Reimplementation of prefix sets.

Prefix sets were broken beyond any repair and have to be reimplemented.
They are reimplemented using a trie with bitmasks in nodes.
There is also change in the interpretation of minus prefix pattern,
but the old interpretation was already inconsistent with
the documentation and broken.

There is also some bugfixes in filter code related to set variables.

1 files changed, 325 insertions, 0 deletions

diff --git a/filter/trie.c b/filter/trie.c
new file mode 100644
index 0000000..7f9f5f8
--- /dev/null
+++ b/filter/trie.c
@@ -0,0 +1,325 @@
+/*
+ *	Filters: Trie for prefix sets
+ *
+ *	Copyright 2009 Ondrej Zajicek <santiago@crfreenet.org>
+ *
+ *	Can be freely distributed and used under the terms of the GNU GPL.
+ */
+
+/**
+ * DOC: Trie for prefix sets
+ *
+ * We use a (compressed) trie to represent prefix sets. Every node
+ * in the trie represents one prefix (&addr/&plen) and &plen also
+ * indicates the index of the bit in the address that is used to
+ * branch at the node. If we need to represent just a set of
+ * prefixes, it would be simple, but we have to represent a
+ * set of prefix pattern. Each prefix pattern consists of
+ * &ppaddr/&pplen and two integers: &low and &high, and a prefix
+ * &paddr/&plen matches that pattern if the first MIN(&plen, &pplen)
+ * bits of &paddr and &ppaddr are the same and &low <= &plen <= &high.
+ *
+ * We use a bitmask (&accept) to represent accepted prefix lengths
+ * at a node. As there are 33 prefix lengths (0..32 for IPv4), but
+ * there is just one prefix of zero length in the whole trie so we 
+ * have &zero flag in &f_trie (indicating whether the trie accepts
+ * prefix 0.0.0.0/0) as a special case, and &accept bitmask
+ * represents accepted prefix lengths from 1 to 32.
+ *
+ * There are two cases in prefix matching - a match when the length
+ * of the prefix is smaller that the length of the prefix pattern,
+ * (&plen < &pplen) and otherwise. The second case is simple - we
+ * just walk through the trie and look at every visited node
+ * whether that prefix accepts our prefix length (&plen). The
+ * first case is tricky - we don't want to examine every descendant
+ * of a final node, so (when we create the trie) we have to propagate
+ * that information from nodes to their ascendants.
+ *
+ * Suppose that we have two masks (M1 and M2) for a node. Mask M1
+ * represents accepted prefix lengths by just the node and mask M2
+ * represents accepted prefix lengths by the node or any of its
+ * descendants. Therefore M2 is a bitwise or of M1 and children's
+ * M2 and this is a maintained invariant during trie building.
+ * Basically, when we want to match a prefix, we walk through the trie,
+ * check mask M1 for our prefix length and when we came to
+ * final node, we check mask M2.
+ *
+ * There are two differences in the real implementation. First,
+ * we use a compressed trie so there is a case that we skip our
+ * final node (if it is not in the trie) and we came to node that
+ * is either extension of our prefix, or completely out of path
+ * In the first case, we also have to check M2.
+
+ * There also might be
+ * a problem that interval of acceptance (on path from root to the
+ * final node) might be completely missing (for example if we have
+ * prefix patterns 192.168.128.0/24{8,10} and 192.168.1.0/24
+ *
+ * Second, we really need not to maintain two separate bitmasks.
+ * Checks for mask M1 are always larger than &applen and we need
+ * just the first &pplen bits of mask M2 (if trie compression
+ * hadn't been used it would suffice to know just $applen-th bit),
+ * so we have to store them together in &accept mask - the first
+ * &pplen bits of mask M2 and then mask M1.
+ *
+ * There are four cases when we walk through a trie:
+ *
+ * - we are in NULL
+ * - we are out of path (prefixes are inconsistent)
+ * - we are in the wanted (final) node (node length == &plen)
+ * - we are beyond the end of path (node length > &plen)
+ * - we are still on path and keep walking (node length < &plen)
+ *
+ * The walking code in add_node_to_trie() and trie_match_prefix()
+ * is structured according to these cases.
+ */
+
+#include "nest/bird.h"
+#include "conf/conf.h"
+#include "filter/filter.h"
+
+/**
+ * f_new_trie
+ *
+ * Allocates and returns a new empty trie.
+ */
+struct f_trie *
+f_new_trie(void)
+{
+  struct f_trie * ret;
+  ret = cfg_allocz(sizeof(struct f_trie));
+  return ret;
+}
+
+static inline struct f_trie_node *
+new_node(int plen, ip_addr paddr, ip_addr pmask, ip_addr amask)
+{
+  struct f_trie_node *n = cfg_allocz(sizeof(struct f_trie_node));
+  n->plen = plen;
+  n->addr = paddr;
+  n->mask = pmask;
+  n->accept = amask;
+  return n;
+}
+
+static inline void
+attach_node(struct f_trie_node *parent, struct f_trie_node *child)
+{
+  parent->c[ipa_getbit(child->addr, parent->plen) ? 1 : 0] = child;
+}
+
+static void
+add_node_to_trie(struct f_trie *t, int plen, ip_addr ip, ip_addr amask)
+{
+  ip_addr pmask = ipa_mkmask(plen);
+  ip_addr paddr = ipa_and(ip, pmask);
+  struct f_trie_node *o = NULL;
+  struct f_trie_node *n = &t->root;
+
+  while(n)
+    {
+      ip_addr cmask = ipa_and(n->mask, pmask);
+
+      if (ipa_compare(ipa_and(paddr, cmask), ipa_and(n->addr, cmask)))
+	{
+	  /* We are out of path - we have to add branching node 'b'
+	     between node 'o' and node 'n', and attach new node 'a'
+	     as the other child of 'b'. */
+	  int blen = ipa_pxlen(paddr, n->addr);
+	  ip_addr bmask = ipa_mkmask(blen);
+	  ip_addr baddr = ipa_and(ip, bmask);
+
+	  /* Merge accept masks from children to get accept mask for node 'b' */
+	  ip_addr baccm = ipa_and(ipa_or(amask, n->accept), bmask);
+
+	  struct f_trie_node *a = new_node(plen, paddr, pmask, amask);
+	  struct f_trie_node *b = new_node(blen, baddr, bmask, baccm);
+	  attach_node(o, b);
+	  attach_node(b, n);
+	  attach_node(b, a);
+	  return;
+	}
+
+      if (plen < n->plen)
+	{
+	  /* We add new node 'a' between node 'o' and node 'n' */
+	  amask = ipa_or(amask, ipa_and(n->accept, pmask));
+	  struct f_trie_node *a = new_node(plen, paddr, pmask, amask);
+	  attach_node(o, a);
+	  attach_node(a, n);
+	  return;
+	}
+	
+      if (plen == n->plen)
+	{
+	  /* We already found added node in trie. Just update accept mask */
+	  n->accept = ipa_or(n->accept, amask);
+	  return;
+	}
+
+      /* Update accept mask part M2 and go deeper */
+      n->accept = ipa_or(n->accept, ipa_and(amask, n->mask));
+
+      /* n->plen < plen and plen <= 32 */
+      o = n;
+      n = n->c[ipa_getbit(paddr, n->plen) ? 1 : 0];
+    }
+
+  /* We add new tail node 'a' after node 'o' */
+  struct f_trie_node *a = new_node(plen, paddr, pmask, amask);
+  attach_node(o, a);
+}
+
+/**
+ * trie_add_prefix
+ * @t: trie to add to
+ * @px: prefix to add
+ *
+ * Adds prefix (prefix pattern) @px to trie @t.
+ */
+void
+trie_add_prefix(struct f_trie *t, struct f_prefix *px)
+{
+  int l, h;
+  int plen = px->len & LEN_MASK;
+  ip_addr pmask = ipa_mkmask(plen);
+
+  /* 'l' and 'h' are lower and upper bounds on accepted
+     prefix lengths, both inclusive. 0 <= l, h <= 32 */
+  f_prefix_get_bounds(px, &l, &h);
+
+  if (l == 0)
+    t->zero = 1;
+  else
+    l--;
+
+  ip_addr amask = ipa_xor(ipa_mkmask(l), ipa_mkmask(h));
+  /* MIN(plen, h) instead of just plen is a little trick. */
+  add_node_to_trie(t, MIN(plen, h), px->ip, amask);
+}
+
+/**
+ * trie_match_prefix
+ * @t: trie
+ * @px: prefix
+ *
+ * Tries to find a matching prefix pattern in the trie such that
+ * prefix @px matches that prefix pattern. Returns 1 if there
+ * is such prefix pattern in the trie.
+ */
+int
+trie_match_prefix(struct f_trie *t, struct f_prefix *px)
+{
+  int plen = px->len & LEN_MASK;
+  ip_addr pmask = ipa_mkmask(plen);
+  ip_addr paddr = ipa_and(px->ip, pmask);
+
+  if (plen == 0)
+    return t->zero;
+
+  int plentest = plen - 1;
+  struct f_trie_node *n = &t->root;
+
+  while(n)
+    {
+      ip_addr cmask = ipa_and(n->mask, pmask);
+
+      /* We are out of path */
+      if (ipa_compare(ipa_and(paddr, cmask), ipa_and(n->addr, cmask)))
+	return 0;
+
+      /* Check accept mask */
+      if (ipa_getbit(n->accept, plentest))
+	return 1;
+
+      /* We finished trie walk and still no match */
+      if (plen <= n->plen)
+	return 0;
+
+      /* Choose children */
+      n =  n->c[(ipa_getbit(paddr, n->plen)) ? 1 : 0];
+    }
+
+  return 0;
+}
+
+static int
+trie_node_same(struct f_trie_node *t1, struct f_trie_node *t2)
+{
+  if ((t1 == NULL) && (t2 == NULL))
+    return 1;
+
+  if ((t1 == NULL) || (t2 == NULL))
+    return 0;
+
+  if ((t1->plen != t2->plen) ||
+      (! ipa_equal(t1->addr, t2->addr)) ||
+      (! ipa_equal(t1->accept, t2->accept)))
+    return 0;
+
+  return trie_node_same(t1->c[0], t2->c[0]) && trie_node_same(t1->c[1], t2->c[1]);
+}
+
+/**
+ * trie_same
+ * @t1: first trie to be compared
+ * @t2: second one
+ *
+ * Compares two tries and returns 1 if they are same
+ */
+int
+trie_same(struct f_trie *t1, struct f_trie *t2)
+{
+  return (t1->zero == t2->zero) && trie_node_same(&t1->root, &t2->root);
+}
+
+static int
+trie_node_print(struct f_trie_node *t, char *buf, int blen)
+{
+  if (t == NULL)
+    return;
+
+  int old_blen = blen;
+  int wb = 0; // bsnprintf(buf, blen, "%I/%d accept %I\n", t->addr, t->plen, t->accept);
+debug("%I/%d accept %I\n", t->addr, t->plen, t->accept);
+
+  if ((wb < 0) || ((blen - wb) < 10))
+    {
+      bsnprintf(buf, blen, "...\n");
+      return -1;
+    }
+
+  buf += wb;
+  blen -= wb;
+
+  wb = trie_node_print(t->c[0], buf, blen);
+  if (wb < 0)
+    return -1;
+
+  buf += wb;
+  blen -= wb;
+
+  wb = trie_node_print(t->c[1], buf, blen);
+  if (wb < 0)
+    return -1;
+
+  blen -= wb;
+
+  return (old_blen - blen);
+}
+
+/**
+ * trie_print
+ * @t: trie to be printed
+ * @buf: buffer
+ * @blen: buffer length
+ *
+ * Prints the trie to the buffer, using at most blen bytes.
+ * Returns the number of used bytes, or -1 if there is not
+ * enough space in the buffer.
+ */
+int
+trie_print(struct f_trie *t, char *buf, int blen)
+{
+  return trie_node_print(&t->root, buf, blen);
+}