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/*
* INETPEER - A storage for permanent information about peers
*
* This source is covered by the GNU GPL, the same as all kernel sources.
*
* Version: $Id: inetpeer.c,v 1.7 2001/09/20 21:22:50 davem Exp $
*
* Authors: Andrey V. Savochkin <saw@msu.ru>
*/
#include <linux/module.h>
#include <linux/types.h>
#include <linux/slab.h>
#include <linux/interrupt.h>
#include <linux/spinlock.h>
#include <linux/random.h>
#include <linux/sched.h>
#include <linux/timer.h>
#include <linux/time.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/net.h>
#include <net/ip.h>
#include <net/inetpeer.h>
/*
* Theory of operations.
* We keep one entry for each peer IP address. The nodes contains long-living
* information about the peer which doesn't depend on routes.
* At this moment this information consists only of ID field for the next
* outgoing IP packet. This field is incremented with each packet as encoded
* in inet_getid() function (include/net/inetpeer.h).
* At the moment of writing this notes identifier of IP packets is generated
* to be unpredictable using this code only for packets subjected
* (actually or potentially) to defragmentation. I.e. DF packets less than
* PMTU in size uses a constant ID and do not use this code (see
* ip_select_ident() in include/net/ip.h).
*
* Route cache entries hold references to our nodes.
* New cache entries get references via lookup by destination IP address in
* the avl tree. The reference is grabbed only when it's needed i.e. only
* when we try to output IP packet which needs an unpredictable ID (see
* __ip_select_ident() in net/ipv4/route.c).
* Nodes are removed only when reference counter goes to 0.
* When it's happened the node may be removed when a sufficient amount of
* time has been passed since its last use. The less-recently-used entry can
* also be removed if the pool is overloaded i.e. if the total amount of
* entries is greater-or-equal than the threshold.
*
* Node pool is organised as an AVL tree.
* Such an implementation has been chosen not just for fun. It's a way to
* prevent easy and efficient DoS attacks by creating hash collisions. A huge
* amount of long living nodes in a single hash slot would significantly delay
* lookups performed with disabled BHs.
*
* Serialisation issues.
* 1. Nodes may appear in the tree only with the pool write lock held.
* 2. Nodes may disappear from the tree only with the pool write lock held
* AND reference count being 0.
* 3. Nodes appears and disappears from unused node list only under
* "inet_peer_unused_lock".
* 4. Global variable peer_total is modified under the pool lock.
* 5. struct inet_peer fields modification:
* avl_left, avl_right, avl_parent, avl_height: pool lock
* unused_next, unused_prevp: unused node list lock
* refcnt: atomically against modifications on other CPU;
* usually under some other lock to prevent node disappearing
* dtime: unused node list lock
* v4daddr: unchangeable
* ip_id_count: idlock
*/
/* Exported for inet_getid inline function. */
DEFINE_SPINLOCK(inet_peer_idlock);
static kmem_cache_t *peer_cachep __read_mostly;
#define node_height(x) x->avl_height
static struct inet_peer peer_fake_node = {
.avl_left = &peer_fake_node,
.avl_right = &peer_fake_node,
.avl_height = 0
};
#define peer_avl_empty (&peer_fake_node)
static struct inet_peer *peer_root = peer_avl_empty;
static DEFINE_RWLOCK(peer_pool_lock);
#define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */
static volatile int peer_total;
/* Exported for sysctl_net_ipv4. */
int inet_peer_threshold = 65536 + 128; /* start to throw entries more
* aggressively at this stage */
int inet_peer_minttl = 120 * HZ; /* TTL under high load: 120 sec */
int inet_peer_maxttl = 10 * 60 * HZ; /* usual time to live: 10 min */
static struct inet_peer *inet_peer_unused_head;
/* Exported for inet_putpeer inline function. */
struct inet_peer **inet_peer_unused_tailp = &inet_peer_unused_head;
DEFINE_SPINLOCK(inet_peer_unused_lock);
#define PEER_MAX_CLEANUP_WORK 30
static void peer_check_expire(unsigned long dummy);
static DEFINE_TIMER(peer_periodic_timer, peer_check_expire, 0, 0);
/* Exported for sysctl_net_ipv4. */
int inet_peer_gc_mintime = 10 * HZ,
inet_peer_gc_maxtime = 120 * HZ;
/* Called from ip_output.c:ip_init */
void __init inet_initpeers(void)
{
struct sysinfo si;
/* Use the straight interface to information about memory. */
si_meminfo(&si);
/* The values below were suggested by Alexey Kuznetsov
* <kuznet@ms2.inr.ac.ru>. I don't have any opinion about the values
* myself. --SAW
*/
if (si.totalram <= (32768*1024)/PAGE_SIZE)
inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */
if (si.totalram <= (16384*1024)/PAGE_SIZE)
inet_peer_threshold >>= 1; /* about 512KB */
if (si.totalram <= (8192*1024)/PAGE_SIZE)
inet_peer_threshold >>= 2; /* about 128KB */
peer_cachep = kmem_cache_create("inet_peer_cache",
sizeof(struct inet_peer),
0, SLAB_HWCACHE_ALIGN,
NULL, NULL);
if (!peer_cachep)
panic("cannot create inet_peer_cache");
/* All the timers, started at system startup tend
to synchronize. Perturb it a bit.
*/
peer_periodic_timer.expires = jiffies
+ net_random() % inet_peer_gc_maxtime
+ inet_peer_gc_maxtime;
add_timer(&peer_periodic_timer);
}
/* Called with or without local BH being disabled. */
static void unlink_from_unused(struct inet_peer *p)
{
spin_lock_bh(&inet_peer_unused_lock);
if (p->unused_prevp != NULL) {
/* On unused list. */
*p->unused_prevp = p->unused_next;
if (p->unused_next != NULL)
p->unused_next->unused_prevp = p->unused_prevp;
else
inet_peer_unused_tailp = p->unused_prevp;
p->unused_prevp = NULL; /* mark it as removed */
}
spin_unlock_bh(&inet_peer_unused_lock);
}
/* Called with local BH disabled and the pool lock held. */
#define lookup(daddr) \
({ \
struct inet_peer *u, **v; \
stackptr = stack; \
*stackptr++ = &peer_root; \
for (u = peer_root; u != peer_avl_empty; ) { \
if (daddr == u->v4daddr) \
break; \
if (daddr < u->v4daddr) \
v = &u->avl_left; \
else \
v = &u->avl_right; \
*stackptr++ = v; \
u = *v; \
} \
u; \
})
/* Called with local BH disabled and the pool write lock held. */
#define lookup_rightempty(start) \
({ \
struct inet_peer *u, **v; \
*stackptr++ = &start->avl_left; \
v = &start->avl_left; \
for (u = *v; u->avl_right != peer_avl_empty; ) { \
v = &u->avl_right; \
*stackptr++ = v; \
u = *v; \
} \
u; \
})
/* Called with local BH disabled and the pool write lock held.
* Variable names are the proof of operation correctness.
* Look into mm/map_avl.c for more detail description of the ideas. */
static void peer_avl_rebalance(struct inet_peer **stack[],
struct inet_peer ***stackend)
{
struct inet_peer **nodep, *node, *l, *r;
int lh, rh;
while (stackend > stack) {
nodep = *--stackend;
node = *nodep;
l = node->avl_left;
r = node->avl_right;
lh = node_height(l);
rh = node_height(r);
if (lh > rh + 1) { /* l: RH+2 */
struct inet_peer *ll, *lr, *lrl, *lrr;
int lrh;
ll = l->avl_left;
lr = l->avl_right;
lrh = node_height(lr);
if (lrh <= node_height(ll)) { /* ll: RH+1 */
node->avl_left = lr; /* lr: RH or RH+1 */
node->avl_right = r; /* r: RH */
node->avl_height = lrh + 1; /* RH+1 or RH+2 */
l->avl_left = ll; /* ll: RH+1 */
l->avl_right = node; /* node: RH+1 or RH+2 */
l->avl_height = node->avl_height + 1;
*nodep = l;
} else { /* ll: RH, lr: RH+1 */
lrl = lr->avl_left; /* lrl: RH or RH-1 */
lrr = lr->avl_right; /* lrr: RH or RH-1 */
node->avl_left = lrr; /* lrr: RH or RH-1 */
node->avl_right = r; /* r: RH */
node->avl_height = rh + 1; /* node: RH+1 */
l->avl_left = ll; /* ll: RH */
l->avl_right = lrl; /* lrl: RH or RH-1 */
l->avl_height = rh + 1; /* l: RH+1 */
lr->avl_left = l; /* l: RH+1 */
lr->avl_right = node; /* node: RH+1 */
lr->avl_height = rh + 2;
*nodep = lr;
}
} else if (rh > lh + 1) { /* r: LH+2 */
struct inet_peer *rr, *rl, *rlr, *rll;
int rlh;
rr = r->avl_right;
rl = r->avl_left;
rlh = node_height(rl);
if (rlh <= node_height(rr)) { /* rr: LH+1 */
node->avl_right = rl; /* rl: LH or LH+1 */
node->avl_left = l; /* l: LH */
node->avl_height = rlh + 1; /* LH+1 or LH+2 */
r->avl_right = rr; /* rr: LH+1 */
r->avl_left = node; /* node: LH+1 or LH+2 */
r->avl_height = node->avl_height + 1;
*nodep = r;
} else { /* rr: RH, rl: RH+1 */
rlr = rl->avl_right; /* rlr: LH or LH-1 */
rll = rl->avl_left; /* rll: LH or LH-1 */
node->avl_right = rll; /* rll: LH or LH-1 */
node->avl_left = l; /* l: LH */
node->avl_height = lh + 1; /* node: LH+1 */
r->avl_right = rr; /* rr: LH */
r->avl_left = rlr; /* rlr: LH or LH-1 */
r->avl_height = lh + 1; /* r: LH+1 */
rl->avl_right = r; /* r: LH+1 */
rl->avl_left = node; /* node: LH+1 */
rl->avl_height = lh + 2;
*nodep =<
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