/* flow.c: Generic flow cache.
 *
 * Copyright (C) 2003 Alexey N. Kuznetsov (kuznet@ms2.inr.ac.ru)
 * Copyright (C) 2003 David S. Miller (davem@redhat.com)
 */

#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 <linux/mutex.h>
#include <net/flow.h>
#include <linux/atomic.h>
#include <linux/security.h>
#include <net/net_namespace.h>

struct flow_cache_entry {
        union {
                struct hlist_node       hlist;
                struct list_head        gc_list;
        } u;
        struct net                      *net;
        u16                             family;
        u8                              dir;
        u32                             genid;
        struct flowi                    key;
        struct flow_cache_object        *object;
};

struct flow_flush_info {
        struct flow_cache               *cache;
        atomic_t                        cpuleft;
        struct completion               completion;
};

static struct kmem_cache *flow_cachep __read_mostly;

#define flow_cache_hash_size(cache)     (1 << (cache)->hash_shift)
#define FLOW_HASH_RND_PERIOD            (10 * 60 * HZ)

static void flow_cache_new_hashrnd(unsigned long arg)
{
        struct flow_cache *fc = (void *) arg;
        int i;

        for_each_possible_cpu(i)
                per_cpu_ptr(fc->percpu, i)->hash_rnd_recalc = 1;

        fc->rnd_timer.expires = jiffies + FLOW_HASH_RND_PERIOD;
        add_timer(&fc->rnd_timer);
}

static int flow_entry_valid(struct flow_cache_entry *fle,
                                struct net *net)
{
        if (atomic_read(&net->flow_cache_genid) != fle->genid)
                return 0;
        if (fle->object && !fle->object->ops->check(fle->object))
                return 0;
        return 1;
}

static void flow_entry_kill(struct flow_cache_entry *fle,
                                struct net *net)
{
        if (fle->object)
                fle->object->ops->delete(fle->object);
        kmem_cache_free(flow_cachep, fle);
}

static void flow_cache_gc_task(struct work_struct *work)
{
        struct list_head gc_list;
        struct flow_cache_entry *fce, *n;
        struct net *net = container_of(work, struct net, flow_cache_gc_work);

        INIT_LIST_HEAD(&gc_list);
        spin_lock_bh(&net->flow_cache_gc_lock);
        list_splice_tail_init(&net->flow_cache_gc_list, &gc_list);
        spin_unlock_bh(&net->flow_cache_gc_lock);

        list_for_each_entry_safe(fce, n, &gc_list, u.gc_list)
                flow_entry_kill(fce, net);
}

static void flow_cache_queue_garbage(struct flow_cache_percpu *fcp,
                                     int deleted, struct list_head *gc_list,
                                     struct net *net)
{
        if (deleted) {
                fcp->hash_count -= deleted;
                spin_lock_bh(&net->flow_cache_gc_lock);
                list_splice_tail(gc_list, &net->flow_cache_gc_list);
                spin_unlock_bh(&net->flow_cache_gc_lock);
                schedule_work(&net->flow_cache_gc_work);
        }
}

static void __flow_cache_shrink(struct flow_cache *fc,
                                struct flow_cache_percpu *fcp,
                                int shrink_to)
{
        struct flow_cache_entry *fle;
        struct hlist_node *tmp;
        LIST_HEAD(gc_list);
        int i, deleted = 0;
        struct net *net = container_of(fc, struct net, flow_cache_global);

        for (i = 0; i < flow_cache_hash_size(fc); i++) {
                int saved = 0;

                hlist_for_each_entry_safe(fle, tmp,
                                          &fcp->hash_table[i], u.hlist) {
                        if (saved < shrink_to &&
                            flow_entry_valid(fle, net)) {
                                saved++;
                        } else {
                                deleted++;
                                hlist_del(&fle->u.hlist);
                                list_add_tail(&fle->u.gc_list, &gc_list);
                        }
                }
        }

        flow_cache_queue_garbage(fcp, deleted, &gc_list, net);
}

static void flow_cache_shrink(struct flow_cache *fc,
                              struct flow_cache_percpu *fcp)
{
        int shrink_to = fc->low_watermark / flow_cache_hash_size(fc);

        __flow_cache_shrink(fc, fcp, shrink_to);
}

static void flow_new_hash_rnd(struct flow_cache *fc,
                              struct flow_cache_percpu *fcp)
{
        get_random_bytes(&fcp->hash_rnd, sizeof(u32));
        fcp->hash_rnd_recalc = 0;
        __flow_cache_shrink(fc, fcp, 0);
}

static u32 flow_hash_code(struct flow_cache *fc,
                          struct flow_cache_percpu *fcp,
                          const struct flowi *key,
                          size_t keysize)
{
        const u32 *k = (const u32 *) key;
        const u32 length = keysize * sizeof(flow_compare_t) / sizeof(u32);

        return jhash2(k, length, fcp->hash_rnd)
                & (flow_cache_hash_size(fc) - 1);
}

/* I hear what you're saying, use memcmp.  But memcmp cannot make
 * important assumptions that we can here, such as alignment.
 */
static int flow_key_compare(const struct flowi *key1, const struct flowi *key2,
                            size_t keysize)
{
        const flow_compare_t *k1, *k1_lim, *k2;

        k1 = (const flow_compare_t *) key1;
        k1_lim = k1 + keysize;

        k2 = (const flow_compare_t *) key2;

        do {
                if (*k1++ != *k2++)
                        return 1;
        } while (k1 < k1_lim);

        return 0;
}

struct flow_cache_object *
flow_cache_lookup(struct net *net, const struct flowi *key, u16 family, u8 dir,
                  flow_resolve_t resolver, void *ctx)
{
        struct flow_cache *fc = &net->flow_cache_global;
        struct flow_cache_percpu *fcp;
        struct flow_cache_entry *fle, *tfle;
        struct flow_cache_object *flo;
        size_t keysize;
        unsigned int hash;

        local_bh_disable();
        fcp = this_cpu_ptr(fc->percpu);

        fle = NULL;
        flo = NULL;

        keysize = flow_key_size(family);
        if (!keysize)
                goto nocache;

        /* Packet really early in init?  Making flow_cache_init a
         * pre-smp initcall would solve this.  --RR */
        if (!fcp->hash_table)
                goto nocache;

        if (fcp->hash_rnd_recalc)
                flow_new_hash_rnd(fc, fcp);

        hash = flow_hash_code(fc, fcp, key, keysize);
        hlist_for_each_entry(tfle, &fcp->hash_table[hash], u.hlist) {
                if (tfle->net == net &&
                    tfle->family == family &&
                    tfle->dir == dir &&
                    flow_key_compare(key, &tfle->key, keysize) == 0) {
                        fle = tfle;
                        break;
                }
        }

        if (unlikely(!fle)) {
                if (fcp->hash_count > fc->high_watermark)
                        flow_cache_shrink(fc, fcp);

                fle = kmem_cache_alloc(flow_cachep, GFP_ATOMIC);
                if (fle) {
                        fle->net = net;
                        fle->family = family;
                        fle->dir = dir;
                        memcpy(&fle->key, key, keysize * sizeof(flow_compare_t));
                        fle->object = NULL;
                        hlist_add_head(&fle->u.hlist, &fcp->hash_table[hash]);
                        fcp->hash_count++;
                }
        } else if (likely(fle->genid == atomic_read(&net->flow_cache_genid))) {
                flo = fle->object;
                if (!flo)
                        goto ret_object;
                flo = flo->ops->get(flo);
                if (flo)
                        goto ret_object;
        } else if (fle->object) {
                flo = fle->object;
                flo->ops->delete(flo);
                fle->object = NULL;
        }

nocache:
        flo = NULL;
        if (fle) {
                flo = fle->object;
                fle->object = NULL;
        }
        flo = resolver(net, key, family, dir, flo, ctx);
        if (fle) {
                fle->genid = atomic_read(&net->flow_cache_genid);
                if (!IS_ERR(flo))
                        fle->object = flo;
                else
                        fle->genid--;
        } else {
                if (!IS_ERR_OR_NULL(flo))
                        flo->ops->delete(flo);
        }
ret_object:
        local_bh_enable();
        return flo;
}
EXPORT_SYMBOL(flow_cache_lookup);

static void flow_cache_flush_tasklet(unsigned long data)
{
        struct flow_flush_info *info = (void *)data;
        struct flow_cache *fc = info->cache;
        struct flow_cache_percpu *fcp;
        struct flow_cache_entry *fle;
        struct hlist_node *tmp;
        LIST_HEAD(gc_list);
        int i, deleted = 0;
        struct net *net = container_of(fc, struct net, flow_cache_global);

        fcp = this_cpu_ptr(fc->percpu);
        for (i = 0; i < flow_cache_hash_size(fc); i++) {
                hlist_for_each_entry_safe(fle, tmp,
                                          &fcp->hash_table[i], u.hlist) {
                        if (flow_entry_valid(fle, net))
                                continue;

                        deleted++;
                        hlist_del(&fle->u.hlist);
                        list_add_tail(&fle->u.gc_list, &gc_list);
                }
        }

        flow_cache_queue_garbage(fcp, deleted, &gc_list, net);

        if (atomic_dec_and_test(&info->cpuleft))
                complete(&info->completion);
}

/*
 * Return whether a cpu needs flushing.  Conservatively, we assume
 * the presence of any entries means the core may require flushing,
 * since the flow_cache_ops.check() function may assume it's running
 * on the same core as the per-cpu cache component.
 */
static int flow_cache_percpu_empty(struct flow_cache *fc, int cpu)
{
        struct flow_cache_percpu *fcp;
        int i;

        fcp = per_cpu_ptr(fc->percpu, cpu);
        for (i = 0; i < flow_cache_hash_size(fc); i++)
                if (!hlist_empty(&fcp->hash_table[i]))
                        return 0;
        return 1;
}

static void flow_cache_flush_per_cpu(void *data)
{
        struct flow_flush_info *info = data;
        struct tasklet_struct *tasklet;

        tasklet = &this_cpu_ptr(info->cache->percpu)->flush_tasklet;
        tasklet->data = (unsigned long)info;
        tasklet_schedule(tasklet);
}

void flow_cache_flush(struct net *net)
{
        struct flow_flush_info info;
        cpumask_var_t mask;
        int i, self;

        /* Track which cpus need flushing to avoid disturbing all cores. */
        if (!alloc_cpumask_var(&mask, GFP_KERNEL))
                return;
        cpumask_clear(mask);

        /* Don't want cpus going down or up during this. */
        get_online_cpus();
        mutex_lock(&net->flow_flush_sem);
        info.cache = &net->flow_cache_global;
        for_each_online_cpu(i)
                if (!flow_cache_percpu_empty(info.cache, i))
                        cpumask_set_cpu(i, mask);
        atomic_set(&info.cpuleft, cpumask_weight(mask));
        if (atomic_read(&info.cpuleft) == 0)
                goto done;

        init_completion(&info.completion);

        local_bh_disable();
        self = cpumask_test_and_clear_cpu(smp_processor_id(), mask);
        on_each_cpu_mask(mask, flow_cache_flush_per_cpu, &info, 0);
        if (self)
                flow_cache_flush_tasklet((unsigned long)&info);
        local_bh_enable();

        wait_for_completion(&info.completion);

done:
        mutex_unlock(&net->flow_flush_sem);
        put_online_cpus();
        free_cpumask_var(mask);
}

static void flow_cache_flush_task(struct work_struct *work)
{
        struct net *net = container_of(work, struct net, flow_cache_flush_work);

        flow_cache_flush(net);
}

void flow_cache_flush_deferred(struct net *net)
{
        schedule_work(&net->flow_cache_flush_work);
}

static int flow_cache_cpu_prepare(struct flow_cache *fc, int cpu)
{
        struct flow_cache_percpu *fcp = per_cpu_ptr(fc->percpu, cpu);
        size_t sz = sizeof(struct hlist_head) * flow_cache_hash_size(fc);

        if (!fcp->hash_table) {
                fcp->hash_table = kzalloc_node(sz, GFP_KERNEL, cpu_to_node(cpu));
                if (!fcp->hash_table) {
                        pr_err("NET: failed to allocate flow cache sz %zu\n", sz);
                        return -ENOMEM;
                }
                fcp->hash_rnd_recalc = 1;
                fcp->hash_count = 0;
                tasklet_init(&fcp->flush_tasklet, flow_cache_flush_tasklet, 0);
        }
        return 0;
}

static int flow_cache_cpu(struct notifier_block *nfb,
                          unsigned long action,
                          void *hcpu)
{
        struct flow_cache *fc = container_of(nfb, struct flow_cache,
                                                hotcpu_notifier);
        int res, cpu = (unsigned long) hcpu;
        struct flow_cache_percpu *fcp = per_cpu_ptr(fc->percpu, cpu);

        switch (action) {
        case CPU_UP_PREPARE:
        case CPU_UP_PREPARE_FROZEN:
                res = flow_cache_cpu_prepare(fc, cpu);
                if (res)
                        return notifier_from_errno(res);
                break;
        case CPU_DEAD:
        case CPU_DEAD_FROZEN:
                __flow_cache_shrink(fc, fcp, 0);
                break;
        }
        return NOTIFY_OK;
}

int flow_cache_init(struct net *net)
{
        int i;
        struct flow_cache *fc = &net->flow_cache_global;

        if (!flow_cachep)
                flow_cachep = kmem_cache_create("flow_cache",
                                                sizeof(struct flow_cache_entry),
                                                0, SLAB_PANIC, NULL);
        spin_lock_init(&net->flow_cache_gc_lock);
        INIT_LIST_HEAD(&net->flow_cache_gc_list);
        INIT_WORK(&net->flow_cache_gc_work, flow_cache_gc_task);
        INIT_WORK(&net->flow_cache_flush_work, flow_cache_flush_task);
        mutex_init(&net->flow_flush_sem);

        fc->hash_shift = 10;
        fc->low_watermark = 2 * flow_cache_hash_size(fc);
        fc->high_watermark = 4 * flow_cache_hash_size(fc);

        fc->percpu = alloc_percpu(struct flow_cache_percpu);
        if (!fc->percpu)
                return -ENOMEM;

        cpu_notifier_register_begin();

        for_each_online_cpu(i) {
                if (flow_cache_cpu_prepare(fc, i))
                        goto err;
        }
        fc->hotcpu_notifier = (struct notifier_block){
                .notifier_call = flow_cache_cpu,
        };
        __register_hotcpu_notifier(&fc->hotcpu_notifier);

        cpu_notifier_register_done();

        setup_timer(&fc->rnd_timer, flow_cache_new_hashrnd,
                    (unsigned long) fc);
        fc->rnd_timer.expires = jiffies + FLOW_HASH_RND_PERIOD;
        add_timer(&fc->rnd_timer);

        return 0;

err:
        for_each_possible_cpu(i) {
                struct flow_cache_percpu *fcp = per_cpu_ptr(fc->percpu, i);
                kfree(fcp->hash_table);
                fcp->hash_table = NULL;
        }

        cpu_notifier_register_done();

        free_percpu(fc->percpu);
        fc->percpu = NULL;

        return -ENOMEM;
}
EXPORT_SYMBOL(flow_cache_init);

void flow_cache_fini(struct net *net)
{
        int i;
        struct flow_cache *fc = &net->flow_cache_global;

        del_timer_sync(&fc->rnd_timer);
        unregister_hotcpu_notifier(&fc->hotcpu_notifier);

        for_each_possible_cpu(i) {
                struct flow_cache_percpu *fcp = per_cpu_ptr(fc->percpu, i);
                kfree(fcp->hash_table);
                fcp->hash_table = NULL;
        }

        free_percpu(fc->percpu);
        fc->percpu = NULL;
}
EXPORT_SYMBOL(flow_cache_fini);