litmus-rt.git - The LITMUS^RT kernel.

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Diffstat (limited to 'drivers/rtc/class.c')

0 files changed, 0 insertions, 0 deletions

/* * INETPEER - A storage for permanent information about peers * * This source is covered by the GNU GPL, the same as all kernel sources. * * 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/timer.h> #include <linux/time.h> #include <linux/kernel.h> #include <linux/mm.h> #include <linux/net.h> #include <linux/workqueue.h> #include <net/ip.h> #include <net/inetpeer.h> #include <net/secure_seq.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. * * 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 RB 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 lock held. * 2. Nodes may disappear from the tree only with the pool lock held * AND reference count being 0. * 3. Global variable peer_total is modified under the pool lock. * 4. struct inet_peer fields modification: * rb_node: pool lock * refcnt: atomically against modifications on other CPU; * usually under some other lock to prevent node disappearing * daddr: unchangeable */ static struct kmem_cache *peer_cachep __read_mostly; void inet_peer_base_init(struct inet_peer_base *bp) { bp->rb_root = RB_ROOT; seqlock_init(&bp->lock); bp->total = 0; } EXPORT_SYMBOL_GPL(inet_peer_base_init); #define PEER_MAX_GC 32 /* Exported for sysctl_net_ipv4. */ int inet_peer_threshold __read_mostly = 65536 + 128; /* start to throw entries more * aggressively at this stage */ int inet_peer_minttl __read_mostly = 120 * HZ; /* TTL under high load: 120 sec */ int inet_peer_maxttl __read_mostly = 10 * 60 * HZ; /* usual time to live: 10 min */ /* 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 | SLAB_PANIC, NULL); } /* Called with rcu_read_lock() or base->lock held */ static struct inet_peer *lookup(const struct inetpeer_addr *daddr, struct inet_peer_base *base, unsigned int seq, struct inet_peer *gc_stack[], unsigned int *gc_cnt, struct rb_node **parent_p, struct rb_node ***pp_p) { struct rb_node **pp, *parent, *next; struct inet_peer *p; pp = &base->rb_root.rb_node; parent = NULL; while (1) { int cmp; next = rcu_dereference_raw(*pp); if (!next) break; parent = next; p = rb_entry(parent, struct inet_peer, rb_node); cmp = inetpeer_addr_cmp(daddr, &p->daddr); if (cmp == 0) { if (!refcount_inc_not_zero(&p->refcnt)) break; return p; } if (gc_stack) { if (*gc_cnt < PEER_MAX_GC) gc_stack[(*gc_cnt)++] = p; } else if (unlikely(read_seqretry(&base->lock, seq))) { break; } if (cmp == -1) pp = &next->rb_left; else pp = &next->rb_right; } *parent_p = parent; *pp_p = pp; return NULL; }


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