--- /dev/null
+/* Copyright (c) 2008 The Board of Trustees of The Leland Stanford
+ * Junior University
+ *
+ * We are making the OpenFlow specification and associated documentation
+ * (Software) available for public use and benefit with the expectation
+ * that others will use, modify and enhance the Software and contribute
+ * those enhancements back to the community. However, since we would
+ * like to make the Software available for broadest use, with as few
+ * restrictions as possible permission is hereby granted, free of
+ * charge, to any person obtaining a copy of this Software to deal in
+ * the Software under the copyrights without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ * The name and trademarks of copyright holder(s) may NOT be used in
+ * advertising or publicity pertaining to the Software or any
+ * derivatives without specific, written prior permission.
+ */
+
+#include <config.h>
+#include "tag.h"
+#include <limits.h>
+#include "random.h"
+#include "type-props.h"
+#include "util.h"
+
+#define N_TAG_BITS (CHAR_BIT * sizeof(tag_type))
+BUILD_ASSERT_DECL(IS_POW2(N_TAG_BITS));
+
+#define LOG2_N_TAG_BITS (N_TAG_BITS == 32 ? 5 : N_TAG_BITS == 64 ? 6 : 0)
+BUILD_ASSERT_DECL(LOG2_N_TAG_BITS > 0);
+
+/* Returns a randomly selected tag. */
+tag_type
+tag_create_random(void)
+{
+ int x, y;
+ do {
+ uint16_t r = random_uint16();
+ x = r & (N_TAG_BITS - 1);
+ y = r >> (16 - LOG2_N_TAG_BITS);
+ } while (x == y);
+ return (1u << x) | (1u << y);
+}
+
+/* Returns a tag deterministically generated from 'seed'.
+ *
+ * 'seed' should have data in all of its bits; if it has data only in its
+ * low-order bits then the resulting tags will be poorly distributed. Use a
+ * hash function such as hash_lookup3() to generate 'seed' if necessary. */
+tag_type
+tag_create_deterministic(uint32_t seed)
+{
+ int x = seed & (N_TAG_BITS - 1);
+ int y = (seed >> LOG2_N_TAG_BITS) % 31;
+ y += y >= x;
+ return (1u << x) | (1u << y);
+}
+
+/* Initializes 'set' as an empty tag set. */
+void
+tag_set_init(struct tag_set *set)
+{
+ memset(set, 0, sizeof *set);
+}
+
+/* Adds 'tag' to 'set'. */
+void
+tag_set_add(struct tag_set *set, tag_type tag)
+{
+ if (tag) {
+ /* XXX We could do better by finding the set member to which we would
+ * add the fewest number of 1-bits. This would reduce the amount of
+ * ambiguity, since e.g. three 1-bits match 3 * 2 / 2 = 3 unique tags
+ * whereas four 1-bits match 4 * 3 / 2 = 6 unique tags. */
+ tag_type *t = &set->tags[set->n++ % TAG_SET_SIZE];
+ *t |= tag;
+ if (*t == TYPE_MAXIMUM(tag_type)) {
+ set->tags[0] = *t;
+ }
+
+ set->total |= tag;
+ }
+}
+
--- /dev/null
+/* Copyright (c) 2008 The Board of Trustees of The Leland Stanford
+ * Junior University
+ *
+ * We are making the OpenFlow specification and associated documentation
+ * (Software) available for public use and benefit with the expectation
+ * that others will use, modify and enhance the Software and contribute
+ * those enhancements back to the community. However, since we would
+ * like to make the Software available for broadest use, with as few
+ * restrictions as possible permission is hereby granted, free of
+ * charge, to any person obtaining a copy of this Software to deal in
+ * the Software under the copyrights without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ * The name and trademarks of copyright holder(s) may NOT be used in
+ * advertising or publicity pertaining to the Software or any
+ * derivatives without specific, written prior permission.
+ */
+
+#ifndef TAG_H
+#define TAG_H 1
+
+#include <assert.h>
+#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);
+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 */
projects / openvswitch / commitdiff