fib_trie.c

/*
 *   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.
 *
 *   Robert Olsson <robert.olsson@its.uu.se> Uppsala Universitet
 *     & Swedish University of Agricultural Sciences.
 *
 *   Jens Laas <jens.laas@data.slu.se> Swedish University of
 *     Agricultural Sciences.
 *
 *   Hans Liss <hans.liss@its.uu.se>  Uppsala Universitet
 *
 * This work is based on the LPC-trie which is originally described in:
 *
 * An experimental study of compression methods for dynamic tries
 * Stefan Nilsson and Matti Tikkanen. Algorithmica, 33(1):19-33, 2002.
 * http://www.csc.kth.se/~snilsson/software/dyntrie2/
 *
 *
 * IP-address lookup using LC-tries. Stefan Nilsson and Gunnar Karlsson
 * IEEE Journal on Selected Areas in Communications, 17(6):1083-1092, June 1999
 *
 *
 * Code from fib_hash has been reused which includes the following header:
 *
 *
 * INET		An implementation of the TCP/IP protocol suite for the LINUX
 *		operating system.  INET is implemented using the  BSD Socket
 *		interface as the means of communication with the user level.
 *
 *		IPv4 FIB: lookup engine and maintenance routines.
 *
 *
 * Authors:	Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
 *
 *		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.
 *
 * Substantial contributions to this work comes from:
 *
 *		David S. Miller, <davem@davemloft.net>
 *		Stephen Hemminger <shemminger@osdl.org>
 *		Paul E. McKenney <paulmck@us.ibm.com>
 *		Patrick McHardy <kaber@trash.net>
 */

#define VERSION "0.409"

#include <linux/cache.h>
#include <linux/uaccess.h>
#include <linux/bitops.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/string.h>
#include <linux/socket.h>
#include <linux/sockios.h>
#include <linux/errno.h>
#include <linux/in.h>
#include <linux/inet.h>
#include <linux/inetdevice.h>
#include <linux/netdevice.h>
#include <linux/if_arp.h>
#include <linux/proc_fs.h>
#include <linux/rcupdate.h>
#include <linux/skbuff.h>
#include <linux/netlink.h>
#include <linux/init.h>
#include <linux/list.h>
#include <linux/slab.h>
#include <linux/export.h>
#include <linux/vmalloc.h>
#include <linux/notifier.h>
#include <net/net_namespace.h>
#include <net/ip.h>
#include <net/protocol.h>
#include <net/route.h>
#include <net/tcp.h>
#include <net/sock.h>
#include <net/ip_fib.h>
#include <net/fib_notifier.h>
#include <trace/events/fib.h>
#include "fib_lookup.h"

static int call_fib_entry_notifier(struct notifier_block *nb, struct net *net,
				   enum fib_event_type event_type, u32 dst,
				   int dst_len, struct fib_alias *fa)
{
	struct fib_entry_notifier_info info = {
		.dst = dst,
		.dst_len = dst_len,
		.fi = fa->fa_info,
		.tos = fa->fa_tos,
		.type = fa->fa_type,
		.tb_id = fa->tb_id,
	};
	return call_fib4_notifier(nb, net, event_type, &info.info);
}

static int call_fib_entry_notifiers(struct net *net,
				    enum fib_event_type event_type, u32 dst,
				    int dst_len, struct fib_alias *fa,
				    struct netlink_ext_ack *extack)
{
	struct fib_entry_notifier_info info = {
		.info.extack = extack,
		.dst = dst,
		.dst_len = dst_len,
		.fi = fa->fa_info,
		.tos = fa->fa_tos,
		.type = fa->fa_type,
		.tb_id = fa->tb_id,
	};
	return call_fib4_notifiers(net, event_type, &info.info);
}

#define MAX_STAT_DEPTH 32

#define KEYLENGTH	(8*sizeof(t_key))
#define KEY_MAX		((t_key)~0)

typedef unsigned int t_key;

#define IS_TRIE(n)	((n)->pos >= KEYLENGTH)
#define IS_TNODE(n)	((n)->bits)
#define IS_LEAF(n)	(!(n)->bits)

struct key_vector {
	t_key key;
	unsigned char pos;		/* 2log(KEYLENGTH) bits needed */
	unsigned char bits;		/* 2log(KEYLENGTH) bits needed */
	unsigned char slen;
	union {
		/* This list pointer if valid if (pos | bits) == 0 (LEAF) */
		struct hlist_head leaf;
		/* This array is valid if (pos | bits) > 0 (TNODE) */
		struct key_vector __rcu *tnode[0];
	};
};

struct tnode {
	struct rcu_head rcu;
	t_key empty_children;		/* KEYLENGTH bits needed */
	t_key full_children;		/* KEYLENGTH bits needed */
	struct key_vector __rcu *parent;
	struct key_vector kv[1];
#define tn_bits kv[0].bits
};

#define TNODE_SIZE(n)	offsetof(struct tnode, kv[0].tnode[n])
#define LEAF_SIZE	TNODE_SIZE(1)

#ifdef CONFIG_IP_FIB_TRIE_STATS
struct trie_use_stats {
	unsigned int gets;
	unsigned int backtrack;
	unsigned int semantic_match_passed;
	unsigned int semantic_match_miss;
	unsigned int null_node_hit;
	unsigned int resize_node_skipped;
};
#endif

struct trie_stat {
	unsigned int totdepth;
	unsigned int maxdepth;
	unsigned int tnodes;
	unsigned int leaves;
	unsigned int nullpointers;
	unsigned int prefixes;
	unsigned int nodesizes[MAX_STAT_DEPTH];
};

struct trie {
	struct key_vector kv[1];
#ifdef CONFIG_IP_FIB_TRIE_STATS
	struct trie_use_stats __percpu *stats;
#endif
};

static struct key_vector *resize(struct trie *t, struct key_vector *tn);
static size_t tnode_free_size;

/*
 * synchronize_rcu after call_rcu for that many pages; it should be especially
 * useful before resizing the root node with PREEMPT_NONE configs; the value was
 * obtained experimentally, aiming to avoid visible slowdown.
 */
static const int sync_pages = 128;

static struct kmem_cache *fn_alias_kmem __ro_after_init;
static struct kmem_cache *trie_leaf_kmem __ro_after_init;

static inline struct tnode *tn_info(struct key_vector *kv)
{
	return container_of(kv, struct tnode, kv[0]);
}

/* caller must hold RTNL */
#define node_parent(tn) rtnl_dereference(tn_info(tn)->parent)
#define get_child(tn, i) rtnl_dereference((tn)->tnode[i])

/* caller must hold RCU read lock or RTNL */
#define node_parent_rcu(tn) rcu_dereference_rtnl(tn_info(tn)->parent)
#define get_child_rcu(tn, i) rcu_dereference_rtnl((tn)->tnode[i])

/* wrapper for rcu_assign_pointer */
static inline void node_set_parent(struct key_vector *n, struct key_vector *tp)
{
	if (n)
		rcu_assign_pointer(tn_info(n)->parent, tp);
}

#define NODE_INIT_PARENT(n, p) RCU_INIT_POINTER(tn_info(n)->parent, p)

/* This provides us with the number of children in this node, in the case of a
 * leaf this will return 0 meaning none of the children are accessible.
 */
static inline unsigned long child_length(const struct key_vector *tn)
{
	return (1ul << tn->bits) & ~(1ul);
}

#define get_cindex(key, kv) (((key) ^ (kv)->key) >> (kv)->pos)

static inline unsigned long get_index(t_key key, struct key_vector *kv)
{
	unsigned long index = key ^ kv->key;

	if ((BITS_PER_LONG <= KEYLENGTH) && (KEYLENGTH == kv->pos))
		return 0;

	return index >> kv->pos;
}

/* To understand this stuff, an understanding of keys and all their bits is
 * necessary. Every node in the trie has a key associated with it, but not
 * all of the bits in that key are significant.
 *
 * Consider a node 'n' and its parent 'tp'.
 *
 * If n is a leaf, every bit in its key is significant. Its presence is
 * necessitated by path compression, since during a tree traversal (when
 * searching for a leaf - unless we are doing an insertion) we will completely
 * ignore all skipped bits we encounter. Thus we need to verify, at the end of
 * a potentially successful search, that we have indeed been walking the
 * correct key path.
 *
 * Note that we can never "miss" the correct key in the tree if present by
 * following the wrong path. Path compression ensures that segments of the key
 * that are the same for all keys with a given prefix are skipped, but the
 * skipped part *is* identical for each node in the subtrie below the skipped
 * bit! trie_insert() in this implementation takes care of that.
 *
 * if n is an internal node - a 'tnode' here, the various parts of its key
 * have many different meanings.
 *
 * Example:
 * _________________________________________________________________
 * | i | i | i | i | i | i | i | N | N | N | S | S | S | S | S | C |
 * -----------------------------------------------------------------
 *  31  30  29  28  27  26  25  24  23  22  21  20  19  18  17  16
 *
 * _________________________________________________________________
 * | C | C | C | u | u | u | u | u | u | u | u | u | u | u | u | u |
 * -----------------------------------------------------------------
 *  15  14  13  12  11  10   9   8   7   6   5   4   3   2   1   0
 *
 * tp->pos = 22
 * tp->bits = 3
 * n->pos = 13
 * n->bits = 4
 *
 * First, let's just ignore the bits that come before the parent tp, that is
 * the bits from (tp->pos + tp->bits) to 31. They are *known* but at this
 * point we do not use them for anything.
 *
 * The bits from (tp->pos) to (tp->pos + tp->bits - 1) - "N", above - are the
 * index into the parent's child array. That is, they will be used to find
 * 'n' among tp's children.
 *
 * The bits from (n->pos + n->bits) to (tp->pos - 1) - "S" - are skipped bits
 * for the node n.
 *
 * All the bits we have seen so far are significant to the node n. The rest
 * of the bits are really not needed or indeed known in n->key.
 *
 * The bits from (n->pos) to (n->pos + n->bits - 1) - "C" - are the index into
 * n's child array, and will of course be different for each child.
 *
 * The rest of the bits, from 0 to (n->pos -1) - "u" - are completely unknown
 * at this point.
 */

static const int halve_threshold = 25;
static const int inflate_threshold = 50;
static const int halve_threshold_root = 15;
static const int inflate_threshold_root = 30;

static void __alias_free_mem(struct rcu_head *head)
{
	struct fib_alias *fa = container_of(head, struct fib_alias, rcu);
	kmem_cache_free(fn_alias_kmem, fa);
}

static inline void alias_free_mem_rcu(struct fib_alias *fa)
{
	call_rcu(&fa->rcu, __alias_free_mem);
}

#define TNODE_KMALLOC_MAX \
	ilog2((PAGE_SIZE - TNODE_SIZE(0)) / sizeof(struct key_vector *))
#define TNODE_VMALLOC_MAX \
	ilog2((SIZE_MAX - TNODE_SIZE(0)) / sizeof(struct key_vector *))

static void __node_free_rcu(struct rcu_head *head)
{
	struct tnode *n = container_of(head, struct tnode, rcu);

	if (!n->tn_bits)
		kmem_cache_free(trie_leaf_kmem, n);
	else
		kvfree(n);
}

#define node_free(n) call_rcu(&tn_info(n)->rcu, __node_free_rcu)

static struct tnode *tnode_alloc(int bits)
{
	size_t size;

	/* verify bits is within bounds */
	if (bits > TNODE_VMALLOC_MAX)
		return NULL;

	/* determine size and verify it is non-zero and didn't overflow */
	size = TNODE_SIZE(1ul << bits);

	if (size <= PAGE_SIZE)
		return kzalloc(size, GFP_KERNEL);
	else
		return vzalloc(size);
}

static inline void empty_child_inc(struct key_vector *n)
{
	++tn_info(n)->empty_children ? : ++tn_info(n)->full_children;
}

static inline void empty_child_dec(struct key_vector *n)
{
	tn_info(n)->empty_children-- ? : tn_info(n)->full_children--;
}

static struct key_vector *leaf_new(t_key key, struct fib_alias *fa)
{
	struct key_vector *l;
	struct tnode *kv;

	kv = kmem_cache_alloc(trie_leaf_kmem, GFP_KERNEL);
	if (!kv)
		return NULL;

	/* initialize key vector */
	l = kv->kv;
	l->key = key;
	l->pos = 0;
	l->bits = 0;
	l->slen = fa->fa_slen;

	/* link leaf to fib alias */
	INIT_HLIST_HEAD(&l->leaf);
	hlist_add_head(&fa->fa_list, &l->leaf);

	return l;
}

static struct key_vector *tnode_new(t_key key, int pos, int bits)
{
	unsigned int shift = pos + bits;
	struct key_vector *tn;
	struct tnode *tnode;

	/* verify bits and pos their msb bits clear and values are valid */
	BUG_ON(!bits || (shift > KEYLENGTH));

	tnode = tnode_alloc(bits);
	if (!tnode)
		return NULL;

	pr_debug("AT %p s=%zu %zu\n", tnode, TNODE_SIZE(0),
		 sizeof(struct key_vector *) << bits);

	if (bits == KEYLENGTH)
		tnode->full_children = 1;
	else
		tnode->empty_children = 1ul << bits;

	tn = tnode->kv;
	tn->key = (shift < KEYLENGTH) ? (key >> shift) << shift : 0;
	tn->pos = pos;
	tn->bits = bits;
	tn->slen = pos;

	return tn;
}

/* Check whether a tnode 'n' is "full", i.e. it is an internal node
 * and no bits are skipped. See discussion in dyntree paper p. 6
 */
static inline int tnode_full(struct key_vector *tn, struct key_vector *n)
{
	return n && ((n->pos + n->bits) == tn->pos) && IS_TNODE(n);
}

/* Add a child at position i overwriting the old value.
 * Update the value of full_children and empty_children.
 */
static void put_child(struct key_vector *tn, unsigned long i,
		      struct key_vector *n)
{
	struct key_vector *chi = get_child(tn, i);
	int isfull, wasfull;

	BUG_ON(i >= child_length(tn));

	/* update emptyChildren, overflow into fullChildren */
	if (!n && chi)
		empty_child_inc(tn);
	if (n && !chi)
		empty_child_dec(tn);

	/* update fullChildren */
	wasfull = tnode_full(tn, chi);
	isfull = tnode_full(tn, n);

	if (wasfull && !isfull)
		tn_info(tn)->full_children--;
	else if (!wasfull && isfull)
		tn_info(tn)->full_children++;

	if (n && (tn->slen < n->slen))
		tn->slen = n->slen;

	rcu_assign_pointer(tn->tnode[i], n);
}

static void update_children(struct key_vector *tn)
{
	unsigned long i;

	/* update all of the child parent pointers */
	for (i = child_length(tn); i;) {
		struct key_vector *inode = get_child(tn, --i);

		if (!inode)
			continue;

		/* Either update the children of a tnode that
		 * already belongs to us or update the child
		 * to point to ourselves.
		 */
		if (node_parent(inode) == tn)
			update_children(inode);
		else
			node_set_parent(inode, tn);
	}
}

static inline void put_child_root(struct key_vector *tp, t_key key,
				  struct key_vector *n)
{
	if (IS_TRIE(tp))
		rcu_assign_pointer(tp->tnode[0], n);
	else
		put_child(tp, get_index(key, tp), n);
}

static inline void tnode_free_init(struct key_vector *tn)
{
	tn_info(tn)->rcu.next = NULL;
}

static inline void tnode_free_append(struct key_vector *tn,
				     struct key_vector *n)
{
	tn_info(n)->rcu.next = tn_info(tn)->rcu.next;
	tn_info(tn)->rcu.next = &tn_info(n)->rcu;
}

static void tnode_free(struct key_vector *tn)
{
	struct callback_head *head = &tn_info(tn)->rcu;

	while (head) {
		head = head->next;
		tnode_free_size += TNODE_SIZE(1ul << tn->bits);
		node_free(tn);

		tn = container_of(head, struct tnode, rcu)->kv;
	}

	if (tnode_free_size >= PAGE_SIZE * sync_pages) {
		tnode_free_size = 0;
		synchronize_rcu();
	}
}

static struct key_vector *replace(struct trie *t,
				  struct key_vector *oldtnode,
				  struct key_vector *tn)
{
	struct key_vector *tp = node_parent(oldtnode);
	unsigned long i;

	/* setup the parent pointer out of and back into this node */
	NODE_INIT_PARENT(tn, tp);
	put_child_root(tp, tn->key, tn);

	/* update all of the child parent pointers */
	update_children(tn);

	/* all pointers should be clean so we are done */
	tnode_free(oldtnode);

	/* resize children now that oldtnode is freed */
	for (i = child_length(tn); i;) {
		struct key_vector *inode = get_child(tn, --i);

		/* resize child node */
		if (tnode_full(tn, inode))
			tn = resize(t, inode);
	}

	return tp;
}

static struct key_vector *inflate(struct trie *t,
				  struct key_vector *oldtnode)
{
	struct key_vector *tn;
	unsigned long i;
	t_key m;

	pr_debug("In inflate\n");

	tn = tnode_new(oldtnode->key, oldtnode->pos - 1, oldtnode->bits + 1);
	if (!tn)
		goto notnode;

	/* prepare oldtnode to be freed */
	tnode_free_init(oldtnode);

	/* Assemble all of the pointers in our cluster, in this case that
	 * represents all of the pointers out of our allocated nodes that
	 * point to existing tnodes and the links between our allocated
	 * nodes.
	 */
	for (i = child_length(oldtnode), m = 1u << tn->pos; i;) {
		struct key_vector *inode = get_child(oldtnode, --i);
		struct key_vector *node0, *node1;
		unsigned long j, k;

		/* An empty child */
		if (!inode)
			continue;

		/* A leaf or an internal node with skipped bits */
		if (!tnode_full(oldtnode, inode)) {
			put_child(tn, get_index(inode->key, tn), inode);
			continue;
		}

		/* drop the node in the old tnode free list */
		tnode_free_append(oldtnode, inode);

		/* An internal node with two children */
		if (inode->bits == 1) {
			put_child(tn, 2 * i + 1, get_child(inode, 1));
			put_child(tn, 2 * i, get_child(inode, 0));
			continue;
		}

		/* We will replace this node 'inode' with two new
		 * ones, 'node0' and 'node1', each with half of the
		 * original children. The two new nodes will have
		 * a position one bit further down the key and this
		 * means that the "significant" part of their keys
		 * (see the discussion near the top of this file)
		 * will differ by one bit, which will be "0" in
		 * node0's key and "1" in node1's key. Since we are
		 * moving the key position by one step, the bit that
		 * we are moving away from - the bit at position
		 * (tn->pos) - is the one that will differ between
		 * node0 and node1. So... we synthesize that bit in the
		 * two new keys.
		 */
		node1 = tnode_new(inode->key | m, inode->pos, inode->bits - 1);
		if (!node1)
			goto nomem;
		node0 = tnode_new(inode->key, inode->pos, inode->bits - 1);

		tnode_free_append(tn, node1);
		if (!node0)
			goto nomem;
		tnode_free_append(tn, node0);

		/* populate child pointers in new nodes */
		for (k = child_length(inode), j = k / 2; j;) {
			put_child(node1, --j, get_child(inode, --k));
			put_child(node0, j, get_child(inode, j));
			put_child(node1, --j, get_child(inode, --k));
			put_child(node0, j, get_child(inode, j));
		}

		/* link new nodes to parent */
		NODE_INIT_PARENT(node1, tn);
		NODE_INIT_PARENT(node0, tn);

		/* link parent to nodes */
		put_child(tn, 2 * i + 1, node1);
		put_child(tn, 2 * i, node0);
	}

	/* setup the parent pointers into and out of this node */
	return replace(t, oldtnode, tn);
nomem:
	/* all pointers should be clean so we are done */
	tnode_free(tn);
notnode:
	return NULL;
}

static struct key_vector *halve(struct trie *t,
				struct key_vector *oldtnode)
{
	struct key_vector *tn;
	unsigned long i;

	pr_debug("In halve\n");

	tn = tnode_new(oldtnode->key, oldtnode->pos + 1, oldtnode->bits - 1);
	if (!tn)
		goto notnode;

	/* prepare oldtnode to be freed */
	tnode_free_init(oldtnode);

	/* Assemble all of the pointers in our cluster, in this case that
	 * represents all of the pointers out of our allocated nodes that
	 * point to existing tnodes and the links between our allocated
	 * nodes.
	 */
	for (i = child_length(oldtnode); i;) {
		struct key_vector *node1 = get_child(oldtnode, --i);
		struct key_vector *node0 = get_child(oldtnode, --i);
		struct key_vector *inode;

		/* At least one of the children is empty */
		if (!node1 || !node0) {
			put_child(tn, i / 2, node1 ? : node0);
			continue;
		}

		/* Two nonempty children */
		inode = tnode_new(node0->key, oldtnode->pos, 1);
		if (!inode)
			goto nomem;
		tnode_free_append(tn, inode);

		/* initialize pointers out of node */
		put_child(inode, 1, node1);
		put_child(inode, 0, node0);
		NODE_INIT_PARENT(inode, tn);

		/* link parent to node */
		put_child(tn, i / 2, inode);
	}

	/* setup the parent pointers into and out of this node */
	return replace(t, oldtnode, tn);
nomem:
	/* all pointers should be clean so we are done */
	tnode_free(tn);
notnode:
	return NULL;
}

static struct key_vector *collapse(struct trie *t,
				   struct key_vector *oldtnode)
{
	struct key_vector *n, *tp;
	unsigned long i;

	/* scan the tnode looking for that one child that might still exist */
	for (n = NULL, i = child_length(oldtnode); !n && i;)
		n = get_child(oldtnode, --i);

	/* compress one level */
	tp = node_parent(oldtnode);
	put_child_root(tp, oldtnode->key, n);
	node_set_parent(n, tp);

	/* drop dead node */
	node_free(oldtnode);

	return tp;
}

static unsigned char update_suffix(struct key_vector *tn)
{
	unsigned char slen = tn->pos;
	unsigned long stride, i;
	unsigned char slen_max;

	/* only vector 0 can have a suffix length greater than or equal to
	 * tn->pos + tn->bits, the second highest node will have a suffix
	 * length at most of tn->pos + tn->bits - 1
	 */
	slen_max = min_t(unsigned char, tn->pos + tn->bits - 1, tn->slen);

	/* search though the list of children looking for nodes that might
	 * have a suffix greater than the one we currently have.  This is
	 * why we start with a stride of 2 since a stride of 1 would
	 * represent the nodes with suffix length equal to tn->pos
	 */
	for (i = 0, stride = 0x2ul ; i < child_length(tn); i += stride) {
		struct key_vector *n = get_child(tn, i);

		if (!n || (n->slen <= slen))
			continue;

		/* update stride and slen based on new value */
		stride <<= (n->slen - slen);
		slen = n->slen;
		i &= ~(stride - 1);

		/* stop searching if we have hit the maximum possible value */
		if (slen >= slen_max)
			break;
	}

	tn->slen = slen;

	return slen;
}

/* From "Implementing a dynamic compressed trie" by Stefan Nilsson of
 * the Helsinki University of Technology and Matti Tikkanen of Nokia
 * Telecommunications, page 6:
 * "A node is doubled if the ratio of non-empty children to all
 * children in the *doubled* node is at least 'high'."
 *
 * 'high' in this instance is the variable 'inflate_threshold'. It
 * is expressed as a percentage, so we multiply it with
 * child_length() and instead of multiplying by 2 (since the
 * child array will be doubled by inflate()) and multiplying
 * the left-hand side by 100 (to handle the percentage thing) we
 * multiply the left-hand side by 50.
 *
 * The left-hand side may look a bit weird: child_length(tn)
 * - tn->empty_children is of course the number of non-null children
 * in the current node. tn->full_children is the number of "full"
 * children, that is non-null tnodes with a skip value of 0.
 * All of those will be doubled in the resulting inflated tnode, so
 * we just count them one extra time here.
 *
 * A clearer way to write this would be:
 *
 * to_be_doubled = tn->full_children;
 * not_to_be_doubled = child_length(tn) - tn->empty_children -
 *     tn->full_children;
 *
 * new_child_length = child_length(tn) * 2;
 *
 * new_fill_factor = 100 * (not_to_be_doubled + 2*to_be_doubled) /
 *      new_child_length;
 * if (new_fill_factor >= inflate_threshold)
 *
 * ...and so on, tho it would mess up the while () loop.
 *
 * anyway,
 * 100 * (not_to_be_doubled + 2*to_be_doubled) / new_child_length >=
 *      inflate_threshold
 *
 * avoid a division:
 * 100 * (not_to_be_doubled + 2*to_be_doubled) >=
 *      inflate_threshold * new_child_length
 *
 * expand not_to_be_doubled and to_be_doubled, and shorten:
 * 100 * (child_length(tn) - tn->empty_children +
 *    tn->full_children) >= inflate_threshold * new_child_length
 *
 * expand new_child_length:
 * 100 * (child_length(tn) - tn->empty_children +
 *    tn->full_children) >=
 *      inflate_threshold * child_length(tn) * 2
 *
 * shorten again:
 * 50 * (tn->full_children + child_length(tn) -
 *    tn->empty_children) >= inflate_threshold *
 *    child_length(tn)
 *
 */
static inline bool should_inflate(struct key_vector *tp, struct key_vector *tn)
{
	unsigned long used = child_length(tn);
	unsigned long threshold = used;

	/* Keep root node larger */
	threshold *= IS_TRIE(tp) ? inflate_threshold_root : inflate_threshold;
	used -= tn_info(tn)->empty_children;
	used += tn_info(tn)->full_children;

	/* if bits == KEYLENGTH then pos = 0, and will fail below */

	return (used > 1) && tn->pos && ((50 * used) >= threshold);
}

static inline bool should_halve(struct key_vector *tp, struct key_vector *tn)
{
	unsigned long used = child_length(tn);
	unsigned long threshold = used;

	/* Keep root node larger */
	threshold *= IS_TRIE(tp) ? halve_threshold_root : halve_threshold;
	used -= tn_info(tn)->empty_children;

	/* if bits == KEYLENGTH then used = 100% on wrap, and will fail below */

	return (used > 1) && (tn->bits > 1) && ((100 * used) < threshold);
}

static inline bool should_collapse(struct key_vector *tn)
{
	unsigned long used = child_length(tn);

	used -= tn_info(tn)->empty_children;

	/* account for bits == KEYLENGTH case */
	if ((tn->bits == KEYLENGTH) && tn_info(tn)->full_children)
		used -= KEY_MAX;

	/* One child or none, time to drop us from the trie */
	return used < 2;
}

#define MAX_WORK 10
static struct key_vector *resize(struct trie *t, struct key_vector *tn)
{
#ifdef CONFIG_IP_FIB_TRIE_STATS
	struct trie_use_stats __percpu *stats = t->stats;
#endif
	struct key_vector *tp = node_parent(tn);
	unsigned long cindex = get_index(tn->key, tp);
	int max_work = MAX_WORK;

	pr_debug("In tnode_resize %p inflate_threshold=%d threshold=%d\n",
		 tn, inflate_threshold, halve_threshold);

	/* track the tnode via the pointer from the parent instead of
	 * doing it ourselves.  This way we can let RCU fully do its
	 * thing without us interfering
	 */
	BUG_ON(tn != get_child(tp, cindex));

	/* Double as long as the resulting node has a number of
	 * nonempty nodes that are above the threshold.
	 */
	while (should_inflate(tp, tn) && max_work) {
		tp = inflate(t, tn);
		if (!tp) {
#ifdef CONFIG_IP_FIB_TRIE_STATS
			this_cpu_inc(stats->resize_node_skipped);
#endif
			break;
		}

		max_work--;
		tn = get_child(tp, cindex);
	}

	/* update parent in case inflate failed */
	tp = node_parent(tn);

	/* Return if at least one inflate is run */
	if (max_work != MAX_WORK)
		return tp;

	/* Halve as long as the number of empty children in this
	 * node is above threshold.
	 */
	while (should_halve(tp, tn) && max_work) {
		tp = halve(t, tn);
		if (!tp) {
#ifdef CONFIG_IP_FIB_TRIE_STATS
			this_cpu_inc(stats->resize_node_skipped);
#endif
			break;
		}

		max_work--;
		tn = get_child(tp, cindex);
	}

	/* Only one child remains */
	if (should_collapse(tn))
		return collapse(t, tn);

	/* update parent in case halve failed */
	return node_parent(tn);
}

static void node_pull_suffix(struct key_vector *tn, unsigned char slen)
{
	unsigned char node_slen = tn->slen;

	while ((node_slen > tn->pos) && (node_slen > slen)) {
		slen = update_suffix(tn);
		if (node_slen == slen)
			break;

		tn = node_parent(tn);
		node_slen = tn->slen;
	}
}

static void node_push_suffix(struct key_vector *tn, unsigned char slen)
{
	while (tn->slen < slen) {
		tn->slen = slen;
		tn = node_parent(tn);
	}
}

/* rcu_read_lock needs to be hold by caller from readside */
static struct key_vector *fib_find_node(struct trie *t,
					struct key_vector **tp, u32 key)
{
	struct key_vector *pn, *n = t->kv;
	unsigned long index = 0;

	do {
		pn = n;
		n = get_child_rcu(n, index);

		if (!n)
			break;

		index = get_cindex(key, n);

		/* This bit of code is a bit tricky but it combines multiple
		 * checks into a single check.  The prefix consists of the
		 * prefix plus zeros for the bits in the cindex. The index
		 * is the difference between the key and this value.  From
		 * this we can actually derive several pieces of data.
		 *   if (index >= (1ul << bits))
		 *     we have a mismatch in skip bits and failed
		 *   else
		 *     we know the value is cindex
		 *
		 * This check is safe even if bits == KEYLENGTH due to the
		 * fact that we can only allocate a node with 32 bits if a
		 * long is greater than 32 bits.
		 */
		if (index >= (1ul << n->bits)) {
			n = NULL;
			break;
		}

		/* keep searching until we find a perfect match leaf or NULL */
	} while (IS_TNODE(n));

	*tp = pn;

	return n;
}

/* Return the first fib alias matching TOS with
 * priority less than or equal to PRIO.
 */
static struct fib_alias *fib_find_alias(struct hlist_head *fah, u8 slen,
					u8 tos, u32 prio, u32 tb_id)
{
	struct fib_alias *fa;

	if (!fah)
		return NULL;

	hlist_for_each_entry(fa, fah, fa_list) {
		if (fa->fa_slen < slen)
			continue;
		if (fa->fa_slen != slen)
			break;
		if (fa->tb_id > tb_id)
			continue;
		if (fa->tb_id != tb_id)
			break;
		if (fa->fa_tos > tos)
			continue;
		if (fa->fa_info->fib_priority >= prio || fa->fa_tos < tos)
			return fa;
	}

	return NULL;
}

static void trie_rebalance(struct trie *t, struct key_vector *tn)
{
	while (!IS_TRIE(tn))
		tn = resize(t, tn);
}

static int fib_insert_node(struct trie *t, struct key_vector *tp,
			   struct fib_alias *new, t_key key)
{
	struct key_vector *n, *l;

	l = leaf_new(key, new);
	if (!l)
		goto noleaf;

	/* retrieve child from parent node */
	n = get_child(tp, get_index(key, tp));

	/* Case 2: n is a LEAF or a TNODE and the key doesn't match.
	 *
	 *  Add a new tnode here
	 *  first tnode need some special handling
	 *  leaves us in position for handling as case 3
	 */
	if (n) {
		struct key_vector *tn;

		tn = tnode_new(key, __fls(key ^ n->key), 1);
		if (!tn)
			goto notnode;

		/* initialize routes out of node */
		NODE_INIT_PARENT(tn, tp);
		put_child(tn, get_index(key, tn) ^ 1, n);

		/* start adding routes into the node */
		put_child_root(tp, key, tn);
		node_set_parent(n, tn);

		/* parent now has a NULL spot where the leaf can go */
		tp = tn;
	}

	/* Case 3: n is NULL, and will just insert a new leaf */
	node_push_suffix(tp, new->fa_slen);
	NODE_INIT_PARENT(l, tp);
	put_child_root(tp, key, l);
	trie_rebalance(t, tp);

	return 0;
notnode:
	node_free(l);
noleaf:
	return -ENOMEM;
}

/* fib notifier for ADD is sent before calling fib_insert_alias with
 * the expectation that the only possible failure ENOMEM
 */
static int fib_insert_alias(struct trie *t, struct key_vector *tp,
			    struct key_vector *l, struct fib_alias *new,
			    struct fib_alias *fa, t_key key)
{
	if (!l)
		return fib_insert_node(t, tp, new, key);

	if (fa) {
		hlist_add_before_rcu(&new->fa_list, &fa->fa_list);
	} else {
		struct fib_alias *last;

		hlist_for_each_entry(last, &l->leaf, fa_list) {
			if (new->fa_slen < last->fa_slen)
				break;
			if ((new->fa_slen == last->fa_slen) &&
			    (new->tb_id > last->tb_id))
				break;
			fa = last;
		}

		if (fa)
			hlist_add_behind_rcu(&new->fa_list, &fa->fa_list);
		else
			hlist_add_head_rcu(&new->fa_list, &l->leaf);
	}

	/* if we added to the tail node then we need to update slen */
	if (l->slen < new->fa_slen) {
		l->slen = new->fa_slen;
		node_push_suffix(tp, new->fa_slen);
	}

	return 0;
}

static bool fib_valid_key_len(u32 key, u8 plen, struct netlink_ext_ack *extack)
{
	if (plen > KEYLENGTH) {
		NL_SET_ERR_MSG(extack, "Invalid prefix length");
		return false;
	}

	if ((plen < KEYLENGTH) && (key << plen)) {
		NL_SET_ERR_MSG(extack,
			       "Invalid prefix for given prefix length");
		return false;
	}

	return true;
}

/* Caller must hold RTNL. */
int fib_table_insert(struct net *net, struct fib_table *tb,
		     struct fib_config *cfg, struct netlink_ext_ack *extack)
{
	enum fib_event_type event = FIB_EVENT_ENTRY_ADD;
	struct trie *t = (struct trie *)tb->tb_data;