/* * BIRD Object Locks * * (c) 1999 Martin Mares * * Can be freely distributed and used under the terms of the GNU GPL. */ /** * DOC: Object locks * * The lock module provides a simple mechanism for avoiding conflicts between * various protocols which would like to use a single physical resource (for * example a network port). It would be easy to say that such collisions can * occur only when the user specifies an invalid configuration and therefore * he deserves to get what he has asked for, but unfortunately they can also * arise legitimately when the daemon is reconfigured and there exists (although * for a short time period only) an old protocol instance being shut down and a new one * willing to start up on the same interface. * * The solution is very simple: when any protocol wishes to use a network port * or some other non-shareable resource, it asks the core to lock it and it doesn't * use the resource until it's notified that it has acquired the lock. * * Object locks are represented by &object_lock structures which are in turn a * kind of resource. Lockable resources are uniquely determined by resource type * (%OBJLOCK_UDP for a UDP port etc.), IP address (usually a broadcast or * multicast address the port is bound to), port number, interface and optional * instance ID. */ #undef LOCAL_DEBUG #include "nest/bird.h" #include "lib/resource.h" #include "nest/locks.h" #include "nest/iface.h" static list olock_list; static event *olock_event; static inline int olock_same(struct object_lock *x, struct object_lock *y) { return x->type == y->type && x->iface == y->iface && x->port == y->port && x->inst == y->inst && ipa_equal(x->addr, y->addr); } static void olock_free(resource *r) { struct object_lock *q, *l = (struct object_lock *) r; node *n; DBG("olock: Freeing %p\n", l); switch (l->state) { case OLOCK_STATE_FREE: break; case OLOCK_STATE_LOCKED: case OLOCK_STATE_EVENT: rem_node(&l->n); n = HEAD(l->waiters); if (n->next) { DBG("olock: -> %p becomes locked\n", n); q = SKIP_BACK(struct object_lock, n, n); rem_node(n); add_tail_list(&q->waiters, &l->waiters); q->state = OLOCK_STATE_EVENT; add_head(&olock_list, n); ev_schedule(olock_event); } break; case OLOCK_STATE_WAITING: rem_node(&l->n); break; default: ASSERT(0); } } static void olock_dump(resource *r) { struct object_lock *l = (struct object_lock *) r; static char *olock_states[] = { "free", "locked", "waiting", "event" }; debug("(%d:%s:%I:%d:%d) [%s]\n", l->type, (l->iface ? l->iface->name : "?"), l->addr, l->port, l->inst, olock_states[l->state]); if (!EMPTY_LIST(l->waiters)) debug(" [wanted]\n"); } static struct resclass olock_class = { "ObjLock", sizeof(struct object_lock), olock_free, olock_dump, NULL }; /** * olock_new - create an object lock * @p: resource pool to create the lock in. * * The olock_new() function creates a new resource of type &object_lock * and returns a pointer to it. After filling in the structure, the caller * should call olock_acquire() to do the real locking. */ struct object_lock * olock_new(pool *p) { struct object_lock *l = ralloc(p, &olock_class); l->state = OLOCK_STATE_FREE; init_list(&l->waiters); return l; } /** * olock_acquire - acquire a lock * @l: the lock to acquire * * This function attempts to acquire exclusive access to the non-shareable * resource described by the lock @l. It returns immediately, but as soon * as the resource becomes available, it calls the hook() function set up * by the caller. * * When you want to release the resource, just rfree() the lock. */ void olock_acquire(struct object_lock *l) { node *n; struct object_lock *q; WALK_LIST(n, olock_list) { q = SKIP_BACK(struct object_lock, n, n); if (olock_same(q, l)) { l->state = OLOCK_STATE_WAITING; add_tail(&q->waiters, &l->n); DBG("olock: %p waits\n", l); return; } } DBG("olock: %p acquired immediately\n", l); l->state = OLOCK_STATE_EVENT; add_head(&olock_list, &l->n); ev_schedule(olock_event); } static void olock_run_event(void *unused UNUSED) { node *n; struct object_lock *q; DBG("olock: Processing events\n"); for(;;) { n = HEAD(olock_list); if (!n->next) break; q = SKIP_BACK(struct object_lock, n, n); if (q->state != OLOCK_STATE_EVENT) break; DBG("olock: %p locked\n", q); q->state = OLOCK_STATE_LOCKED; rem_node(&q->n); add_tail(&olock_list, &q->n); q->hook(q); } } /** * olock_init - initialize the object lock mechanism * * This function is called during BIRD startup. It initializes * all the internal data structures of the lock module. */ void olock_init(void) { DBG("olock: init\n"); init_list(&olock_list); olock_event = ev_new(&root_pool); olock_event->hook = olock_run_event; }