* Copyright (C) 2003 David S. Miller ([EMAIL="davem@redhat.com"]davem@redhat.com[/EMAIL])
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/list.h>
#include <linux/jhash.h>
#include <linux/interrupt.h>
#include <linux/mm.h>
#include <linux/random.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/smp.h>
#include <linux/completion.h>
#include <linux/percpu.h>
#include <linux/bitops.h>
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <linux/cpumask.h>
#include <net/flow.h>
#include <asm/atomic.h>
#include <asm/semaphore.h>
struct flow_cache_entry {
struct flow_cache_entry *next;
u16 family;
u8 dir;
struct flowi key;
u32 genid;
void *object;
atomic_t *object_ref;
};
atomic_t flow_cache_genid = ATOMIC_INIT(0);
static u32 flow_hash_shift;
#define flow_hash_size (1 << flow_hash_shift)
static DEFINE_PER_CPU(struct flow_cache_entry **, flow_tables) = { NULL };
#define flow_table(cpu) (per_cpu(flow_tables, cpu))
static kmem_cache_t *flow_cachep;
static int flow_lwm, flow_hwm;
struct flow_percpu_info {
int hash_rnd_recalc;
u32 hash_rnd;
int count;
} ____cacheline_aligned;
static DEFINE_PER_CPU(struct flow_percpu_info, flow_hash_info) = { 0 };
#define flow_hash_rnd_recalc(cpu) \
(per_cpu(flow_hash_info, cpu).hash_rnd_recalc)
#define flow_hash_rnd(cpu) \
(per_cpu(flow_hash_info, cpu).hash_rnd)
#define flow_count(cpu) \
(per_cpu(flow_hash_info, cpu).count)
static struct timer_list flow_hash_rnd_timer;
#define FLOW_HASH_RND_PERIOD (10 * 60 * HZ)
struct flow_flush_info {
atomic_t cpuleft;
struct completion completion;
};
static DEFINE_PER_CPU(struct tasklet_struct, flow_flush_tasklets) = { NULL };
#define flow_flush_tasklet(cpu) (&per_cpu(flow_flush_tasklets, cpu))
static void flow_cache_new_hashrnd(unsigned long arg)
{
int i;
for_each_cpu(i)
flow_hash_rnd_recalc(i) = 1;
flow_hash_rnd_timer.expires = jiffies + FLOW_HASH_RND_PERIOD;
add_timer(&flow_hash_rnd_timer);
}
static void __flow_cache_shrink(int cpu, int shrink_to)
{
struct flow_cache_entry *fle, **flp;
int i;
for (i = 0; i < flow_hash_size; i++) {
int k = 0;
flp = &flow_table(cpu)
;
while ((fle = *flp) != NULL && k < shrink_to) {
k++;
flp = &fle->next;
}
while ((fle = *flp) != NULL) {
*flp = fle->next;
if (fle->object)
atomic_dec(fle->object_ref);
kmem_cache_free(flow_cachep, fle);
flow_count(cpu)--;
}
}
}
static void flow_cache_shrink(int cpu)
{
int shrink_to = flow_lwm / flow_hash_size;
__flow_cache_shrink(cpu, shrink_to);
}
static void flow_new_hash_rnd(int cpu)
{
get_random_bytes(&flow_hash_rnd(cpu), sizeof(u32));
flow_hash_rnd_recalc(cpu) = 0;
__flow_cache_shrink(cpu, 0);
}
static u32 flow_hash_code(struct flowi *key, int cpu)
{
u32 *k = (u32 *) key;
return (jhash2(k, (sizeof(*key) / sizeof(u32)), flow_hash_rnd(cpu)) &
(flow_hash_size - 1));
}
#if (BITS_PER_LONG == 64)
typedef u64 flow_compare_t;
#else
typedef u32 flow_compare_t;
#endif
extern void flowi_is_missized(void);
/* I hear what you're saying, use memcmp. But memcmp cannot make
* important assumptions that we can here, such as alignment and
* constant size.
*/
static int flow_key_compare(struct flowi *key1, struct flowi *key2)
{
flow_compare_t *k1, *k1_lim, *k2;
const int n_elem = sizeof(struct flowi) / sizeof(flow_compare_t);
if (sizeof(struct flowi) % sizeof(flow_compare_t))
flowi_is_missized();
k1 = (flow_compare_t *) key1;
k1_lim = k1 + n_elem;
k2 = (flow_compare_t *) key2;
do {
if (*k1++ != *k2++)
return 1;
} while (k1 < k1_lim);
return 0;
}
void *flow_cache_lookup(struct flowi *key, u16 family, u8 dir,
flow_resolve_t resolver)
{
struct flow_cache_entry *fle, **head;
unsigned int hash;
int cpu;
local_bh_disable();
cpu = smp_processor_id();
fle = NULL;
/* Packet really early in init? Making flow_cache_init a
* pre-smp initcall would solve this. --RR */
if (!flow_table(cpu))
goto nocache;
if (flow_hash_rnd_recalc(cpu))
flow_new_hash_rnd(cpu);
hash = flow_hash_code(key, cpu);
head = &flow_table(cpu)[hash];
for (fle = *head; fle; fle = fle->next) {
if (fle->family == family &&
fle->dir == dir &&
flow_key_compare(key, &fle->key) == 0) {
if (fle->genid == atomic_read(&flow_cache_genid)) {
void *ret = fle->object;
if (ret)
atomic_inc(fle->object_ref);
local_bh_enable();
return ret;
}
break;
}
}
if (!fle) {
if (flow_count(cpu) > flow_hwm)
flow_cache_shrink(cpu);
fle = kmem_cache_alloc(flow_cachep, SLAB_ATOMIC);
if (fle) {
fle->next = *head;
*head = fle;
fle->family = family;
fle->dir = dir;
memcpy(&fle->key, key, sizeof(*key));
fle->object = NULL;
flow_count(cpu)++;
}
}
nocache:
{
void *obj;
atomic_t *obj_ref;
resolver(key, family, dir, &obj, &obj_ref);
if (fle) {
fle->genid = atomic_read(&flow_cache_genid);
if (fle->object)
atomic_dec(fle->object_ref);
fle->object = obj;
fle->object_ref = obj_ref;
if (obj)
atomic_inc(fle->object_ref);
}
local_bh_enable();
return obj;
}
}
static void flow_cache_flush_tasklet(unsigned long data)
{
struct flow_flush_info *info = (void *)data;
int i;
int cpu;
cpu = smp_processor_id();
for (i = 0; i < flow_hash_size; i++) {
struct flow_cache_entry *fle;
fle = flow_table(cpu);
for (; fle; fle = fle->next) {
unsigned genid = atomic_read(&flow_cache_genid);
if (!fle->object || fle->genid == genid)
continue;
fle->object = NULL;
atomic_dec(fle->object_ref);
}
}
if (atomic_dec_and_test(&info->cpuleft))
complete(&info->completion);
}
static void flow_cache_flush_per_cpu(void *) __attribute__((__unused__));
static void flow_cache_flush_per_cpu(void *data)
{
struct flow_flush_info *info = data;
int cpu;
struct tasklet_struct *tasklet;
cpu = smp_processor_id();
tasklet = flow_flush_tasklet(cpu);
tasklet->data = (unsigned long)info;
tasklet_schedule(tasklet);
}
void flow_cache_flush(void)
{
struct flow_flush_info info;
static DECLARE_MUTEX(flow_flush_sem);
/* Don't want cpus going down or up during this. */
lock_cpu_hotplug();
down(&flow_flush_sem);
atomic_set(&info.cpuleft, num_online_cpus());
init_completion(&info.completion);
local_bh_disable();
smp_call_function(flow_cache_flush_per_cpu, &info, 1, 0);
flow_cache_flush_tasklet((unsigned long)&info);
local_bh_enable();
wait_for_completion(&info.completion);
up(&flow_flush_sem);
unlock_cpu_hotplug();
}
static void __devinit flow_cache_cpu_prepare(int cpu)
{
struct tasklet_struct *tasklet;
unsigned long order;
for (order = 0;
(PAGE_SIZE << order) <
(sizeof(struct flow_cache_entry *)*flow_hash_size);
order++)
/* NOTHING */;
flow_table(cpu) = (struct flow_cache_entry **)
__get_free_pages(GFP_KERNEL, order);
if (!flow_table(cpu))
panic("NET: failed to allocate flow cache order %lu\n", order);
memset(flow_table(cpu), 0, PAGE_SIZE << order);
flow_hash_rnd_recalc(cpu) = 1;
flow_count(cpu) = 0;
tasklet = flow_flush_tasklet(cpu);
tasklet_init(tasklet, flow_cache_flush_tasklet, 0);
}
#ifdef CONFIG_HOTPLUG_CPU
static int flow_cache_cpu(struct notifier_block *nfb,
unsigned long action,
void *hcpu)
{
if (action == CPU_DEAD)
__flow_cache_shrink((unsigned long)hcpu, 0);
return NOTIFY_OK;
}
#endif /* CONFIG_HOTPLUG_CPU */
static int __init flow_cache_init(void)
{
int i;
flow_cachep = kmem_cache_create("flow_cache",
sizeof(struct flow_cache_entry),
0, SLAB_HWCACHE_ALIGN,
NULL, NULL);
if (!flow_cachep)
panic("NET: failed to allocate flow cache slab\n");
flow_hash_shift = 10;
flow_lwm = 2 * flow_hash_size;
flow_hwm = 4 * flow_hash_size;
init_timer(&flow_hash_rnd_timer);
flow_hash_rnd_timer.function = flow_cache_new_hashrnd;
flow_hash_rnd_timer.expires = jiffies + FLOW_HASH_RND_PERIOD;
add_timer(&flow_hash_rnd_timer);
for_each_cpu(i)
flow_cache_cpu_prepare(i);
hotcpu_notifier(flow_cache_cpu, 0);
return 0;
}
module_init(flow_cache_init);
EXPORT_SYMBOL(flow_cache_genid);
EXPORT_SYMBOL(flow_cache_lookup);
上面是代码 不怎么看的懂 希望有人给个注释 并帮忙指出控制流程和关键算法什么的 
