+++ /dev/null
-/*
- * Copyright (c) 2008, 2011, 2012 Nicira, Inc.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at:
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-#ifndef TAG_H
-#define TAG_H 1
-
-#include <stdbool.h>
-#include <stdint.h>
-#include "util.h"
-
-/*
- * Tagging support.
- *
- * A 'tag' represents an arbitrary category. Currently, tags are used to
- * represent categories of flows and in particular the dependencies for a flow
- * switching decision. For example, if a flow's output port is based on
- * knowledge that source MAC 00:02:e3:0f:80:a4 is on eth0, then a tag that
- * represents that dependency is attached to that flow in the flowtracking hash
- * table.
- *
- * As this example shows, the universe of possible categories is very large,
- * and even the number of categories that are in use at a given time can be
- * very large. This means that keeping track of category membership via
- * conventional means (lists, bitmaps, etc.) is likely to be expensive.
- *
- * Tags are actually implemented via a "superimposed coding", as discussed in
- * Knuth TAOCP v.3 section 6.5 "Retrieval on Secondary Keys". A tag is an
- * unsigned integer in which exactly 2 bits are set to 1 and the rest set to 0.
- * For 32-bit integers (as currently used) there are 32 * 31 / 2 = 496 unique
- * tags; for 64-bit integers there are 64 * 63 / 2 = 2,016.
- *
- * Because there is a small finite number of unique tags, tags must collide
- * after some number of them have been created. In practice we generally
- * create tags by choosing bits randomly.
- *
- * The key property of tags is that we can combine them without increasing the
- * amount of data required using bitwise-OR, since the result has the 1-bits
- * from both tags set. The necessary tradeoff is that the result is even more
- * ambiguous: if combining two tags yields a value with 4 bits set to 1, then
- * the result value will test as having 4 * 3 / 2 = 6 unique tags, not just the
- * two tags that we combined.
- *
- * The upshot is this: a value that is the bitwise-OR combination of a number
- * of tags will always include the tags that were combined, but it may contain
- * any number of additional tags as well. This is acceptable for flowtracking,
- * since we want to be sure that we catch every flow that needs to be
- * revalidated, but it is OK if we revalidate a few extra flows as well.
- *
- * If we combine too many tags, then the result will have every bit set, so
- * that it will test as including every tag. Fortunately, this is not a big
- * problem for us: although there are many flows overall, each individual flow
- * belongs only to a small number of categories.
- */
-
-/* Represents a tag, or the combination of 0 or more tags. */
-typedef uint32_t tag_type;
-
-tag_type tag_create_random(void);
-tag_type tag_create_deterministic(uint32_t seed);
-static inline bool tag_intersects(tag_type, tag_type);
-static inline bool tag_is_valid(tag_type);
-
-/* Returns true if 'a' and 'b' have at least one tag in common,
- * false if their set of tags is disjoint. */
-static inline bool
-tag_intersects(tag_type a, tag_type b)
-{
- tag_type x = a & b;
- return (x & (x - 1)) != 0;
-}
-
-/* Returns true if 'tag' is a valid tag, that is, if exactly two bits are set
- * to 1 and the rest to 0. Otherwise, returns false. */
-static inline bool
-tag_is_valid(tag_type tag)
-{
- tag_type x = tag & (tag - 1);
- tag_type y = x & (x - 1);
- return x && !y;
-}
-\f
-/*
- * A tag set accumulates tags with reduced ambiguity compared to a single tag.
- * The flow tracking uses tag sets to keep track of tags that need to
- * revalidated after a number of packets have been processed.
- */
-#define TAG_SET_SIZE 4
-struct tag_set {
- tag_type total;
- tag_type tags[TAG_SET_SIZE];
- unsigned int n;
-};
-
-void tag_set_init(struct tag_set *);
-void tag_set_add(struct tag_set *, tag_type);
-void tag_set_union(struct tag_set *, const struct tag_set *);
-static inline bool tag_set_is_empty(const struct tag_set *);
-static inline bool tag_set_intersects(const struct tag_set *, tag_type);
-
-/* Returns true if 'set' will match no tags at all,
- * false if it will match at least one tag. */
-static inline bool
-tag_set_is_empty(const struct tag_set *set)
-{
- return !set->n;
-}
-
-/* Returns true if any of the tags in 'tags' are also in 'set',
- * false if the intersection is empty. */
-static inline bool
-tag_set_intersects(const struct tag_set *set, tag_type tags)
-{
- BUILD_ASSERT_DECL(TAG_SET_SIZE == 4);
- return (tag_intersects(set->total, tags)
- && (tag_intersects(set->tags[0], tags)
- || tag_intersects(set->tags[1], tags)
- || tag_intersects(set->tags[2], tags)
- || tag_intersects(set->tags[3], tags)));
-}
-
-#endif /* tag.h */
git://git.onelab.eu / sliver-openvswitch.git / blobdiff