/*
 * inet fragments management
 *
 *              This program is free software; you can redistribute it and/or
 *              modify it under the terms of the GNU General Public License
 *              as published by the Free Software Foundation; either version
 *              2 of the License, or (at your option) any later version.
 *
 *              Authors:        Pavel Emelyanov <xemul@openvz.org>
 *                              Started as consolidation of ipv4/ip_fragment.c,
 *                              ipv6/reassembly. and ipv6 nf conntrack reassembly
 */

#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/module.h>
#include <linux/timer.h>
#include <linux/mm.h>
#include <linux/random.h>
#include <linux/skbuff.h>
#include <linux/rtnetlink.h>

#include <net/inet_frag.h>

static void inet_frag_secret_rebuild(unsigned long dummy)
{
        struct inet_frags *f = (struct inet_frags *)dummy;
        unsigned long now = jiffies;
        int i;

        write_lock(&f->lock);
        get_random_bytes(&f->rnd, sizeof(u32));
        for (i = 0; i < INETFRAGS_HASHSZ; i++) {
                struct inet_frag_queue *q;
                struct hlist_node *p, *n;

                hlist_for_each_entry_safe(q, p, n, &f->hash[i], list) {
                        unsigned int hval = f->hashfn(q);

                        if (hval != i) {
                                hlist_del(&q->list);

                                /* Relink to new hash chain. */
                                hlist_add_head(&q->list, &f->hash[hval]);
                        }
                }
        }
        write_unlock(&f->lock);

        mod_timer(&f->secret_timer, now + f->secret_interval);
}

void inet_frags_init(struct inet_frags *f)
{
        int i;

        for (i = 0; i < INETFRAGS_HASHSZ; i++)
                INIT_HLIST_HEAD(&f->hash[i]);

        rwlock_init(&f->lock);

        f->rnd = (u32) ((num_physpages ^ (num_physpages>>7)) ^
                                   (jiffies ^ (jiffies >> 6)));

        setup_timer(&f->secret_timer, inet_frag_secret_rebuild,
                        (unsigned long)f);
        f->secret_timer.expires = jiffies + f->secret_interval;
        add_timer(&f->secret_timer);
}
EXPORT_SYMBOL(inet_frags_init);

void inet_frags_init_net(struct netns_frags *nf)
{
        nf->nqueues = 0;
        atomic_set(&nf->mem, 0);
        INIT_LIST_HEAD(&nf->lru_list);
}
EXPORT_SYMBOL(inet_frags_init_net);

void inet_frags_fini(struct inet_frags *f)
{
        del_timer(&f->secret_timer);
}
EXPORT_SYMBOL(inet_frags_fini);

void inet_frags_exit_net(struct netns_frags *nf, struct inet_frags *f)
{
        nf->low_thresh = 0;

        local_bh_disable();
        inet_frag_evictor(nf, f);
        local_bh_enable();
}
EXPORT_SYMBOL(inet_frags_exit_net);

static inline void fq_unlink(struct inet_frag_queue *fq, struct inet_frags *f)
{
        write_lock(&f->lock);
        hlist_del(&fq->list);
        list_del(&fq->lru_list);
        fq->net->nqueues--;
        write_unlock(&f->lock);
}

void inet_frag_kill(struct inet_frag_queue *fq, struct inet_frags *f)
{
        if (del_timer(&fq->timer))
                atomic_dec(&fq->refcnt);

        if (!(fq->last_in & INET_FRAG_COMPLETE)) {
                fq_unlink(fq, f);
                atomic_dec(&fq->refcnt);
                fq->last_in |= INET_FRAG_COMPLETE;
        }
}

EXPORT_SYMBOL(inet_frag_kill);

static inline void frag_kfree_skb(struct netns_frags *nf, struct inet_frags *f,
                struct sk_buff *skb, int *work)
{
        if (work)
                *work -= skb->truesize;

        atomic_sub(skb->truesize, &nf->mem);
        if (f->skb_free)
                f->skb_free(skb);
        kfree_skb(skb);
}

void inet_frag_destroy(struct inet_frag_queue *q, struct inet_frags *f,
                                        int *work)
{
        struct sk_buff *fp;
        struct netns_frags *nf;

        WARN_ON(!(q->last_in & INET_FRAG_COMPLETE));
        WARN_ON(del_timer(&q->timer) != 0);

        /* Release all fragment data. */
        fp = q->fragments;
        nf = q->net;
        while (fp) {
                struct sk_buff *xp = fp->next;

                frag_kfree_skb(nf, f, fp, work);
                fp = xp;
        }

        if (work)
                *work -= f->qsize;
        atomic_sub(f->qsize, &nf->mem);

        if (f->destructor)
                f->destructor(q);
        kfree(q);

}
EXPORT_SYMBOL(inet_frag_destroy);

int inet_frag_evictor(struct netns_frags *nf, struct inet_frags *f)
{
        struct inet_frag_queue *q;
        int work, evicted = 0;

        work = atomic_read(&nf->mem) - nf->low_thresh;
        while (work > 0) {
                read_lock(&f->lock);
                if (list_empty(&nf->lru_list)) {
                        read_unlock(&f->lock);
                        break;
                }

                q = list_first_entry(&nf->lru_list,
                                struct inet_frag_queue, lru_list);
                atomic_inc(&q->refcnt);
                read_unlock(&f->lock);

                spin_lock(&q->lock);
                if (!(q->last_in & INET_FRAG_COMPLETE))
                        inet_frag_kill(q, f);
                spin_unlock(&q->lock);

                if (atomic_dec_and_test(&q->refcnt))
                        inet_frag_destroy(q, f, &work);
                evicted++;
        }

        return evicted;
}
EXPORT_SYMBOL(inet_frag_evictor);

static struct inet_frag_queue *inet_frag_intern(struct netns_frags *nf,
                struct inet_frag_queue *qp_in, struct inet_frags *f,
                void *arg)
{
        struct inet_frag_queue *qp;
#ifdef CONFIG_SMP
        struct hlist_node *n;
#endif
        unsigned int hash;

        write_lock(&f->lock);
        /*
         * While we stayed w/o the lock other CPU could update
         * the rnd seed, so we need to re-calculate the hash
         * chain. Fortunatelly the qp_in can be used to get one.
         */
        hash = f->hashfn(qp_in);
#ifdef CONFIG_SMP
        /* With SMP race we have to recheck hash table, because
         * such entry could be created on other cpu, while we
         * promoted read lock to write lock.
         */
        hlist_for_each_entry(qp, n, &f->hash[hash], list) {
                if (qp->net == nf && f->match(qp, arg)) {
                        atomic_inc(&qp->refcnt);
                        write_unlock(&f->lock);
                        qp_in->last_in |= INET_FRAG_COMPLETE;
                        inet_frag_put(qp_in, f);
                        return qp;
                }
        }
#endif
        qp = qp_in;
        if (!mod_timer(&qp->timer, jiffies + nf->timeout))
                atomic_inc(&qp->refcnt);

        atomic_inc(&qp->refcnt);
        hlist_add_head(&qp->list, &f->hash[hash]);
        list_add_tail(&qp->lru_list, &nf->lru_list);
        nf->nqueues++;
        write_unlock(&f->lock);
        return qp;
}

static struct inet_frag_queue *inet_frag_alloc(struct netns_frags *nf,
                struct inet_frags *f, void *arg)
{
        struct inet_frag_queue *q;

        q = kzalloc(f->qsize, GFP_ATOMIC);
        if (q == NULL)
                return NULL;

        f->constructor(q, arg);
        atomic_add(f->qsize, &nf->mem);
        setup_timer(&q->timer, f->frag_expire, (unsigned long)q);
        spin_lock_init(&q->lock);
        atomic_set(&q->refcnt, 1);
        q->net = nf;

        return q;
}

static struct inet_frag_queue *inet_frag_create(struct netns_frags *nf,
                struct inet_frags *f, void *arg)
{
        struct inet_frag_queue *q;

        q = inet_frag_alloc(nf, f, arg);
        if (q == NULL)
                return NULL;

        return inet_frag_intern(nf, q, f, arg);
}

struct inet_frag_queue *inet_frag_find(struct netns_frags *nf,
                struct inet_frags *f, void *key, unsigned int hash)
        __releases(&f->lock)
{
        struct inet_frag_queue *q;
        struct hlist_node *n;

        hlist_for_each_entry(q, n, &f->hash[hash], list) {
                if (q->net == nf && f->match(q, key)) {
                        atomic_inc(&q->refcnt);
                        read_unlock(&f->lock);
                        return q;
                }
        }
        read_unlock(&f->lock);

        return inet_frag_create(nf, f, key);
}
EXPORT_SYMBOL(inet_frag_find);