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/*
* BIRD Object Locks
*
* (c) 1999 Martin Mares <mj@ucw.cz>
*
* 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 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 doesn't
* use the resource until it's notified that it has acquired the lock.
*
* Object locks are represented by &object_lock which is 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 and interface.
*/
#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 &&
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(&l->waiters, &q->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) [%s]\n", l->type, (l->iface ? l->iface->name : "?"), l->addr, l->port, 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
};
/**
* 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)
{
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;
}
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