1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
|
/*
* 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 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(&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:%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;
}
|
