text: /*
   * Copyright (c) 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2017 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 CLASSIFIER_H
  #define CLASSIFIER_H 1
  
  /* Flow classifier.
   *
   *
   * What?
   * =====
   *
   * A flow classifier holds any number of "rules", each of which specifies
   * values to match for some fields or subfields and a priority.  Each OpenFlow
   * table is implemented as a flow classifier.
   *
   * The classifier has two primary design goals.  The first is obvious: given a
   * set of packet headers, as quickly as possible find the highest-priority rule
   * that matches those headers.  The following section describes the second
   * goal.
   *
   *
   * "Un-wildcarding"
   * ================
   *
   * A primary goal of the flow classifier is to produce, as a side effect of a
   * packet lookup, a wildcard mask that indicates which bits of the packet
   * headers were essential to the classification result.  Ideally, a 1-bit in
   * any position of this mask means that, if the corresponding bit in the packet
   * header were flipped, then the classification result might change.  A 0-bit
   * means that changing the packet header bit would have no effect.  Thus, the
   * wildcarded bits are the ones that played no role in the classification
   * decision.
   *
   * Such a wildcard mask is useful with datapaths that support installing flows
   * that wildcard fields or subfields.  If an OpenFlow lookup for a TCP flow
   * does not actually look at the TCP source or destination ports, for example,
   * then the switch may install into the datapath a flow that wildcards the port
   * numbers, which in turn allows the datapath to handle packets that arrive for
   * other TCP source or destination ports without additional help from
   * ovs-vswitchd.  This is useful for the Open vSwitch software and,
   * potentially, for ASIC-based switches as well.
   *
   * Some properties of the wildcard mask:
   *
   *     - "False 1-bits" are acceptable, that is, setting a bit in the wildcard
   *       mask to 1 will never cause a packet to be forwarded the wrong way.
   *       As a corollary, a wildcard mask composed of all 1-bits will always
   *       yield correct (but often needlessly inefficient) behavior.
   *
   *     - "False 0-bits" can cause problems, so they must be avoided.  In the
   *       extreme case, a mask of all 0-bits is only correct if the classifier
   *       contains only a single flow that matches all packets.
   *
   *     - 0-bits are desirable because they allow the datapath to act more
   *       autonomously, relying less on ovs-vswitchd to process flow setups,
   *       thereby improving performance.
   *
   *     - We don't know a good way to generate wildcard masks with the maximum
   *       (correct) number of 0-bits.  We use various approximations, described
   *       in later sections.
   *
   *     - Wildcard masks for lookups in a given classifier yield a
   *       non-overlapping set of rules.  More specifically:
   *
   *       Consider an classifier C1 filled with an arbitrary collection of rules
   *       and an empty classifier C2.  Now take a set of packet headers H and
   *       look it up in C1, yielding a highest-priority matching rule R1 and
   *       wildcard mask M.  Form a new classifier rule R2 out of packet headers
   *       H and mask M, and add R2 to C2 with a fixed priority.  If one were to
   *       do this for every possible set of packet headers H, then this
   *       process would not attempt to add any overlapping rules to C2, that is,
   *       any packet lookup using the rules generated by this process matches at
   *       most one rule in C2.
   *
   * During the lookup process, the classifier starts out with a wildcard mask
   * that is all 0-bits, that is, fully wildcarded.  As lookup proceeds, each
   * step tends to add constraints to the wildcard mask, that is, change
   * wildcarded 0-bits into exact-match 1-bits.  We call this "un-wildcarding".
   * A lookup step that examines a particular field must un-wildcard that field.
   * In general, un-wildcarding is necessary for correctness but undesirable for
   * performance.
   *
   *
   * Basic Classifier Design
   * =======================
   *
   * Suppose that all the rules in a classifier had the same form.  For example,
   * suppose that they all matched on the source and destination Ethernet address
   * and wildcarded all the other fields.  Then the obvious way to implement a
   * classifier would be a hash table on the source and destination Ethernet
   * addresses.  If new classification rules came along with a different form,
   * you could add a second hash table that hashed on the fields matched in those
   * rules.  With two hash tables, you look up a given flow in each hash table.
   * If there are no matches, the classifier didn't contain a match; if you find
   * a match in one of them, that's the result; if you find a match in both of
   * them, then the result is the rule with the higher priority.
   *
   * This is how the classifier works.  In a "struct classifier", each form of
   * "struct cls_rule" present (based on its ->match.mask) goes into a separate
   * "struct cls_subtable".  A lookup does a hash lookup in every "struct
   * cls_subtable" in the classifier and tracks the highest-priority match that
   * it finds.  The subtables are kept in a descending priority order according
   * to the highest priority rule in each subtable, which allows lookup to skip
   * over subtables that can't possibly have a higher-priority match than already
   * found.  Eliminating lookups through priority ordering aids both classifier
   * primary design goals: skipping lookups saves time and avoids un-wildcarding
   * fields that those lookups would have examined.
   *
   * One detail: a classifier can contain multiple rules that are identical other
   * than their priority.  When this happens, only the highest priority rule out
   * of a group of otherwise identical rules is stored directly in the "struct
   * cls_subtable", with the other almost-identical rules chained off a linked
   * list inside that highest-priority rule.
   *
   * The following sub-sections describe various optimizations over this simple
   * approach.
   *
   *
   * Staged Lookup (Wildcard Optimization)
   * -------------------------------------
   *
   * Subtable lookup is performed in ranges defined for struct flow, starting
   * from metadata (registers, in_port, etc.), then L2 header, L3, and finally
   * L4 ports.  Whenever it is found that there are no matches in the current
   * subtable, the rest of the subtable can be skipped.
   *
   * Staged lookup does not reduce lookup time, and it may increase it, because
   * it changes a single hash table lookup into multiple hash table lookups.
   * It reduces un-wildcarding significantly in important use cases.
   *
   *
   * Prefix Tracking (Wildcard Optimization)
   * ---------------------------------------
   *
   * Classifier uses prefix trees ("tries") for tracking the used
   * address space, enabling skipping classifier tables containing
   * longer masks than necessary for the given address.  This reduces
   * un-wildcarding for datapath flows in parts of the address space
   * without host routes, but consulting extra data structures (the
   * tries) may slightly increase lookup time.
   *
   * Trie lookup is interwoven with staged lookup, so that a trie is
   * searched only when the configured trie field becomes relevant for
   * the lookup.  The trie lookup results are retained so that each trie
   * is checked at most once for each classifier lookup.
   *
   * This implementation tracks the number of rules at each address
   * prefix for the whole classifier.  More aggressive table skipping
   * would be possible by maintaining lists of tables that have prefixes
   * at the lengths encountered on tree traversal, or by maintaining
   * separate tries for subsets of rules separated by metadata fields.
   *
   * Prefix tracking is configured via OVSDB "Flow_Table" table,
   * "fieldspec" column.  "fieldspec" is a string map where a "prefix"
   * key tells which fields should be used for prefix tracking.  The
   * value of the "prefix" key is a comma separated list of field names.
   *
   * There is a maximum number of fields that can be enabled for any one
   * flow table.  Currently this limit is 3.
   *
   *
   * Partitioning (Lookup Time and Wildcard Optimization)
   * ----------------------------------------------------
   *
   * Suppose that a given classifier is being used to handle multiple stages in a
   * pipeline using "resubmit", with metadata (that is, the OpenFlow 1.1+ field
   * named "metadata") distinguishing between the different stages.  For example,
   * metadata value 1 might identify ingress rules, metadata value 2 might
   * identify ACLs, and metadata value 3 might identify egress rules.  Such a
   * classifier is essentially partitioned into multiple sub-classifiers on the
   * basis of the metadata value.
   *
   * The classifier has a special optimization to speed up matching in this
   * scenario:
   *
   *     - Each cls_subtable that matches on metadata gets a tag derived from the
   *       subtable's mask, so that it is likely that each subtable has a unique
   *       tag.  (Duplicate tags have a performance cost but do not affect
   *       correctness.)
   *
   *     - For each metadata value matched by any cls_rule, the classifier
   *       constructs a "struct cls_partition" indexed by the metadata value.
   *       The cls_partition has a 'tags' member whose value is the bitwise-OR of
   *       the tags of each cls_subtable that contains any rule that matches on
   *       the cls_partition's metadata value.  In other words, struct
   *       cls_partition associates metadata values with subtables that need to
   *       be checked with flows with that specific metadata value.
   *
   * Thus, a flow lookup can start by looking up the partition associated with
   * the flow's metadata, and then skip over any cls_subtable whose 'tag' does
   * not intersect the partition's 'tags'.  (The flow must also be looked up in
   * any cls_subtable that doesn't match on metadata.  We handle that by giving
   * any such cls_subtable TAG_ALL as its 'tags' so that it matches any tag.)
   *
   * Partitioning saves lookup time by reducing the number of subtable lookups.
   * Each eliminated subtable lookup also reduces the amount of un-wildcarding.
   *
   *
   * Classifier Versioning
   * =====================
   *
   * Classifier lookups are always done in a specific classifier version, where
   * a version is defined to be a natural number.
   *
   * When a new rule is added to a classifier, it is set to become visible in a
   * specific version.  If the version number used at insert time is larger than
   * any version number currently used in lookups, the new rule is said to be
   * invisible to lookups.  This means that lookups won't find the rule, but the
   * rule is immediately available to classifier iterations.
   *
   * Similarly, a rule can be marked as to be deleted in a future version.  To
   * delete a rule in a way to not remove the rule before all ongoing lookups are
   * finished, the rule should be made invisible in a specific version number.
   * Then, when all the lookups use a later version number, the rule can be
   * actually removed from the classifier.
   *
   * Classifiers can hold duplicate rules (rules with the same match criteria and
   * priority) when at most one of these duplicates is visible in any given
   * lookup version.  The caller responsible for classifier modifications must
   * maintain this invariant.
   *
   * The classifier supports versioning for two reasons:
   *
   *     1. Support for versioned modifications makes it possible to perform an
   *        arbitrary series of classifier changes as one atomic transaction,
   *        where intermediate versions of the classifier are not visible to any
   *        lookups.  Also, when a rule is added for a future version, or marked
   *        for removal after the current version, such modifications can be
   *        reverted without any visible effects to any of the current lookups.
   *
   *     2. Performance: Adding (or deleting) a large set of rules can, in
   *        pathological cases, have a cost proportional to the number of rules
   *        already in the classifier.  When multiple rules are being added (or
   *        deleted) in one go, though, this pathological case cost can be
   *        typically avoided, as long as it is OK for any new rules to be
   *        invisible until the batch change is complete.
   *
   * Note that the classifier_replace() function replaces a rule immediately, and
   * is therefore not safe to use with versioning.  It is still available for the
   * users that do not use versioning.
   *
   *
   * Deferred Publication
   * ====================
   *
   * Removing large number of rules from classifier can be costly, as the
   * supporting data structures are teared down, in many cases just to be
   * re-instantiated right after.  In the worst case, as when each rule has a
   * different match pattern (mask), the maintenance of the match patterns can
   * have cost O(N^2), where N is the number of different match patterns.  To
   * alleviate this, the classifier supports a "deferred mode", in which changes
   * in internal data structures needed for future version lookups may not be
   * fully computed yet.  The computation is finalized when the deferred mode is
   * turned off.
   *
   * This feature can be used with versioning such that all changes to future
   * versions are made in the deferred mode.  Then, right before making the new
   * version visible to lookups, the deferred mode is turned off so that all the
   * data structures are ready for lookups with the new version number.
   *
   * To use deferred publication, first call classifier_defer().  Then, modify
   * the classifier via additions (classifier_insert() with a specific, future
   * version number) and deletions (use cls_rule_make_removable_after_version()).
   * Then call classifier_publish(), and after that, announce the new version
   * number to be used in lookups.
   *
   *
   * Thread-safety
   * =============
   *
   * The classifier may safely be accessed by many reader threads concurrently
   * and by a single writer, or by multiple writers when they guarantee mutually
   * exclusive access to classifier modifications.
   *
   * Since the classifier rules are RCU protected, the rule destruction after
   * removal from the classifier must be RCU postponed.  Also, when versioning is
   * used, the rule removal itself needs to be typically RCU postponed.  In this
   * case the rule destruction is doubly RCU postponed, i.e., the second
   * ovsrcu_postpone() call to destruct the rule is called from the first RCU
   * callback that removes the rule.
   *
   * Rules that have never been visible to lookups are an exception to the above
   * rule.  Such rules can be removed immediately, but their destruction must
   * still be RCU postponed, as the rule's visibility attribute may be examined
   * parallel to the rule's removal. */
  
  #include "cmap.h"
  #include "openvswitch/match.h"
  #include "openvswitch/meta-flow.h"
  #include "pvector.h"
  #include "rculist.h"
  #include "openvswitch/type-props.h"
  #include "versions.h"
  
  #ifdef __cplusplus
  extern "C" {
  #endif
  
  /* Classifier internal data structures. */
  struct cls_subtable;
  struct cls_match;
  
  struct trie_node;
  typedef OVSRCU_TYPE(struct trie_node *) rcu_trie_ptr;
  
  /* Prefix trie for a 'field' */
  struct cls_trie {
      const struct mf_field *field; /* Trie field, or NULL. */
      rcu_trie_ptr root;            /* NULL if none. */
  };
  
  enum {
      CLS_MAX_INDICES = 3,   /* Maximum number of lookup indices per subtable. */
      CLS_MAX_TRIES = 3      /* Maximum number of prefix trees per classifier. */
  };
  
  /* A flow classifier. */
  struct classifier {
      int n_rules;                    /* Total number of rules. */
      uint8_t n_flow_segments;
      uint8_t flow_segments[CLS_MAX_INDICES]; /* Flow segment boundaries to use
                                               * for staged lookup. */
      struct cmap subtables_map;      /* Contains "struct cls_subtable"s.  */
      struct pvector subtables;
      struct cmap partitions;         /* Contains "struct cls_partition"s. */
      struct cls_trie tries[CLS_MAX_TRIES]; /* Prefix tries. */
      unsigned int n_tries;
      bool publish;                   /* Make changes visible to lookups? */
  };
  
  struct cls_conjunction {
      uint32_t id;
      uint8_t clause;
      uint8_t n_clauses;
  };
  
  /* A rule to be inserted to the classifier. */
  struct cls_rule {
      struct rculist node;          /* In struct cls_subtable 'rules_list'. */
      const int priority;           /* Larger numbers are higher priorities. */
      OVSRCU_TYPE(struct cls_match *) cls_match;  /* NULL if not in a
                                                   * classifier. */
      const struct minimatch match; /* Matching rule. */
  };
  
  /* Constructor/destructor.  Must run single-threaded. */
  void classifier_init(struct classifier *, const uint8_t *flow_segments);
  void classifier_destroy(struct classifier *);
  
  /* Modifiers.  Caller MUST exclude concurrent calls from other threads. */
  bool classifier_set_prefix_fields(struct classifier *,
                                    const enum mf_field_id *trie_fields,
                                    unsigned int n_trie_fields);
  
  void cls_rule_init(struct cls_rule *, const struct match *, int priority);
  void cls_rule_init_from_minimatch(struct cls_rule *, const struct minimatch *,
                                    int priority);
  void cls_rule_clone(struct cls_rule *, const struct cls_rule *);
  void cls_rule_move(struct cls_rule *dst, struct cls_rule *src);
  void cls_rule_destroy(struct cls_rule *);
  
  void cls_rule_set_conjunctions(struct cls_rule *,
                                 const struct cls_conjunction *, size_t n);
  void cls_rule_make_invisible_in_version(const struct cls_rule *,
                                          ovs_version_t);
  void cls_rule_restore_visibility(const struct cls_rule *);
  
  void classifier_insert(struct classifier *, const struct cls_rule *,
                         ovs_version_t, const struct cls_conjunction *,
                         size_t n_conjunctions);
  const struct cls_rule *classifier_replace(struct classifier *,
                                            const struct cls_rule *,
                                            ovs_version_t,
                                            const struct cls_conjunction *,
                                            size_t n_conjunctions);
  bool classifier_remove(struct classifier *, const struct cls_rule *);
  void classifier_remove_assert(struct classifier *, const struct cls_rule *);
  static inline void classifier_defer(struct classifier *);
  static inline void classifier_publish(struct classifier *);
  
  /* Lookups.  These are RCU protected and may run concurrently with modifiers
   * and each other. */
  const struct cls_rule *classifier_lookup(const struct classifier *,
                                           ovs_version_t, struct flow *,
                                           struct flow_wildcards *);
  bool classifier_rule_overlaps(const struct classifier *,
                                const struct cls_rule *, ovs_version_t);
  const struct cls_rule *classifier_find_rule_exactly(const struct classifier *,
                                                      const struct cls_rule *,
                                                      ovs_version_t);
  const struct cls_rule *classifier_find_match_exactly(const struct classifier *,
                                                       const struct match *,
                                                       int priority,
                                                       ovs_version_t);
  const struct cls_rule *classifier_find_minimatch_exactly(
      const struct classifier *, const struct minimatch *,
      int priority, ovs_version_t);
  
  bool classifier_is_empty(const struct classifier *);
  int classifier_count(const struct classifier *);
  
  /* Classifier rule properties.  These are RCU protected and may run
   * concurrently with modifiers and each other. */
  bool cls_rule_equal(const struct cls_rule *, const struct cls_rule *);
  void cls_rule_format(const struct cls_rule *, const struct tun_table *,
                       const struct ofputil_port_map *, struct ds *);
  bool cls_rule_is_catchall(const struct cls_rule *);
  bool cls_rule_is_loose_match(const struct cls_rule *rule,
                               const struct minimatch *criteria);
  bool cls_rule_visible_in_version(const struct cls_rule *, ovs_version_t);
  
  /* Iteration.
   *
   * Iteration is lockless and RCU-protected.  Concurrent threads may perform all
   * kinds of concurrent modifications without ruining the iteration.  Obviously,
   * any modifications may or may not be visible to the concurrent iterator, but
   * all the rules not deleted are visited by the iteration.  The iterating
   * thread may also modify the classifier rules itself.
   *
   * 'TARGET' iteration only iterates rules matching the 'TARGET' criteria.
   * Rather than looping through all the rules and skipping ones that can't
   * match, 'TARGET' iteration skips whole subtables, if the 'TARGET' happens to
   * be more specific than the subtable. */
  struct cls_cursor {
      const struct classifier *cls;
      const struct cls_subtable *subtable;
      const struct cls_rule *target;
      ovs_version_t version;   /* Version to iterate. */
      struct pvector_cursor subtables;
      const struct cls_rule *rule;
  };
  
  struct cls_cursor cls_cursor_start(const struct classifier *,
                                     const struct cls_rule *target,
                                     ovs_version_t);
  void cls_cursor_advance(struct cls_cursor *);
  
  #define CLS_FOR_EACH(RULE, MEMBER, CLS)             \
      CLS_FOR_EACH_TARGET(RULE, MEMBER, CLS, NULL, OVS_VERSION_MAX)
  #define CLS_FOR_EACH_TARGET(RULE, MEMBER, CLS, TARGET, VERSION)         \
      for (struct cls_cursor cursor__ = cls_cursor_start(CLS, TARGET, VERSION); \
           (cursor__.rule                                                 \
            ? (INIT_CONTAINER(RULE, cursor__.rule, MEMBER),               \
               cls_cursor_advance(&cursor__),                             \
               true)                                                      \
            : false);                                                     \
          )
  
  
  static inline void
  classifier_defer(struct classifier *cls)
  {
      cls->publish = false;
  }
  
  static inline void
  classifier_publish(struct classifier *cls)
  {
      cls->publish = true;
      pvector_publish(&cls->subtables);
  }
  
  #ifdef __cplusplus
  }
  #endif
  #endif /* classifier.h */
  