dst.c

Go to the documentation of this file.

/*
 * net/dst.c    Protocol independent destination cache.
 *
 * Authors:     Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
 *
 */

#include <linux/bitops.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/string.h>
#include <linux/errno.h>
#include <linux/netdevice.h>
#include <linux/skbuff.h>
#include <linux/init.h>

#include <net/dst.h>

/* Locking strategy:
 * 1) Garbage collection state of dead destination cache
 *    entries is protected by dst_lock.
 * 2) GC is run only from BH context, and is the only remover
 *    of entries.
 * 3) Entries are added to the garbage list from both BH
 *    and non-BH context, so local BH disabling is needed.
 * 4) All operations modify state, so a spinlock is used.
 */
static struct dst_entry         *dst_garbage_list;
#if RT_CACHE_DEBUG >= 2 
static atomic_t                  dst_total = ATOMIC_INIT(0);
#endif
static spinlock_t                dst_lock = SPIN_LOCK_UNLOCKED;

static unsigned long dst_gc_timer_expires;
static unsigned long dst_gc_timer_inc = DST_GC_MAX;
static void dst_run_gc(unsigned long);

static struct timer_list dst_gc_timer =
        { data: DST_GC_MIN, function: dst_run_gc };


static void dst_run_gc(unsigned long dummy)
{
        int    delayed = 0;
        struct dst_entry * dst, **dstp;

        if (!spin_trylock(&dst_lock)) {
                mod_timer(&dst_gc_timer, jiffies + HZ/10);
                return;
        }


        del_timer(&dst_gc_timer);
        dstp = &dst_garbage_list;
        while ((dst = *dstp) != NULL) {
                if (atomic_read(&dst->__refcnt)) {
                        dstp = &dst->next;
                        delayed++;
                        continue;
                }
                *dstp = dst->next;
                dst_destroy(dst);
        }
        if (!dst_garbage_list) {
                dst_gc_timer_inc = DST_GC_MAX;
                goto out;
        }
        if ((dst_gc_timer_expires += dst_gc_timer_inc) > DST_GC_MAX)
                dst_gc_timer_expires = DST_GC_MAX;
        dst_gc_timer_inc += DST_GC_INC;
        dst_gc_timer.expires = jiffies + dst_gc_timer_expires;
#if RT_CACHE_DEBUG >= 2
        printk("dst_total: %d/%d %ld\n",
               atomic_read(&dst_total), delayed,  dst_gc_timer_expires);
#endif
        add_timer(&dst_gc_timer);

out:
        spin_unlock(&dst_lock);
}

static int dst_discard(struct sk_buff *skb)
{
        kfree_skb(skb);
        return 0;
}

static int dst_blackhole(struct sk_buff *skb)
{
        kfree_skb(skb);
        return 0;
}

void * dst_alloc(struct dst_ops * ops)
{
        struct dst_entry * dst;

        if (ops->gc && atomic_read(&ops->entries) > ops->gc_thresh) {
                if (ops->gc())
                        return NULL;
        }
        dst = kmem_cache_alloc(ops->kmem_cachep, SLAB_ATOMIC);
        if (!dst)
                return NULL;
        memset(dst, 0, ops->entry_size);
        atomic_set(&dst->__refcnt, 0);
        dst->ops = ops;
        dst->lastuse = jiffies;
        dst->input = dst_discard;
        dst->output = dst_blackhole;
#if RT_CACHE_DEBUG >= 2 
        atomic_inc(&dst_total);
#endif
        atomic_inc(&ops->entries);
        return dst;
}

void __dst_free(struct dst_entry * dst)
{
        spin_lock_bh(&dst_lock);

        /* The first case (dev==NULL) is required, when
           protocol module is unloaded.
         */
        if (dst->dev == NULL || !(dst->dev->flags&IFF_UP)) {
                dst->input = dst_discard;
                dst->output = dst_blackhole;
        }
        dst->obsolete = 2;
        dst->next = dst_garbage_list;
        dst_garbage_list = dst;
        if (dst_gc_timer_inc > DST_GC_INC) {
                dst_gc_timer_inc = DST_GC_INC;
                dst_gc_timer_expires = DST_GC_MIN;
                mod_timer(&dst_gc_timer, jiffies + dst_gc_timer_expires);
        }

        spin_unlock_bh(&dst_lock);
}

void dst_destroy(struct dst_entry * dst)
{
        struct neighbour *neigh = dst->neighbour;
        struct hh_cache *hh = dst->hh;

        dst->hh = NULL;
        if (hh && atomic_dec_and_test(&hh->hh_refcnt))
                kfree(hh);

        if (neigh) {
                dst->neighbour = NULL;
                neigh_release(neigh);
        }

        atomic_dec(&dst->ops->entries);

        if (dst->ops->destroy)
                dst->ops->destroy(dst);
        if (dst->dev)
                dev_put(dst->dev);
#if RT_CACHE_DEBUG >= 2 
        atomic_dec(&dst_total);
#endif
        kmem_cache_free(dst->ops->kmem_cachep, dst);
}

static int dst_dev_event(struct notifier_block *this, unsigned long event, void *ptr)
{
        struct net_device *dev = ptr;
        struct dst_entry *dst;

        switch (event) {
        case NETDEV_UNREGISTER:
        case NETDEV_DOWN:
                spin_lock_bh(&dst_lock);
                for (dst = dst_garbage_list; dst; dst = dst->next) {
                        if (dst->dev == dev) {
                                /* Dirty hack. We did it in 2.2 (in __dst_free),
                                   we have _very_ good reasons not to repeat
                                   this mistake in 2.3, but we have no choice
                                   now. _It_ _is_ _explicit_ _deliberate_
                                   _race_ _condition_.
                                 */
                                if (event!=NETDEV_DOWN &&
                                    !(dev->features & NETIF_F_DYNALLOC) &&
                                    dst->output == dst_blackhole) {
                                        dst->dev = &loopback_dev;
                                        dev_put(dev);
                                        dev_hold(&loopback_dev);
                                        dst->output = dst_discard;
                                        if (dst->neighbour && dst->neighbour->dev == dev) {
                                                dst->neighbour->dev = &loopback_dev;
                                                dev_put(dev);
                                                dev_hold(&loopback_dev);
                                        }
                                } else {
                                        dst->input = dst_discard;
                                        dst->output = dst_blackhole;
                                }
                        }
                }
                spin_unlock_bh(&dst_lock);
                break;
        }
        return NOTIFY_DONE;
}

struct notifier_block dst_dev_notifier = {
        dst_dev_event,
        NULL,
        0
};

void __init dst_init(void)
{
        register_netdevice_notifier(&dst_dev_notifier);
}

---