct rt6_statistics	rt6_stats;

static kmem_cache_t * fib6_node_kmem;

enum fib_walk_state_t
{
#ifdef CONFIG_IPV6_SUBTREES
	FWS_S,
#endif
	FWS_L,
	FWS_R,
	FWS_C,
	FWS_U
};

struct fib6_cleaner_t
{
	struct fib6_walker_t w;
	int (*func)(struct rt6_info *, void *arg);
	void *arg;
};

rwlock_t fib6_walker_lock = RW_LOCK_UNLOCKED;


#ifdef CONFIG_IPV6_SUBTREES
#define FWS_INIT FWS_S
#define SUBTREE(fn) ((fn)->subtree)
#else
#define FWS_INIT FWS_L
#define SUBTREE(fn) NULL
#endif

static void fib6_prune_clones(struct fib6_node *fn, struct rt6_info *rt);
static struct fib6_node * fib6_repair_tree(struct fib6_node *fn);

/*
 *	A routing update causes an increase of the serial number on the
 *	afected subtree. This allows for cached routes to be asynchronously
 *	tested when modifications are made to the destination cache as a
 *	result of redirects, path MTU changes, etc.
 */

static __u32	rt_sernum	= 0;

static struct timer_list ip6_fib_timer = { function: fib6_run_gc };

static struct fib6_walker_t fib6_walker_list = {
	&fib6_walker_list, &fib6_walker_list, 
};

#define FOR_WALKERS(w) for ((w)=fib6_walker_list.next; (w) != &fib6_walker_list; (w)=(w)->next)

static __inline__ u32 fib6_new_sernum(void)
{
	u32 n = ++rt_sernum;
	if ((__s32)n <= 0)
		rt_sernum = n = 1;
	return n;
}

/*
 *	Auxiliary address test functions for the radix tree.
 *
 *	These assume a 32bit processor (although it will work on 
 *	64bit processors)
 */

/*
 *	compare "prefix length" bits of an address
 */

static __inline__ int addr_match(void *token1, void *token2, int prefixlen)
{
	__u32 *a1 = token1;
	__u32 *a2 = token2;
	int pdw;
	int pbi;

	pdw = prefixlen >> 5;	  /* num of whole __u32 in prefix */
	pbi = prefixlen &  0x1f;  /* num of bits in incomplete u32 in prefix */

	if (pdw)
		if (memcmp(a1, a2, pdw << 2))
			return 0;

	if (pbi) {
		__u32 mask;

		mask = htonl((0xffffffff) << (32 - pbi));

		if ((a1[pdw] ^ a2[pdw]) & mask)
			return 0;
	}

	return 1;
}

/*
 *	test bit
 */

static __inline__ int addr_bit_set(void *token, int fn_bit)
{
	__u32 *addr = token;

	return htonl(1 << ((~fn_bit)&0x1F)) & addr[fn_bit>>5];
}

/*
 *	find the first different bit between two addresses
 *	length of address must be a multiple of 32bits
 */

static __inline__ int addr_diff(void *token1, void *token2, int addrlen)
{
	__u32 *a1 = token1;
	__u32 *a2 = token2;
	int i;

	addrlen >>= 2;

	for (i = 0; i < addrlen; i++) {
		__u32 xb;

		xb = a1[i] ^ a2[i];

		if (xb) {
			int j = 31;

			xb = ntohl(xb);

			while ((xb & (1 << j)) == 0)
				j--;

			return (i * 32 + 31 - j);
		}
	}

	/*
	 *	we should *never* get to this point since that 
	 *	would mean the addrs are equal
	 *
	 *	However, we do get to it 8) And exacly, when
	 *	addresses are equal 8)
	 *
	 *	ip route add 1111::/128 via ...
	 *	ip route add 1111::/64 via ...
	 *	and we are here.
	 *
	 *	Ideally, this function should stop comparison
	 *	at prefix length. It does not, but it is still OK,
	 *	if returned value is greater than prefix length.
	 *					--ANK (980803)
	 */

	return addrlen<<5;
}

static __inline__ struct fib6_node * node_alloc(void)
{
	struct fib6_node *fn;

	if ((fn = kmem_cache_alloc(fib6_node_kmem, SLAB_ATOMIC)) != NULL)
		memset(fn, 0, sizeof(struct fib6_node));

	return fn;
}

static __inline__ void node_free(struct fib6_node * fn)
{
	kmem_cache_free(fib6_node_kmem, fn);
}

static __inline__ void rt6_release(struct rt6_info *rt)
{
	if (atomic_dec_and_test(&rt->rt6i_ref))
		dst_free(&rt->u.dst);
}


/*
 *	Routing Table
 *
 *	return the apropriate node for a routing tree "add" operation
 *	by either creating and inserting or by returning an existing
 *	node.
 */

static struct fib6_node * fib6_add_1(struct fib6_node *root, void *addr,
				     int addrlen, int plen,
				     int offset)
{
	struct fib6_node *fn, *in, *ln;
	struct fib6_node *pn = NULL;
	struct rt6key *key;
	int	bit;
       	int	dir = 0;
	__u32	sernum = fib6_new_sernum();

	RT6_TRACE("fib6_add_1\n");

	/* insert node in tree */

	fn = root;

	if (plen == 0)
		return fn;

	do {
		key = (struct rt6key *)((u8 *)fn->leaf + offset);

		/*
		 *	Prefix match
		 */
		if (plen < fn->fn_bit ||
		    !addr_match(&key->addr, addr, fn->fn_bit))
			goto insert_above;
		
		/*
		 *	Exact match ?
		 */
			 
		if (plen == fn->fn_bit) {
			/* clean up an intermediate node */
			if ((fn->fn_flags & RTN_RTINFO) == 0) {
				rt6_release(fn->leaf);
				fn->leaf = NULL;
			}
			
			fn->fn_sernum = sernum;
				
			return fn;
		}

		/*
		 *	We have more bits to go
		 */
			 
		/* Try to walk down on tree. */
		fn->fn_sernum = sernum;
		dir = addr_bit_set(addr, fn->fn_bit);
		pn = fn;
		fn = dir ? fn->right: fn->left;
	} while (fn);

	/*
	 *	We walked to the bottom of tree.
	 *	Create new leaf node without children.
	 */

	ln = node_alloc();

	if (ln == NULL)
		return NULL;
	ln->fn_bit = plen;
			
	ln->parent = pn;
	ln->fn_sernum = sernum;

	if (dir)
		pn->right = ln;
	else
		pn->left  = ln;

	return ln;


insert_above:
	/*
	 * split since we don't have a common prefix anymore or 
	 * we have a less significant route.
	 * we've to insert an intermediate node on the list
	 * this new node will point to the one we need to create
	 * and the current
	 */

	pn = fn->parent;

	/* find 1st bit in difference between the 2 addrs.

	   See comment in addr_diff: bit may be an invalid value,
	   but if it is >= plen, the value is ignored in any case.
	 */
	
	bit = addr_diff(addr, &key->addr, addrlen);

	/* 
	 *		(intermediate)[in]	
	 *	          /	   \
	 *	(new leaf node)[ln] (old node)[fn]
	 */
	if (plen > bit) {
		in = node_alloc();
		ln = node_alloc();
		
		if (in == NULL || ln == NULL) {
			if (in)
				node_free(in);
			if (ln)
				node_free(ln);
			return NULL;
		}

		/* 
		 * new intermediate node. 
		 * RTN_RTINFO will
		 * be off since that an address that chooses one of
		 * the branches would not match less specific routes
		 * in the other branch
		 */

		in->fn_bit = bit;

		in->parent = pn;
		in->leaf = fn->leaf;
		atomic_inc(&in->leaf->rt6i_ref);

		in->fn_sernum = sernum;

		/* update parent pointer */
		if (dir)
			pn->right = in;
		else
			pn->left  = in;

		ln->fn_bit = plen;

		ln->parent = in;
		fn->parent = in;

		ln->fn_sernum = sernum;

		if (addr_bit_set(addr, bit)) {
			in->right = ln;
			in->left  = fn;
		} else {
			in->left  = ln;
			in->right = fn;
		}
	} else { /* plen <= bit */

		/* 
		 *		(new leaf node)[ln]
		 *	          /	   \
		 *	     (old node)[fn] NULL
		 */

		ln = node_alloc();

		if (ln == NULL)
			return NULL;

		ln->fn_bit = plen;

		ln->parent = pn;

		ln->fn_sernum = sernum;
		
		if (dir)
			pn->right = ln;
		else
			pn->left  = ln;

		if (addr_bit_set(&key->addr, plen))
			ln->right = fn;
		else
			ln->left  = fn;

		fn->parent = ln;
	}
	return ln;
}

/*
 *	Insert routing information in a node.
 */

static int fib6_add_rt2node(struct fib6_node *fn, struct rt6_info *rt)
{
	struct rt6_info *iter = NULL;
	struct rt6_info **ins;

	ins = &fn->leaf;

	for (iter = fn->leaf; iter; iter=iter->u.next) {
		/*
		 *	Search for duplicates
		 */

		if (iter->rt6i_metric == rt->rt6i_metric) {
			/*
			 *	Same priority level
			 */

			if ((iter->rt6i_dev == rt->rt6i_dev) &&
			    (iter->rt6i_flowr == rt->rt6i_flowr) &&
			    (ipv6_addr_cmp(&iter->rt6i_gateway,
					   &rt->rt6i_gateway) == 0)) {
				if (!(iter->rt6i_flags&RTF_EXPIRES))
					return -EEXIST;
				iter->rt6i_expires = rt->rt6i_expires;
				if (!(rt->rt6i_flags&RTF_EXPIRES)) {
					iter->rt6i_flags &= ~RTF_EXPIRES;
					iter->rt6i_expires = 0;
				}
				return -EEXIST;
			}
		}

		if (iter->rt6i_metric > rt->rt6i_metric)
			break;

		ins = &iter->u.next;
	}

	/*
	 *	insert node
	 */

	rt->u.next = iter;
	*ins = rt;
	rt->rt6i_node = fn;
	atomic_inc(&rt->rt6i_ref);
	inet6_rt_notify(RTM_NEWROUTE, rt);
	rt6_stats.fib_rt_entries++;

	if ((fn->fn_flags & RTN_RTINFO) == 0) {
		rt6_stats.fib_route_nodes++;
		fn->fn_flags |= RTN_RTINFO;
	}

	return 0;
}

static __inline__ void fib6_start_gc(struct rt6_info *rt)
{
	if (ip6_fib_timer.expires == 0 &&
	    (rt->rt6i_flags & (RTF_EXPIRES|RTF_CACHE)))
		mod_timer(&ip6_fib_timer, jiffies + ip6_rt_gc_interval);
}

/*
 *	Add routing information to the routing tree.
 *	<destination addr>/<source addr>
 *	with source addr info in sub-trees
 */

int fib6_add(struct fib6_node *root, struct rt6_info *rt)
{
	struct fib6_node *fn;
	int err = -ENOMEM;

	fn = fib6_add_1(root, &rt->rt6i_dst.addr, sizeof(struct in6_addr),
			rt->rt6i_dst.plen, (u8*) &rt->rt6i_dst - (u8*) rt);

	if (fn == NULL)
		goto out;

#ifdef CONFIG_IPV6_SUBTREES
	if (rt->rt6i_src.plen) {
		struct fib6_node *sn;

		if (fn->subtree == NULL) {
			struct fib6_node *sfn;

			/*
			 * Create subtree.
			 *
			 *		fn[main tree]
			 *		|
			 *		sfn[subtree root]
			 *		   \
			 *		    sn[new leaf node]
			 */

			/* Create subtree root node */
			sfn = node_alloc();
			if (sfn == NULL)
				goto st_failure;

			sfn->leaf = &ip6_null_entry;
			atomic_inc(&ip6_null_entry.rt6i_ref);
			sfn->fn_flags = RTN_ROOT;
			sfn->fn_sernum = fib6_new_sernum();

			/* Now add the first leaf node to new subtree */

			sn = fib6_add_1(sfn, &rt->rt6i_src.addr,
					sizeof(struct in6_addr), rt->rt6i_src.plen,
					(u8*) &rt->rt6i_src - (u8*) rt);

			if (sn == NULL) {
				/* If it is failed, discard just allocated
				   root, and then (in st_failure) stale node
				   in main tree.
				 */
				node_free(sfn);
				goto st_failure;
			}

			/* Now link new subtree to main tree */
			sfn->parent = fn;
			fn->subtree = sfn;
			if (fn->leaf == NULL) {
				fn->leaf = rt;
				atomic_inc(&rt->rt6i_ref);
			}
		} else {
			sn = fib6_add_1(fn->subtree, &rt->rt6i_src.addr,
					sizeof(struct in6_addr), rt->rt6i_src.plen,
					(u8*) &rt->rt6i_src - (u8*) rt);

			if (sn == NULL)
				goto st_failure;
		}

		fn = sn;
	}
#endif

	err = fib6_add_rt2node(fn, rt);

	if (err == 0) {
		fib6_start_gc(rt);
		if (!(rt->rt6i_flags&RTF_CACHE))
			fib6_prune_clones(fn, rt);
	}

out:
	if (err)
		dst_free(&rt->u.dst);
	return err;

#ifdef CONFIG_IPV6_SUBTREES
	/* Subtree creation failed, probably main tree node
	   is orphan. If it is, shot it.
	 */
st_failure:
	if (fn && !(fn->fn_flags&RTN_RTINFO|RTN_ROOT))
		fib_repair_tree(fn);
	dst_free(&rt->u.dst);
	return err;
#endif
}

/*
 *	Routing tree lookup
 *
 */

struct lookup_args {
	int		offset;		/* key offset on rt6_info	*/
	struct in6_addr	*addr;		/* search key			*/
};

static struct fib6_node * fib6_lookup_1(struct fib6_node *root,
					struct lookup_args *args)
{
	struct fib6_node *fn;
	int dir;

	/*
	 *	Descend on a tree
	 */

	fn = root;

	for (;;) {
		struct fib6_node *next;

		dir = addr_bit_set(args->addr, fn->fn_bit);

		next = dir ? fn->right : fn->left;

		if (next) {
			fn = next;
			continue;
		}

		break;
	}

	while ((fn->fn_flags & RTN_ROOT) == 0) {
#ifdef CONFIG_IPV6_SUBTREES
		if (fn->subtree) {
			struct fib6_node *st;
			struct lookup_args *narg;

			narg = args + 1;

			if (narg->addr) {
				st = fib6_lookup_1(fn->subtree, narg);

				if (st && !(st->fn_flags & RTN_ROOT))
					return st;
			}
		}
#endif

		if (fn->fn_flags & RTN_RTINFO) {
			struct rt6key *key;

			key = (struct rt6key *) ((u8 *) fn->leaf +
						 args->offset);

			if (addr_match(&key->addr, args->addr, key->plen))
				return fn;
		}

		fn = fn->parent;
	}

	return NULL;
}

struct fib6_node * fib6_lookup(struct fib6_node *root, struct in6_addr *daddr,
			       struct in6_addr *saddr)
{
	struct lookup_args args[2];
	struct rt6_info *rt = NULL;
	struct fib6_node *fn;

	args[0].offset = (u8*) &rt->rt6i_dst - (u8*) rt;
	args[0].addr = daddr;

#ifdef CONFIG_IPV6_SUBTREES
	args[1].offset = (u8*) &rt->rt6i_src - (u8*) rt;
	args[1].addr = saddr;
#endif

	fn = fib6_lookup_1(root, args);

	if (fn == NULL)
		fn = root;

	return fn;
}

/*
 *	Get node with sepciafied destination prefix (and source prefix,
 *	if subtrees are used)
 */


static struct fib6_node * fib6_locate_1(struct fib6_node *root,
					struct in6_addr *addr,
					int plen, int offset)
{
	struct fib6_node *fn;

	for (fn = root; fn ; ) {
		struct rt6key *key = (struct rt6key *)((u8 *)fn->leaf + offset);

		/*
		 *	Prefix match
		 */
		if (plen < fn->fn_bit ||
		    !addr_match(&key->addr, addr, fn->fn_bit))
			return NULL;

		if (plen == fn->fn_bit)
			return fn;

		/*
		 *	We have more bits to go
		 */
		if (addr_bit_set(addr, fn->fn_bit))
			fn = fn->right;
		else
			fn = fn->left;
	}
	return NULL;
}

struct fib6_node * fib6_locate(struct fib6_node *root,
			       struct in6_addr *daddr, int dst_len,
			       struct in6_addr *saddr, int src_len)
{
	struct rt6_info *rt = NULL;
	struct fib6_node *fn;

	fn = fib6_locate_1(root, daddr, dst_len,
			   (u8*) &rt->rt6i_dst - (u8*) rt);

#ifdef CONFIG_IPV6_SUBTREES
	if (src_len) {
		BUG_TRAP(saddr!=NULL);
		if (fn == NULL)
			fn = fn->subtree;
		if (fn)
			fn = fib6_locate_1(fn, saddr, src_len,
					   (u8*) &rt->rt6i_src - (u8*) rt);
	}
#endif

	if (fn && fn->fn_flags&RTN_RTINFO)
		return fn;

	return NULL;
}


/*
 *	Deletion
 *
 */

static struct rt6_info * fib6_find_prefix(struct fib6_node *fn)
{
	if (fn->fn_flags&RTN_ROOT)
		return &ip6_null_entry;

	while(fn) {
		if(fn->left)
			return fn->left->leaf;

		if(fn->right)
			return fn->right->leaf;

		fn = SUBTREE(fn);
	}
	return NULL;
}

/*
 *	Called to trim the tree of intermediate nodes when possible. "fn"
 *	is the node we want to try and remove.
 */

static struct fib6_node * fib6_repair_tree(struct fib6_node *fn)
{
	int children;
	int nstate;
	struct fib6_node *child, *pn;
	struct fib6_walker_t *w;
	int iter = 0;

	for (;;) {
		RT6_TRACE("fixing tree: plen=%d iter=%d\n", fn->fn_bit, iter);
		iter++;

		BUG_TRAP(!(fn->fn_flags&RTN_RTINFO));
		BUG_TRAP(!(fn->fn_flags&RTN_TL_ROOT));
		BUG_TRAP(fn->leaf==NULL);

		children = 0;
		child = NULL;
		if (fn->right) child = fn->right, children |= 1;
		if (fn->left) child = fn->left, children |= 2;

		if (children == 3 || SUBTREE(fn) 
#ifdef CONFIG_IPV6_SUBTREES
		    /* Subtree root (i.e. fn) may have one child */
		    || (children && fn->fn_flags&RTN_ROOT)
#endif
		    ) {
			fn->leaf = fib6_find_prefix(fn);
#if RT6_DEBUG >= 2
			if (fn->leaf==NULL) {
				BUG_TRAP(fn->leaf);
				fn->leaf = &ip6_null_entry;
			}
#endif
			atomic_inc(&fn->leaf->rt6i_ref);
			return fn->parent;
		}

		pn = fn->parent;
#ifdef CONFIG_IPV6_SUBTREES
		if (SUBTREE(pn) == fn) {
			BUG_TRAP(fn->fn_flags&RTN_ROOT);
			SUBTREE(pn) = NULL;
			nstate = FWS_L;
		} else {
			BUG_TRAP(!(fn->fn_flags&RTN_ROOT));
#endif
			if (pn->right == fn) pn->right = child;
			else if (pn->left == fn) pn->left = child;
#if RT6_DEBUG >= 2
			else BUG_TRAP(0);
#endif
			if (child)
				child->parent = pn;
			nstate = FWS_R;
#ifdef CONFIG_IPV6_SUBTREES
		}
#endif

		read_lock(&fib6_walker_lock);
		FOR_WALKERS(w) {
			if (child == NULL) {
				if (w->root == fn) {
					w->root = w->node = NULL;
					RT6_TRACE("W %p adjusted by delroot 1\n", w);
				} else if (w->node == fn) {
					RT6_TRACE("W %p adjusted by delnode 1, s=%d/%d\n", w, w->state, nstate);
					w->node = pn;
					w->state = nstate;
				}
			} else {
				if (w->root == fn) {
					w->root = child;
					RT6_TRACE("W %p adjusted by delroot 2\n", w);
				}
				if (w->node == fn) {
					w->node = child;
					if (children&2) {
						RT6_TRACE("W %p adjusted by delnode 2, s=%d\n", w, w->state);
						w->state = w->state>=FWS_R ? FWS_U : FWS_INIT;
					} else {
						RT6_TRACE("W %p adjusted by delnode 2, s=%d\n", w, w->state);
						w->state = w->state>=FWS_C ? FWS_U : FWS_INIT;
					}
				}
			}
		}
		read_unlock(&fib6_walker_lock);

		node_free(fn);
		if (pn->fn_flags&RTN_RTINFO || SUBTREE(pn))
			return pn;

		rt6_release(pn->leaf);
		pn->leaf = NULL;
		fn = pn;
	}
}

static void fib6_del_route(struct fib6_node *fn, struct rt6_info **rtp)
{
	struct fib6_walker_t *w;
	struct rt6_info *rt = *rtp;

	RT6_TRACE("fib6_del_route\n");

	/* Unlink it */
	*rtp = rt->u.next;
	rt->rt6i_node = NULL;
	rt6_stats.fib_rt_entries--;

	/* Adjust walkers */
	read_lock(&fib6_walker_lock);
	FOR_WALKERS(w) {
		if (w->state == FWS_C && w->leaf == rt) {
			RT6_TRACE("walker %p adjusted by delroute\n", w);
			w->leaf = rt->u.next;
			if (w->leaf == NULL)
				w->state = FWS_U;
		}
	}
	read_unlock(&fib6_walker_lock);

	rt->u.next = NULL;

	/* If it was last route, expunge its radix tree node */
	if (fn->leaf == NULL) {
		fn->fn_flags &= ~RTN_RTINFO;
		rt6_stats.fib_route_nodes--;
		fn = fib6_repair_tree(fn);
	}

	if (atomic_read(&rt->rt6i_ref) != 1) {
		/* This route is used as dummy address holder in some split
		 * nodes. It is not leaked, but it still holds other resources,
		 * which must be released in time. So, scan ascendant nodes
		 * and replace dummy references to this route with references
		 * to still alive ones.
		 */
		while (fn) {
			if (!(fn->fn_flags&RTN_RTINFO) && fn->leaf == rt) {
				fn->leaf = fib6_find_prefix(fn);
				atomic_inc(&fn->leaf->rt6i_ref);
				rt6_release(rt);
			}
			fn = fn->parent;
		}
		/* No more references are possiible at this point. */
		if (atomic_read(&rt->rt6i_ref) != 1) BUG();
	}

	inet6_rt_notify(RTM_DELROUTE, rt);
	rt6_release(rt);
}

int fib6_del(struct rt6_info *rt)
{
	struct fib6_node *fn = rt->rt6i_node;
	struct rt6_info **rtp;

#if RT6_DEBUG >= 2
	if (rt->u.dst.obsolete>0) {
		BUG_TRAP(fn==NULL || rt->u.dst.obsolete<=0);
		return -ENOENT;
	}
#endif
	if (fn == NULL || rt == &ip6_null_entry)
		return -ENOENT;

	BUG_TRAP(fn->fn_flags&RTN_RTINFO);

	if (!(rt->rt6i_flags&RTF_CACHE))
		fib6_prune_clones(fn, rt);

	/*
	 *	Walk the leaf entries looking for ourself
	 */

	for (rtp = &fn->leaf; *rtp; rtp = &(*rtp)->u.next) {
		if (*rtp == rt) {
			fib6_del_route(fn, rtp);
			return 0;
		}
	}
	return -ENOENT;
}

/*
 *	Tree transversal function.
 *
 *	Certainly, it is not interrupt safe.
 *	However, it is internally reenterable wrt itself and fib6_add/fib6_del.
 *	It means, that we can modify tree during walking
 *	and use this function for garbage collection, clone pruning,
 *	cleaning tree when a device goes down etc. etc.	
 *
 *	It guarantees that every node will be traversed,
 *	and that it will be traversed only once.
 *
 *	Callback function w->func may return:
 *	0 -> continue walking.
 *	positive value -> walking is suspended (used by tree dumps,
 *	and probably by gc, if it will be split to several slices)
 *	negative value -> terminate walking.
 *
 *	The function itself returns:
 *	0   -> walk is complete.
 *	>0  -> walk is incomplete (i.e. suspended)
 *	<0  -> walk is terminated by an error.
 */

int fib6_walk_continue(struct fib6_walker_t *w)
{
	struct fib6_node *fn, *pn;

	for (;;) {
		fn = w->node;
		if (fn == NULL)
			return 0;

		if (w->prune && fn != w->root &&
		    fn->fn_flags&RTN_RTINFO && w->state < FWS_C) {
			w->state = FWS_C;
			w->leaf = fn->leaf;
		}
		switch (w->state) {
#ifdef CONFIG_IPV6_SUBTREES
		case FWS_S:
			if (SUBTREE(fn)) {
				w->node = SUBTREE(fn);
				continue;
			}
			w->state = FWS_L;
#endif	
		case FWS_L:
			if (fn->left) {
				w->node = fn->left;
				w->state = FWS_INIT;
				continue;
			}
			w->state = FWS_R;
		case FWS_R:
			if (fn->right) {
				w->node = fn->right;
				w->state = FWS_INIT;
				continue;
			}
			w->state = FWS_C;
			w->leaf = fn->leaf;
		case FWS_C:
			if (w->leaf && fn->fn_flags&RTN_RTINFO) {
				int err = w->func(w);
				if (err)
					return err;
				continue;
			}
			w->state = FWS_U;
		case FWS_U:
			if (fn == w->root)
				return 0;
			pn = fn->parent;
			w->node = pn;
#ifdef CONFIG_IPV6_SUBTREES
			if (SUBTREE(pn) == fn) {
				BUG_TRAP(fn->fn_flags&RTN_ROOT);
				w->state = FWS_L;
				continue;
			}
#endif
			if (pn->left == fn) {
				w->state = FWS_R;
				continue;
			}
			if (pn->right == fn) {
				w->state = FWS_C;
				w->leaf = w->node->leaf;
				continue;
			}
#if RT6_DEBUG >= 2
			BUG_TRAP(0);
#endif
		}
	}
}

int fib6_walk(struct fib6_walker_t *w)
{
	int res;

	w->state = FWS_INIT;
	w->node = w->root;

	fib6_walker_link(w);
	res = fib6_walk_continue(w);
	if (res <= 0)
		fib6_walker_unlink(w);
	return res;
}

static int fib6_clean_node(struct fib6_walker_t *w)
{
	int res;
	struct rt6_info *rt;
	struct fib6_cleaner_t *c = (struct fib6_cleaner_t*)w;

	for (rt = w->leaf; rt; rt = rt->u.next) {
		res = c->func(rt, c->arg);
		if (res < 0) {
			w->leaf = rt;
			res = fib6_del(rt);
			if (res) {
#if RT6_DEBUG >= 2
				printk(KERN_DEBUG "fib6_clean_node: del failed: rt=%p@%p err=%d\n", rt, rt->rt6i_node, res);
#endif
				continue;
			}
			return 0;
		}
		BUG_TRAP(res==0);
	}
	w->leaf = rt;
	return 0;
}

/*
 *	Convenient frontend to tree walker.
 *	
 *	func is called on each route.
 *		It may return -1 -> delete this route.
 *		              0  -> continue walking
 *
 *	prune==1 -> only immediate children of node (certainly,
 *	ignoring pure split nodes) will be scanned.
 */

void fib6_clean_tree(struct fib6_node *root,
		     int (*func)(struct rt6_info *, void *arg),
		     int prune, void *arg)
{
	struct fib6_cleaner_t c;

	c.w.root = root;
	c.w.func = fib6_clean_node;
	c.w.prune = prune;
	c.func = func;
	c.arg = arg;

	fib6_walk(&c.w);
}

static int fib6_prune_clone(struct rt6_info *rt, void *arg)
{
	if (rt->rt6i_flags & RTF_CACHE) {
		RT6_TRACE("pruning clone %p\n", rt);
		return -1;
	}

	return 0;
}

static void fib6_prune_clones(struct fib6_node *fn, struct rt6_info *rt)
{
	fib6_clean_tree(fn, fib6_prune_clone, 1, rt);
}

/*
 *	Garbage collection
 */

static struct fib6_gc_args
{
	int			timeout;
	int			more;
} gc_args;

static int fib6_age(struct rt6_info *rt, void *arg)
{
	unsigned long now = jiffies;

	/* Age clones. Note, that clones are aged out
	   only if they are not in use now.
	 */

	if (rt->rt6i_flags & RTF_CACHE) {
		if (atomic_read(&rt->u.dst.__refcnt) == 0 &&
		    (long)(now - rt->u.dst.lastuse) >= gc_args.timeout) {
			RT6_TRACE("aging clone %p\n", rt);
			return -1;
		}
		gc_args.more++;
	}

	/*
	 *	check addrconf expiration here.
	 *	They are expired even if they are in use.
	 */

	if (rt->rt6i_flags&RTF_EXPIRES && rt->rt6i_expires) {
		if ((long)(now - rt->rt6i_expires) > 0) {
			RT6_TRACE("expiring %p\n", rt);
			return -1;
		}
		gc_args.more++;
	}

	return 0;
}

static spinlock_t fib6_gc_lock = SPIN_LOCK_UNLOCKED;

void fib6_run_gc(unsigned long dummy)
{
	if (dummy != ~0UL) {
		spin_lock_bh(&fib6_gc_lock);
		gc_args.timeout = (int)dummy;
	} else {
		local_bh_disable();
		if (!spin_trylock(&fib6_gc_lock)) {
			mod_timer(&ip6_fib_timer, jiffies + HZ);
			local_bh_enable();
			return;
		}
		gc_args.timeout = ip6_rt_gc_interval;
	}
	gc_args.more = 0;


	write_lock_bh(&rt6_lock);
	fib6_clean_tree(&ip6_routing_table, fib6_age, 0, NULL);
	write_unlock_bh(&rt6_lock);

	if (gc_args.more)
		mod_timer(&ip6_fib_timer, jiffies + ip6_rt_gc_interval);
	else {
		del_timer(&ip6_fib_timer);
		ip6_fib_timer.expires = 0;
	}
	spin_unlock_bh(&fib6_gc_lock);
}

void __init fib6_init(void)
{
	if (!fib6_node_kmem)
		fib6_node_kmem = kmem_cache_create("fib6_nodes",
						   sizeof(struct fib6_node),
						   0, SLAB_HWCACHE_ALIGN,
						   NULL, NULL);
}

#ifdef MODULE
void fib6_gc_cleanup(void)
{
	del_timer(&ip6_fib_timer);
}
#endif


