ovsdb/server.c

   1 /* Copyright (c) 2011, 2012 Nicira, Inc.
   2  *
   3  * Licensed under the Apache License, Version 2.0 (the "License");
   4  * you may not use this file except in compliance with the License.
   5  * You may obtain a copy of the License at:
   6  *
   7  *     http://www.apache.org/licenses/LICENSE-2.0
   8  *
   9  * Unless required by applicable law or agreed to in writing, software
  10  * distributed under the License is distributed on an "AS IS" BASIS,
  11  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  12  * See the License for the specific language governing permissions and
  13  * limitations under the License.
  14  */
  15
  16 #include <config.h>
  17
  18 #include "server.h"
  19
  20 #include "hash.h"
  21 #include "ovsdb.h"
  22
  23 /* Initializes 'session' as a session within 'server'. */
  24 void
  25 ovsdb_session_init(struct ovsdb_session *session, struct ovsdb_server *server)
  26 {
  27     session->server = server;
  28     list_init(&session->completions);
  29     hmap_init(&session->waiters);
  30 }
  31
  32 /* Destroys 'session'. */
  33 void
  34 ovsdb_session_destroy(struct ovsdb_session *session)
  35 {
  36     ovs_assert(hmap_is_empty(&session->waiters));
  37     hmap_destroy(&session->waiters);
  38 }
  39
  40 /* Searches 'session' for an ovsdb_lock_waiter named 'lock_name' and returns
  41  * it if it finds one, otherwise NULL. */
  42 struct ovsdb_lock_waiter *
  43 ovsdb_session_get_lock_waiter(const struct ovsdb_session *session,
  44                               const char *lock_name)
  45 {
  46     struct ovsdb_lock_waiter *waiter;
  47
  48     HMAP_FOR_EACH_WITH_HASH (waiter, session_node, hash_string(lock_name, 0),
  49                              &session->waiters) {
  50         if (!strcmp(lock_name, waiter->lock_name)) {
  51             return waiter;
  52         }
  53     }
  54     return NULL;
  55 }
  56
  57 /* Returns the waiter that owns 'lock'.
  58  *
  59  * A lock always has an owner, so this function will never return NULL. */
  60 struct ovsdb_lock_waiter *
  61 ovsdb_lock_get_owner(const struct ovsdb_lock *lock)
  62 {
  63     return CONTAINER_OF(list_front(&lock->waiters),
  64                         struct ovsdb_lock_waiter, lock_node);
  65 }
  66
  67 /* Removes 'waiter' from its lock's list.  This means that, if 'waiter' was
  68  * formerly the owner of its lock, then it no longer owns it.
  69  *
  70  * Returns the session that now owns 'waiter'.  This is NULL if 'waiter' was
  71  * the lock's owner and no other sessions were waiting for the lock.  In this
  72  * case, the lock has been destroyed, so the caller must be sure not to refer
  73  * to it again.  A nonnull return value reflects a change in the lock's
  74  * ownership if and only if 'waiter' formerly owned the lock. */
  75 struct ovsdb_session *
  76 ovsdb_lock_waiter_remove(struct ovsdb_lock_waiter *waiter)
  77 {
  78     struct ovsdb_lock *lock = waiter->lock;
  79
  80     list_remove(&waiter->lock_node);
  81     waiter->lock = NULL;
  82
  83     if (list_is_empty(&lock->waiters)) {
  84         hmap_remove(&lock->server->locks, &lock->hmap_node);
  85         free(lock->name);
  86         free(lock);
  87         return NULL;
  88     }
  89
  90     return ovsdb_lock_get_owner(lock)->session;
  91 }
  92
  93 /* Destroys 'waiter', which must have already been removed from its lock's
  94  * waiting list with ovsdb_lock_waiter_remove().
  95  *
  96  * Removing and destroying locks are decoupled because a lock initially created
  97  * by the "steal" request, that is later stolen by another client, remains in
  98  * the database session until the database client sends an "unlock" request. */
  99 void
 100 ovsdb_lock_waiter_destroy(struct ovsdb_lock_waiter *waiter)
 101 {
 102     ovs_assert(!waiter->lock);
 103     hmap_remove(&waiter->session->waiters, &waiter->session_node);
 104     free(waiter->lock_name);
 105     free(waiter);
 106 }
 107
 108 /* Returns true if 'waiter' owns its associated lock. */
 109 bool
 110 ovsdb_lock_waiter_is_owner(const struct ovsdb_lock_waiter *waiter)
 111 {
 112     return waiter->lock && waiter == ovsdb_lock_get_owner(waiter->lock);
 113 }
 114
 115 /* Initializes 'server'.
 116  *
 117  * The caller must call ovsdb_server_add_db() for each database to which
 118  * 'server' should provide access. */
 119 void
 120 ovsdb_server_init(struct ovsdb_server *server)
 121 {
 122     shash_init(&server->dbs);
 123     hmap_init(&server->locks);
 124 }
 125
 126 /* Adds 'db' to the set of databases served out by 'server'.  Returns true if
 127  * successful, false if 'db''s name is the same as some database already in
 128  * 'server'. */
 129 bool
 130 ovsdb_server_add_db(struct ovsdb_server *server, struct ovsdb *db)
 131 {
 132     return shash_add_once(&server->dbs, db->schema->name, db);
 133 }
 134
 135 /* Destroys 'server'. */
 136 void
 137 ovsdb_server_destroy(struct ovsdb_server *server)
 138 {
 139     shash_destroy(&server->dbs);
 140     hmap_destroy(&server->locks);
 141 }
 142
 143 static struct ovsdb_lock *
 144 ovsdb_server_create_lock__(struct ovsdb_server *server, const char *lock_name,
 145                            uint32_t hash)
 146 {
 147     struct ovsdb_lock *lock;
 148
 149     HMAP_FOR_EACH_WITH_HASH (lock, hmap_node, hash, &server->locks) {
 150         if (!strcmp(lock->name, lock_name)) {
 151             return lock;
 152         }
 153     }
 154
 155     lock = xzalloc(sizeof *lock);
 156     lock->server = server;
 157     lock->name = xstrdup(lock_name);
 158     hmap_insert(&server->locks, &lock->hmap_node, hash);
 159     list_init(&lock->waiters);
 160
 161     return lock;
 162 }
 163
 164 /* Attempts to acquire the lock named 'lock_name' for 'session' within
 165  * 'server'.  Returns the new lock waiter.
 166  *
 167  * If 'mode' is OVSDB_LOCK_STEAL, then the new lock waiter is always the owner
 168  * of the lock.  '*victimp' receives the session of the previous owner or NULL
 169  * if the lock was previously unowned.  (If the victim itself originally
 170  * obtained the lock through a "steal" operation, then this function also
 171  * removes the victim from the lock's waiting list.)
 172  *
 173  * If 'mode' is OVSDB_LOCK_WAIT, then the new lock waiter is the owner of the
 174  * lock only if this lock had no existing owner.  '*victimp' is set to NULL. */
 175 struct ovsdb_lock_waiter *
 176 ovsdb_server_lock(struct ovsdb_server *server,
 177                   struct ovsdb_session *session,
 178                   const char *lock_name,
 179                   enum ovsdb_lock_mode mode,
 180                   struct ovsdb_session **victimp)
 181 {
 182     uint32_t hash = hash_string(lock_name, 0);
 183     struct ovsdb_lock_waiter *waiter, *victim;
 184     struct ovsdb_lock *lock;
 185
 186     lock = ovsdb_server_create_lock__(server, lock_name, hash);
 187     victim = (mode == OVSDB_LOCK_STEAL && !list_is_empty(&lock->waiters)
 188               ? ovsdb_lock_get_owner(lock)
 189               : NULL);
 190
 191     waiter = xmalloc(sizeof *waiter);
 192     waiter->mode = mode;
 193     waiter->lock_name = xstrdup(lock_name);
 194     waiter->lock = lock;
 195     if (mode == OVSDB_LOCK_STEAL) {
 196         list_push_front(&lock->waiters, &waiter->lock_node);
 197     } else {
 198         list_push_back(&lock->waiters, &waiter->lock_node);
 199     }
 200     waiter->session = session;
 201     hmap_insert(&waiter->session->waiters, &waiter->session_node, hash);
 202
 203     if (victim && victim->mode == OVSDB_LOCK_STEAL) {
 204         ovsdb_lock_waiter_remove(victim);
 205     }
 206     *victimp = victim ? victim->session : NULL;
 207
 208     return waiter;
 209 }