#define IS_TNODE(n) ((n)->bits)
#define IS_LEAF(n) (!(n)->bits)
+#define get_shift(_kv) (KEYLENGTH - (_kv)->pos - (_kv)->bits)
+#define get_index(_key, _kv) (((_key) ^ (_kv)->key) >> get_shift(_kv))
+
struct tnode {
t_key key;
unsigned char bits; /* 2log(KEYLENGTH) bits needed */
continue;
fib_alias_accessed(fa);
err = fib_props[fa->fa_type].error;
- if (err) {
+ if (unlikely(err < 0)) {
#ifdef CONFIG_IP_FIB_TRIE_STATS
this_cpu_inc(t->stats->semantic_match_passed);
#endif
res->prefixlen = li->plen;
res->nh_sel = nhsel;
res->type = fa->fa_type;
- res->scope = fa->fa_info->fib_scope;
+ res->scope = fi->fib_scope;
res->fi = fi;
res->table = tb;
res->fa_head = &li->falh;
return 1;
}
+static inline t_key prefix_mismatch(t_key key, struct tnode *n)
+{
+ t_key prefix = n->key;
+
+ return (key ^ prefix) & (prefix | -prefix);
+}
+
int fib_table_lookup(struct fib_table *tb, const struct flowi4 *flp,
struct fib_result *res, int fib_flags)
{
- struct trie *t = (struct trie *) tb->tb_data;
+ struct trie *t = (struct trie *)tb->tb_data;
#ifdef CONFIG_IP_FIB_TRIE_STATS
struct trie_use_stats __percpu *stats = t->stats;
#endif
- int ret;
- struct tnode *n;
- struct tnode *pn;
- unsigned int pos, bits;
- t_key key = ntohl(flp->daddr);
- unsigned int chopped_off;
- t_key cindex = 0;
- unsigned int current_prefix_length = KEYLENGTH;
- struct tnode *cn;
- t_key pref_mismatch;
+ const t_key key = ntohl(flp->daddr);
+ struct tnode *n, *pn;
+ t_key cindex;
+ int ret = 1;
rcu_read_lock();
this_cpu_inc(stats->gets);
#endif
- /* Just a leaf? */
- if (IS_LEAF(n)) {
- ret = check_leaf(tb, t, n, key, flp, res, fib_flags);
- goto found;
- }
-
pn = n;
- chopped_off = 0;
-
- while (pn) {
- pos = pn->pos;
- bits = pn->bits;
-
- if (!chopped_off)
- cindex = tkey_extract_bits(mask_pfx(key, current_prefix_length),
- pos, bits);
-
- n = tnode_get_child_rcu(pn, cindex);
-
- if (n == NULL) {
-#ifdef CONFIG_IP_FIB_TRIE_STATS
- this_cpu_inc(stats->null_node_hit);
-#endif
- goto backtrace;
- }
+ cindex = 0;
+
+ /* Step 1: Travel to the longest prefix match in the trie */
+ for (;;) {
+ unsigned long index = get_index(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 prefix. The index
+ * is the difference between the key and this value. From
+ * this we can actually derive several pieces of data.
+ * if !(index >> bits)
+ * we know the value is child index
+ * else
+ * we have a mismatch in skip bits and failed
+ */
+ if (index >> n->bits)
+ break;
- if (IS_LEAF(n)) {
- ret = check_leaf(tb, t, n, key, flp, res, fib_flags);
- if (ret > 0)
- goto backtrace;
+ /* we have found a leaf. Prefixes have already been compared */
+ if (IS_LEAF(n))
goto found;
- }
- cn = n;
-
- /*
- * It's a tnode, and we can do some extra checks here if we
- * like, to avoid descending into a dead-end branch.
- * This tnode is in the parent's child array at index
- * key[p_pos..p_pos+p_bits] but potentially with some bits
- * chopped off, so in reality the index may be just a
- * subprefix, padded with zero at the end.
- * We can also take a look at any skipped bits in this
- * tnode - everything up to p_pos is supposed to be ok,
- * and the non-chopped bits of the index (se previous
- * paragraph) are also guaranteed ok, but the rest is
- * considered unknown.
- *
- * The skipped bits are key[pos+bits..cn->pos].
- */
-
- /* If current_prefix_length < pos+bits, we are already doing
- * actual prefix matching, which means everything from
- * pos+(bits-chopped_off) onward must be zero along some
- * branch of this subtree - otherwise there is *no* valid
- * prefix present. Here we can only check the skipped
- * bits. Remember, since we have already indexed into the
- * parent's child array, we know that the bits we chopped of
- * *are* zero.
+ /* only record pn and cindex if we are going to be chopping
+ * bits later. Otherwise we are just wasting cycles.
*/
-
- /* NOTA BENE: Checking only skipped bits
- for the new node here */
-
- if (current_prefix_length < pos+bits) {
- if (tkey_extract_bits(cn->key, current_prefix_length,
- cn->pos - current_prefix_length)
- || !(cn->child[0]))
- goto backtrace;
+ if (index) {
+ pn = n;
+ cindex = index;
}
- /*
- * If chopped_off=0, the index is fully validated and we
- * only need to look at the skipped bits for this, the new,
- * tnode. What we actually want to do is to find out if
- * these skipped bits match our key perfectly, or if we will
- * have to count on finding a matching prefix further down,
- * because if we do, we would like to have some way of
- * verifying the existence of such a prefix at this point.
- */
+ n = rcu_dereference(n->child[index]);
+ if (unlikely(!n))
+ goto backtrace;
+ }
- /* The only thing we can do at this point is to verify that
- * any such matching prefix can indeed be a prefix to our
- * key, and if the bits in the node we are inspecting that
- * do not match our key are not ZERO, this cannot be true.
- * Thus, find out where there is a mismatch (before cn->pos)
- * and verify that all the mismatching bits are zero in the
- * new tnode's key.
- */
+ /* Step 2: Sort out leaves and begin backtracing for longest prefix */
+ for (;;) {
+ /* record the pointer where our next node pointer is stored */
+ struct tnode __rcu **cptr = n->child;
- /*
- * Note: We aren't very concerned about the piece of
- * the key that precede pn->pos+pn->bits, since these
- * have already been checked. The bits after cn->pos
- * aren't checked since these are by definition
- * "unknown" at this point. Thus, what we want to see
- * is if we are about to enter the "prefix matching"
- * state, and in that case verify that the skipped
- * bits that will prevail throughout this subtree are
- * zero, as they have to be if we are to find a
- * matching prefix.
+ /* This test verifies that none of the bits that differ
+ * between the key and the prefix exist in the region of
+ * the lsb and higher in the prefix.
*/
+ if (unlikely(prefix_mismatch(key, n)))
+ goto backtrace;
- pref_mismatch = mask_pfx(cn->key ^ key, cn->pos);
+ /* exit out and process leaf */
+ if (unlikely(IS_LEAF(n)))
+ break;
- /*
- * In short: If skipped bits in this node do not match
- * the search key, enter the "prefix matching"
- * state.directly.
+ /* Don't bother recording parent info. Since we are in
+ * prefix match mode we will have to come back to wherever
+ * we started this traversal anyway
*/
- if (pref_mismatch) {
- /* fls(x) = __fls(x) + 1 */
- int mp = KEYLENGTH - __fls(pref_mismatch) - 1;
-
- if (tkey_extract_bits(cn->key, mp, cn->pos - mp) != 0)
- goto backtrace;
-
- if (current_prefix_length >= cn->pos)
- current_prefix_length = mp;
- }
-
- pn = n; /* Descend */
- chopped_off = 0;
- continue;
+ while ((n = rcu_dereference(*cptr)) == NULL) {
backtrace:
- chopped_off++;
-
- /* As zero don't change the child key (cindex) */
- while ((chopped_off <= pn->bits)
- && !(cindex & (1<<(chopped_off-1))))
- chopped_off++;
-
- /* Decrease current_... with bits chopped off */
- if (current_prefix_length > pn->pos + pn->bits - chopped_off)
- current_prefix_length = pn->pos + pn->bits
- - chopped_off;
-
- /*
- * Either we do the actual chop off according or if we have
- * chopped off all bits in this tnode walk up to our parent.
- */
-
- if (chopped_off <= pn->bits) {
- cindex &= ~(1 << (chopped_off-1));
- } else {
- struct tnode *parent = node_parent_rcu(pn);
- if (!parent)
- goto failed;
-
- /* Get Child's index */
- cindex = tkey_extract_bits(pn->key, parent->pos, parent->bits);
- pn = parent;
- chopped_off = 0;
-
#ifdef CONFIG_IP_FIB_TRIE_STATS
- this_cpu_inc(stats->backtrack);
+ if (!n)
+ this_cpu_inc(stats->null_node_hit);
#endif
- goto backtrace;
+ /* If we are at cindex 0 there are no more bits for
+ * us to strip at this level so we must ascend back
+ * up one level to see if there are any more bits to
+ * be stripped there.
+ */
+ while (!cindex) {
+ t_key pkey = pn->key;
+
+ pn = node_parent_rcu(pn);
+ if (unlikely(!pn))
+ goto failed;
+#ifdef CONFIG_IP_FIB_TRIE_STATS
+ this_cpu_inc(stats->backtrack);
+#endif
+ /* Get Child's index */
+ cindex = get_index(pkey, pn);
+ }
+
+ /* strip the least significant bit from the cindex */
+ cindex &= cindex - 1;
+
+ /* grab pointer for next child node */
+ cptr = &pn->child[cindex];
}
}
-failed:
- ret = 1;
+
found:
+ /* Step 3: Process the leaf, if that fails fall back to backtracing */
+ ret = check_leaf(tb, t, n, key, flp, res, fib_flags);
+ if (unlikely(ret > 0))
+ goto backtrace;
+failed:
rcu_read_unlock();
return ret;
}
projects / cascardo / linux.git / blobdiff