464 строки
14 KiB
C
464 строки
14 KiB
C
/*
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* INETPEER - A storage for permanent information about peers
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*
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* This source is covered by the GNU GPL, the same as all kernel sources.
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*
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* Authors: Andrey V. Savochkin <saw@msu.ru>
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*/
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#include <linux/module.h>
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#include <linux/types.h>
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#include <linux/slab.h>
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#include <linux/interrupt.h>
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#include <linux/spinlock.h>
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#include <linux/random.h>
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#include <linux/timer.h>
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#include <linux/time.h>
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#include <linux/kernel.h>
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#include <linux/mm.h>
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#include <linux/net.h>
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#include <net/ip.h>
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#include <net/inetpeer.h>
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/*
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* Theory of operations.
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* We keep one entry for each peer IP address. The nodes contains long-living
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* information about the peer which doesn't depend on routes.
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* At this moment this information consists only of ID field for the next
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* outgoing IP packet. This field is incremented with each packet as encoded
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* in inet_getid() function (include/net/inetpeer.h).
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* At the moment of writing this notes identifier of IP packets is generated
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* to be unpredictable using this code only for packets subjected
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* (actually or potentially) to defragmentation. I.e. DF packets less than
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* PMTU in size uses a constant ID and do not use this code (see
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* ip_select_ident() in include/net/ip.h).
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*
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* Route cache entries hold references to our nodes.
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* New cache entries get references via lookup by destination IP address in
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* the avl tree. The reference is grabbed only when it's needed i.e. only
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* when we try to output IP packet which needs an unpredictable ID (see
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* __ip_select_ident() in net/ipv4/route.c).
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* Nodes are removed only when reference counter goes to 0.
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* When it's happened the node may be removed when a sufficient amount of
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* time has been passed since its last use. The less-recently-used entry can
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* also be removed if the pool is overloaded i.e. if the total amount of
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* entries is greater-or-equal than the threshold.
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*
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* Node pool is organised as an AVL tree.
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* Such an implementation has been chosen not just for fun. It's a way to
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* prevent easy and efficient DoS attacks by creating hash collisions. A huge
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* amount of long living nodes in a single hash slot would significantly delay
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* lookups performed with disabled BHs.
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*
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* Serialisation issues.
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* 1. Nodes may appear in the tree only with the pool write lock held.
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* 2. Nodes may disappear from the tree only with the pool write lock held
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* AND reference count being 0.
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* 3. Nodes appears and disappears from unused node list only under
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* "inet_peer_unused_lock".
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* 4. Global variable peer_total is modified under the pool lock.
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* 5. struct inet_peer fields modification:
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* avl_left, avl_right, avl_parent, avl_height: pool lock
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* unused: unused node list lock
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* refcnt: atomically against modifications on other CPU;
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* usually under some other lock to prevent node disappearing
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* dtime: unused node list lock
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* v4daddr: unchangeable
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* ip_id_count: idlock
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*/
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/* Exported for inet_getid inline function. */
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DEFINE_SPINLOCK(inet_peer_idlock);
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static struct kmem_cache *peer_cachep __read_mostly;
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#define node_height(x) x->avl_height
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static struct inet_peer peer_fake_node = {
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.avl_left = &peer_fake_node,
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.avl_right = &peer_fake_node,
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.avl_height = 0
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};
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#define peer_avl_empty (&peer_fake_node)
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static struct inet_peer *peer_root = peer_avl_empty;
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static DEFINE_RWLOCK(peer_pool_lock);
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#define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */
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static int peer_total;
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/* Exported for sysctl_net_ipv4. */
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int inet_peer_threshold __read_mostly = 65536 + 128; /* start to throw entries more
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* aggressively at this stage */
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int inet_peer_minttl __read_mostly = 120 * HZ; /* TTL under high load: 120 sec */
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int inet_peer_maxttl __read_mostly = 10 * 60 * HZ; /* usual time to live: 10 min */
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int inet_peer_gc_mintime __read_mostly = 10 * HZ;
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int inet_peer_gc_maxtime __read_mostly = 120 * HZ;
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static LIST_HEAD(unused_peers);
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static DEFINE_SPINLOCK(inet_peer_unused_lock);
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static void peer_check_expire(unsigned long dummy);
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static DEFINE_TIMER(peer_periodic_timer, peer_check_expire, 0, 0);
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/* Called from ip_output.c:ip_init */
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void __init inet_initpeers(void)
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{
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struct sysinfo si;
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/* Use the straight interface to information about memory. */
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si_meminfo(&si);
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/* The values below were suggested by Alexey Kuznetsov
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* <kuznet@ms2.inr.ac.ru>. I don't have any opinion about the values
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* myself. --SAW
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*/
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if (si.totalram <= (32768*1024)/PAGE_SIZE)
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inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */
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if (si.totalram <= (16384*1024)/PAGE_SIZE)
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inet_peer_threshold >>= 1; /* about 512KB */
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if (si.totalram <= (8192*1024)/PAGE_SIZE)
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inet_peer_threshold >>= 2; /* about 128KB */
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peer_cachep = kmem_cache_create("inet_peer_cache",
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sizeof(struct inet_peer),
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0, SLAB_HWCACHE_ALIGN|SLAB_PANIC,
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NULL);
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/* All the timers, started at system startup tend
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to synchronize. Perturb it a bit.
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*/
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peer_periodic_timer.expires = jiffies
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+ net_random() % inet_peer_gc_maxtime
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+ inet_peer_gc_maxtime;
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add_timer(&peer_periodic_timer);
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}
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/* Called with or without local BH being disabled. */
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static void unlink_from_unused(struct inet_peer *p)
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{
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spin_lock_bh(&inet_peer_unused_lock);
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list_del_init(&p->unused);
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spin_unlock_bh(&inet_peer_unused_lock);
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}
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/*
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* Called with local BH disabled and the pool lock held.
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* _stack is known to be NULL or not at compile time,
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* so compiler will optimize the if (_stack) tests.
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*/
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#define lookup(_daddr,_stack) \
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({ \
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struct inet_peer *u, **v; \
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if (_stack != NULL) { \
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stackptr = _stack; \
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*stackptr++ = &peer_root; \
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} \
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for (u = peer_root; u != peer_avl_empty; ) { \
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if (_daddr == u->v4daddr) \
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break; \
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if ((__force __u32)_daddr < (__force __u32)u->v4daddr) \
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v = &u->avl_left; \
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else \
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v = &u->avl_right; \
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if (_stack != NULL) \
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*stackptr++ = v; \
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u = *v; \
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} \
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u; \
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})
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/* Called with local BH disabled and the pool write lock held. */
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#define lookup_rightempty(start) \
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({ \
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struct inet_peer *u, **v; \
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*stackptr++ = &start->avl_left; \
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v = &start->avl_left; \
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for (u = *v; u->avl_right != peer_avl_empty; ) { \
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v = &u->avl_right; \
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*stackptr++ = v; \
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u = *v; \
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} \
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u; \
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})
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/* Called with local BH disabled and the pool write lock held.
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* Variable names are the proof of operation correctness.
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* Look into mm/map_avl.c for more detail description of the ideas. */
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static void peer_avl_rebalance(struct inet_peer **stack[],
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struct inet_peer ***stackend)
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{
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struct inet_peer **nodep, *node, *l, *r;
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int lh, rh;
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while (stackend > stack) {
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nodep = *--stackend;
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node = *nodep;
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l = node->avl_left;
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r = node->avl_right;
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lh = node_height(l);
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rh = node_height(r);
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if (lh > rh + 1) { /* l: RH+2 */
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struct inet_peer *ll, *lr, *lrl, *lrr;
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int lrh;
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ll = l->avl_left;
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lr = l->avl_right;
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lrh = node_height(lr);
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if (lrh <= node_height(ll)) { /* ll: RH+1 */
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node->avl_left = lr; /* lr: RH or RH+1 */
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node->avl_right = r; /* r: RH */
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node->avl_height = lrh + 1; /* RH+1 or RH+2 */
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l->avl_left = ll; /* ll: RH+1 */
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l->avl_right = node; /* node: RH+1 or RH+2 */
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l->avl_height = node->avl_height + 1;
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*nodep = l;
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} else { /* ll: RH, lr: RH+1 */
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lrl = lr->avl_left; /* lrl: RH or RH-1 */
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lrr = lr->avl_right; /* lrr: RH or RH-1 */
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node->avl_left = lrr; /* lrr: RH or RH-1 */
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node->avl_right = r; /* r: RH */
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node->avl_height = rh + 1; /* node: RH+1 */
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l->avl_left = ll; /* ll: RH */
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l->avl_right = lrl; /* lrl: RH or RH-1 */
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l->avl_height = rh + 1; /* l: RH+1 */
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lr->avl_left = l; /* l: RH+1 */
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lr->avl_right = node; /* node: RH+1 */
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lr->avl_height = rh + 2;
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*nodep = lr;
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}
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} else if (rh > lh + 1) { /* r: LH+2 */
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struct inet_peer *rr, *rl, *rlr, *rll;
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int rlh;
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rr = r->avl_right;
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rl = r->avl_left;
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rlh = node_height(rl);
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if (rlh <= node_height(rr)) { /* rr: LH+1 */
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node->avl_right = rl; /* rl: LH or LH+1 */
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node->avl_left = l; /* l: LH */
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node->avl_height = rlh + 1; /* LH+1 or LH+2 */
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r->avl_right = rr; /* rr: LH+1 */
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r->avl_left = node; /* node: LH+1 or LH+2 */
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r->avl_height = node->avl_height + 1;
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*nodep = r;
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} else { /* rr: RH, rl: RH+1 */
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rlr = rl->avl_right; /* rlr: LH or LH-1 */
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rll = rl->avl_left; /* rll: LH or LH-1 */
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node->avl_right = rll; /* rll: LH or LH-1 */
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node->avl_left = l; /* l: LH */
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node->avl_height = lh + 1; /* node: LH+1 */
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r->avl_right = rr; /* rr: LH */
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r->avl_left = rlr; /* rlr: LH or LH-1 */
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r->avl_height = lh + 1; /* r: LH+1 */
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rl->avl_right = r; /* r: LH+1 */
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rl->avl_left = node; /* node: LH+1 */
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rl->avl_height = lh + 2;
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*nodep = rl;
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}
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} else {
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node->avl_height = (lh > rh ? lh : rh) + 1;
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}
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}
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}
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/* Called with local BH disabled and the pool write lock held. */
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#define link_to_pool(n) \
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do { \
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n->avl_height = 1; \
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n->avl_left = peer_avl_empty; \
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n->avl_right = peer_avl_empty; \
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**--stackptr = n; \
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peer_avl_rebalance(stack, stackptr); \
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} while(0)
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/* May be called with local BH enabled. */
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static void unlink_from_pool(struct inet_peer *p)
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{
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int do_free;
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do_free = 0;
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write_lock_bh(&peer_pool_lock);
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/* Check the reference counter. It was artificially incremented by 1
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* in cleanup() function to prevent sudden disappearing. If the
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* reference count is still 1 then the node is referenced only as `p'
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* here and from the pool. So under the exclusive pool lock it's safe
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* to remove the node and free it later. */
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if (atomic_read(&p->refcnt) == 1) {
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struct inet_peer **stack[PEER_MAXDEPTH];
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struct inet_peer ***stackptr, ***delp;
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if (lookup(p->v4daddr, stack) != p)
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BUG();
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delp = stackptr - 1; /* *delp[0] == p */
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if (p->avl_left == peer_avl_empty) {
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*delp[0] = p->avl_right;
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--stackptr;
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} else {
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/* look for a node to insert instead of p */
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struct inet_peer *t;
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t = lookup_rightempty(p);
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BUG_ON(*stackptr[-1] != t);
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**--stackptr = t->avl_left;
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/* t is removed, t->v4daddr > x->v4daddr for any
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* x in p->avl_left subtree.
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* Put t in the old place of p. */
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*delp[0] = t;
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t->avl_left = p->avl_left;
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t->avl_right = p->avl_right;
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t->avl_height = p->avl_height;
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BUG_ON(delp[1] != &p->avl_left);
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delp[1] = &t->avl_left; /* was &p->avl_left */
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}
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peer_avl_rebalance(stack, stackptr);
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peer_total--;
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do_free = 1;
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}
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write_unlock_bh(&peer_pool_lock);
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if (do_free)
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kmem_cache_free(peer_cachep, p);
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else
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/* The node is used again. Decrease the reference counter
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* back. The loop "cleanup -> unlink_from_unused
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* -> unlink_from_pool -> putpeer -> link_to_unused
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* -> cleanup (for the same node)"
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* doesn't really exist because the entry will have a
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* recent deletion time and will not be cleaned again soon. */
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inet_putpeer(p);
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}
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/* May be called with local BH enabled. */
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static int cleanup_once(unsigned long ttl)
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{
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struct inet_peer *p = NULL;
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/* Remove the first entry from the list of unused nodes. */
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spin_lock_bh(&inet_peer_unused_lock);
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if (!list_empty(&unused_peers)) {
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__u32 delta;
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p = list_first_entry(&unused_peers, struct inet_peer, unused);
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delta = (__u32)jiffies - p->dtime;
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if (delta < ttl) {
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/* Do not prune fresh entries. */
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spin_unlock_bh(&inet_peer_unused_lock);
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return -1;
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}
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list_del_init(&p->unused);
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/* Grab an extra reference to prevent node disappearing
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* before unlink_from_pool() call. */
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atomic_inc(&p->refcnt);
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}
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spin_unlock_bh(&inet_peer_unused_lock);
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if (p == NULL)
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/* It means that the total number of USED entries has
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* grown over inet_peer_threshold. It shouldn't really
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* happen because of entry limits in route cache. */
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return -1;
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unlink_from_pool(p);
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return 0;
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}
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/* Called with or without local BH being disabled. */
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struct inet_peer *inet_getpeer(__be32 daddr, int create)
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{
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struct inet_peer *p, *n;
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struct inet_peer **stack[PEER_MAXDEPTH], ***stackptr;
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/* Look up for the address quickly. */
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read_lock_bh(&peer_pool_lock);
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p = lookup(daddr, NULL);
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if (p != peer_avl_empty)
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atomic_inc(&p->refcnt);
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read_unlock_bh(&peer_pool_lock);
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if (p != peer_avl_empty) {
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/* The existing node has been found. */
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/* Remove the entry from unused list if it was there. */
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unlink_from_unused(p);
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return p;
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}
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if (!create)
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return NULL;
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/* Allocate the space outside the locked region. */
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n = kmem_cache_alloc(peer_cachep, GFP_ATOMIC);
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if (n == NULL)
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return NULL;
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n->v4daddr = daddr;
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atomic_set(&n->refcnt, 1);
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atomic_set(&n->rid, 0);
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n->ip_id_count = secure_ip_id(daddr);
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n->tcp_ts_stamp = 0;
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write_lock_bh(&peer_pool_lock);
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/* Check if an entry has suddenly appeared. */
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p = lookup(daddr, stack);
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if (p != peer_avl_empty)
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goto out_free;
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/* Link the node. */
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link_to_pool(n);
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INIT_LIST_HEAD(&n->unused);
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peer_total++;
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write_unlock_bh(&peer_pool_lock);
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if (peer_total >= inet_peer_threshold)
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/* Remove one less-recently-used entry. */
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cleanup_once(0);
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return n;
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out_free:
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/* The appropriate node is already in the pool. */
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atomic_inc(&p->refcnt);
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write_unlock_bh(&peer_pool_lock);
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/* Remove the entry from unused list if it was there. */
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unlink_from_unused(p);
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/* Free preallocated the preallocated node. */
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kmem_cache_free(peer_cachep, n);
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return p;
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}
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/* Called with local BH disabled. */
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static void peer_check_expire(unsigned long dummy)
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{
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unsigned long now = jiffies;
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int ttl;
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if (peer_total >= inet_peer_threshold)
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ttl = inet_peer_minttl;
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else
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ttl = inet_peer_maxttl
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- (inet_peer_maxttl - inet_peer_minttl) / HZ *
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peer_total / inet_peer_threshold * HZ;
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while (!cleanup_once(ttl)) {
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if (jiffies != now)
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break;
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}
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/* Trigger the timer after inet_peer_gc_mintime .. inet_peer_gc_maxtime
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* interval depending on the total number of entries (more entries,
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* less interval). */
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if (peer_total >= inet_peer_threshold)
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peer_periodic_timer.expires = jiffies + inet_peer_gc_mintime;
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else
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peer_periodic_timer.expires = jiffies
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+ inet_peer_gc_maxtime
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- (inet_peer_gc_maxtime - inet_peer_gc_mintime) / HZ *
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peer_total / inet_peer_threshold * HZ;
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add_timer(&peer_periodic_timer);
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}
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void inet_putpeer(struct inet_peer *p)
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{
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spin_lock_bh(&inet_peer_unused_lock);
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if (atomic_dec_and_test(&p->refcnt)) {
|
|
list_add_tail(&p->unused, &unused_peers);
|
|
p->dtime = (__u32)jiffies;
|
|
}
|
|
spin_unlock_bh(&inet_peer_unused_lock);
|
|
}
|