A netgraph node implementing Netflow version 5.

Supported by:	Bestcom ISP, Rinet ISP
Approved by:	julian (mentor)

1 files changed, 736 insertions, 0 deletions

diff --git a/sys/netgraph/netflow/netflow.c b/sys/netgraph/netflow/netflow.c
new file mode 100644
index 0000000..1075838
--- /dev/null
+++ b/sys/netgraph/netflow/netflow.c
@@ -0,0 +1,736 @@
+/*-
+ * Copyright (c) 2004 Gleb Smirnoff <glebius@cell.sick.ru>
+ * Copyright (c) 2001-2003 Roman V. Palagin <romanp@unshadow.net>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. All advertising materials mentioning features or use of this software
+ *    must display the following acknowledgement:
+ * This product includes software developed by Gleb Smirnoff and
+ * contributors.
+ * 4. Neither the name of the author nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $SourceForge: netflow.c,v 1.41 2004/09/05 11:41:10 glebius Exp $
+ */
+
+static const char rcs_id[] =
+    "@(#) $FreeBSD$";
+
+#include <sys/param.h>
+#include <sys/kernel.h>
+#include <sys/limits.h>
+#include <sys/mbuf.h>
+#include <sys/systm.h>
+#include <sys/socket.h>
+
+#include <net/if.h>
+#include <net/if_var.h>
+#include <net/if_dl.h>
+#include <net/route.h>
+#include <netinet/in.h>
+#include <netinet/in_systm.h>
+#include <netinet/ip.h>
+#include <netinet/tcp.h>
+#include <netinet/udp.h>
+
+#include <netgraph/ng_message.h>
+#include <netgraph/netgraph.h>
+
+#include <netgraph/netflow/netflow.h>
+#include <netgraph/netflow/ng_netflow.h>
+
+#define	NBUCKETS	(4096)	/* must be power of 2 */
+
+/* This hash is for TCP or UDP packets */
+#define FULL_HASH(addr1,addr2,port1,port2)\
+	(((addr1 >> 16) ^		\
+	  (addr2 & 0x00FF) ^		\
+	  ((port1 ^ port2) << 8) )&	\
+	 (NBUCKETS - 1))
+
+/* This hash for all other IP packets */
+#define ADDR_HASH(addr1,addr2)\
+	(((addr1 >> 16) ^		\
+	  (addr2 & 0x00FF) )&		\
+	 (NBUCKETS - 1))
+
+/* Macros to shorten logical constructions */
+/* XXX: priv must exist in namespace */
+#define	INACTIVE(fle)	(time_uptime - fle->f.last > priv->info.nfinfo_inact_t)
+#define	AGED(fle)	(time_uptime - fle->f.first > priv->info.nfinfo_act_t)
+#define	ISFREE(fle)	(fle->f.packets == 0)
+
+/*
+ * 4 is a magical number: statistically number of 4-packet flows is
+ * bigger than 5,6,7...-packet flows by an order of magnitude. Most UDP/ICMP
+ * scans are 1 packet (~ 90% of flow cache). TCP scans are 2-packet in case
+ * of reachable host and 4-packet otherwise.
+ */
+#define	SMALL(fle)	(fle->f.packets <= 4)
+	
+MALLOC_DECLARE(M_NETFLOW);
+MALLOC_DEFINE(M_NETFLOW, "NetFlow", "flow cache");
+
+static int export_add(priv_p , struct flow_entry *);
+static int export_send(priv_p );
+
+/* Generate hash for a given flow record */
+static __inline uint32_t
+ip_hash(struct flow_rec *r)
+{
+	switch (r->r_ip_p) {
+	case IPPROTO_TCP:
+	case IPPROTO_UDP:
+		return FULL_HASH(r->r_src.s_addr, r->r_dst.s_addr,
+		    r->r_sport, r->r_dport);
+	default:
+		return ADDR_HASH(r->r_src.s_addr, r->r_dst.s_addr);
+	}
+}
+
+/* Lookup for record in given slot */
+static __inline struct flow_entry *
+hash_lookup(struct flow_hash_entry *h, int slot, struct flow_rec *r)
+{
+	struct flow_entry *fle;
+
+	LIST_FOREACH(fle, &(h[slot].head), fle_hash)
+		if (bcmp(r, &fle->f.r, sizeof(struct flow_rec)) == 0)
+			return (fle);
+
+	return (NULL);
+}
+
+/* Get a flow entry from free list */
+static __inline struct flow_entry *
+alloc_flow(priv_p priv, int *flows)
+{
+	register struct flow_entry	*fle;
+
+	mtx_lock(&priv->free_mtx);
+
+	if (SLIST_EMPTY(&priv->free_list)) {
+		mtx_unlock(&priv->free_mtx);
+		return(NULL);
+	}
+
+	fle = SLIST_FIRST(&priv->free_list);
+	SLIST_REMOVE_HEAD(&priv->free_list, fle_free);
+
+	priv->info.nfinfo_used++;
+	priv->info.nfinfo_free--;
+
+	if (flows != NULL)
+		*flows = priv->info.nfinfo_used;
+
+	mtx_unlock(&priv->free_mtx);
+
+	return (fle);
+}
+
+/* Insert flow entry into a free list. */
+static __inline int
+free_flow(priv_p priv, struct flow_entry *fle)
+{
+	int flows;
+
+	mtx_lock(&priv->free_mtx);
+	fle->f.packets = 0;
+	SLIST_INSERT_HEAD(&priv->free_list, fle, fle_free);
+	flows = priv->info.nfinfo_used--;
+	priv->info.nfinfo_free++;
+	mtx_unlock(&priv->free_mtx);
+
+	return flows;
+}
+
+#define	NGNF_GETUSED(priv, rval)	do {	\
+	mtx_lock(&priv->free_mtx);		\
+	rval = priv->info.nfinfo_used;		\
+	mtx_unlock(&priv->free_mtx);		\
+	} while (0)
+
+/* Insert flow entry into expire list. */
+/* XXX: Flow must be detached from work queue, but not from cache */
+static __inline void
+expire_flow(priv_p priv, struct flow_entry *fle)
+{
+	mtx_assert(&priv->work_mtx, MA_OWNED);
+	LIST_REMOVE(fle, fle_hash);
+
+	mtx_lock(&priv->expire_mtx);
+	SLIST_INSERT_HEAD(&priv->expire_list, fle, fle_free);
+	mtx_unlock(&priv->expire_mtx);
+}
+
+/* Get a snapshot of node statistics */
+void
+ng_netflow_copyinfo(priv_p priv, struct ng_netflow_info *i)
+{
+	mtx_lock(&priv->free_mtx);
+	memcpy((void *)i, (void *)&priv->info, sizeof(priv->info));
+	mtx_unlock(&priv->free_mtx);
+}
+
+/* Calculate number of bits in netmask */
+#define	g21	0x55555555ul	/* = 0101_0101_0101_0101_0101_0101_0101_0101 */
+#define	g22	0x33333333ul	/* = 0011_0011_0011_0011_0011_0011_0011_0011 */
+#define	g23	0x0f0f0f0ful	/* = 0000_1111_0000_1111_0000_1111_0000_1111 */
+static __inline u_char
+bit_count(uint32_t v)
+{
+	v = (v & g21) + ((v >> 1) & g21);
+	v = (v & g22) + ((v >> 2) & g22);
+	v = (v + (v >> 4)) & g23;
+	return (v + (v >> 8) + (v >> 16) + (v >> 24)) & 0x3f;
+}
+
+/*
+ * Insert a record into defined slot.
+ *
+ * First we get for us a free flow entry, then fill in all
+ * possible fields in it. Then obtain lock on flow cache
+ * and insert flow entry.
+ */
+static __inline int
+hash_insert(priv_p priv, int slot, struct flow_rec *r, int plen)
+{
+	struct flow_hash_entry	*h = priv->hash;
+	struct flow_entry	*fle;
+	struct route ro;
+	struct sockaddr_in *sin;
+
+	fle = alloc_flow(priv, NULL);
+	if (fle == NULL)
+		return (ENOMEM);
+
+	/*
+	 * Now fle is totally ours. It is detached from all lists,
+	 * we can safely edit it.
+	 */
+
+	bcopy(r, &fle->f.r, sizeof(struct flow_rec));
+	fle->f.bytes = plen;
+	fle->f.packets = 1;
+
+	priv->info.nfinfo_bytes += plen;
+
+	fle->f.first = fle->f.last = time_uptime;
+
+	/*
+	 * First we do route table lookup on destination address. So we can
+	 * fill in out_ifx, dst_mask, nexthop, and dst_as in future releases.
+	 */
+	bzero((caddr_t)&ro, sizeof(ro));
+	sin = (struct sockaddr_in *)&ro.ro_dst;
+	sin->sin_len = sizeof(*sin);
+	sin->sin_family = AF_INET;
+	sin->sin_addr = fle->f.r.r_dst;
+	rtalloc_ign(&ro, RTF_CLONING);
+	if (ro.ro_rt != NULL) {
+		struct rtentry *rt = ro.ro_rt;
+
+		fle->f.fle_o_ifx = rt->rt_ifp->if_index;
+
+		if (rt->rt_flags & RTF_GATEWAY &&
+		    rt->rt_gateway->sa_family == AF_INET)
+			fle->f.next_hop =
+			    ((struct sockaddr_in *)(rt->rt_gateway))->sin_addr;
+
+		if (rt_mask(rt))
+			fle->f.dst_mask =
+			    bit_count(((struct sockaddr_in *)rt_mask(rt))->sin_addr.s_addr);
+		else if (rt->rt_flags & RTF_HOST)
+			/* Give up. We can't determine mask :( */
+			fle->f.dst_mask = 32;
+
+		RTFREE(ro.ro_rt);
+	}
+
+	/* Do route lookup on source address, to fill in src_mask. */
+
+	bzero((caddr_t)&ro, sizeof(ro));
+	sin = (struct sockaddr_in *)&ro.ro_dst;
+	sin->sin_len = sizeof(*sin);
+	sin->sin_family = AF_INET;
+	sin->sin_addr = fle->f.r.r_src;
+	rtalloc_ign(&ro, RTF_CLONING);
+	if (ro.ro_rt != NULL) {
+		struct rtentry *rt = ro.ro_rt;
+
+		if (rt_mask(rt))
+			fle->f.src_mask =
+			    bit_count(((struct sockaddr_in *)rt_mask(rt))->sin_addr.s_addr);
+		else if (rt->rt_flags & RTF_HOST)
+			/* Give up. We can't determine mask :( */
+			fle->f.src_mask = 32;
+
+		RTFREE(ro.ro_rt);
+	}
+
+	/* Push new flow entry into flow cache */
+	mtx_lock(&priv->work_mtx);
+	LIST_INSERT_HEAD(&(h[slot].head), fle, fle_hash);
+	TAILQ_INSERT_TAIL(&priv->work_queue, fle, fle_work);
+	mtx_unlock(&priv->work_mtx);
+
+	return (0);
+}
+
+static __inline int
+make_flow_rec(struct mbuf **m, int *plen, struct flow_rec *r, uint8_t *tcp_flags,
+	u_int16_t i_ifx)
+{
+	register struct ip *ip;
+	int hlen;
+	int error = 0;
+
+	ip = mtod(*m, struct ip*);
+
+	/* check version */
+	if (ip->ip_v != IPVERSION)
+		return (EINVAL);
+
+	/* verify min header length */
+	hlen = ip->ip_hl << 2;
+
+	if (hlen < sizeof(struct ip))
+		return (EINVAL);
+
+	r->r_src = ip->ip_src;
+	r->r_dst = ip->ip_dst;
+
+	/* save packet length */
+	*plen = ntohs(ip->ip_len);
+
+	r->r_ip_p = ip->ip_p;
+	r->r_tos = ip->ip_tos;
+
+	if ((*m)->m_pkthdr.rcvif)
+		r->r_i_ifx = (*m)->m_pkthdr.rcvif->if_index;
+	else
+		r->r_i_ifx = i_ifx;
+
+	/*
+	 * XXX NOTE: only first fragment of fragmented TCP, UDP and
+	 * ICMP packet will be recorded with proper s_port and d_port.
+	 * Following fragments will be recorded simply as IP packet with
+	 * ip_proto = ip->ip_p and s_port, d_port set to zero.
+	 * I know, it looks like bug. But I don't want to re-implement
+	 * ip packet assebmling here. Anyway, (in)famous trafd works this way -
+	 * and nobody complains yet :)
+	 */
+	if(ip->ip_off & htons(IP_OFFMASK))
+		return (0);
+
+	/* skip IP header */
+	m_adj(*m, hlen);
+
+	switch(r->r_ip_p) {
+	case IPPROTO_TCP:
+	{
+		register struct tcphdr *tcp;
+
+		/* verify that packet is not truncated */
+		if (CHECK_MLEN(*m, sizeof(struct tcphdr)))
+			ERROUT(EINVAL);
+
+		if (CHECK_PULLUP(*m, sizeof(struct tcphdr)))
+			ERROUT(ENOBUFS);
+
+		tcp = mtod(*m, struct tcphdr*);
+		r->r_sport = tcp->th_sport;
+		r->r_dport = tcp->th_dport;
+		*tcp_flags = tcp->th_flags;
+		break;
+	}
+	case IPPROTO_UDP:
+		/* verify that packet is not truncated */
+		if (CHECK_MLEN(*m, sizeof(struct udphdr)))
+			ERROUT(EINVAL);
+
+		if (CHECK_PULLUP(*m, sizeof(struct udphdr)))
+			ERROUT(ENOBUFS);
+
+		r->r_ports = *(mtod(*m, uint32_t *));
+		break;
+	}
+
+done:
+	return (error);
+}
+
+/*
+ * Non-static functions called from ng_netflow.c
+ */
+
+/* Allocate memory and set up flow cache */
+int
+ng_netflow_cache_init(priv_p priv)
+{
+	struct flow_entry *fle;
+	int i;
+
+	/* allocate cache */
+	MALLOC(priv->cache, struct flow_entry *,
+	    CACHESIZE * sizeof(struct flow_entry),
+	    M_NETFLOW, M_WAITOK | M_ZERO);
+
+	if (priv->cache == NULL)
+		return (ENOMEM);
+
+	/* allocate hash */
+	MALLOC(priv->hash, struct flow_hash_entry *,
+	    NBUCKETS * sizeof(struct flow_hash_entry),
+	    M_NETFLOW, M_WAITOK | M_ZERO);
+
+	if (priv->hash == NULL)
+		return (ENOMEM);
+
+	TAILQ_INIT(&priv->work_queue);
+	SLIST_INIT(&priv->free_list);
+	SLIST_INIT(&priv->expire_list);
+
+	mtx_init(&priv->work_mtx, "ng_netflow cache mutex", NULL, MTX_DEF);
+	mtx_init(&priv->free_mtx, "ng_netflow free mutex", NULL, MTX_DEF);
+	mtx_init(&priv->expire_mtx, "ng_netflow expire mutex", NULL, MTX_DEF);
+
+	/* build free list */
+	for (i = 0, fle = priv->cache; i < CACHESIZE; i++, fle++)
+		SLIST_INSERT_HEAD(&priv->free_list, fle, fle_free);
+
+	priv->info.nfinfo_free = CACHESIZE;
+
+	return (0);
+}
+
+/* Free all flow cache memory. Called from node close method. */
+void
+ng_netflow_cache_flush(priv_p priv)
+{
+	register struct flow_entry	*fle;
+	int i;
+
+	/*
+	 * We are going to free probably billable data.
+	 * Expire everything before freeing it.
+	 * No locking is required since callout is already drained.
+	 */
+
+	for (i = 0, fle = priv->cache; i < CACHESIZE; i++, fle++)
+		if (!ISFREE(fle))
+			/* ignore errors now */
+			(void )export_add(priv, fle);
+
+	mtx_destroy(&priv->work_mtx);
+	mtx_destroy(&priv->free_mtx);
+	mtx_destroy(&priv->expire_mtx);
+
+	/* free hash memory */
+	if (priv->hash)
+		FREE(priv->hash, M_NETFLOW);
+
+	/* free flow cache */
+	if (priv->cache)
+		FREE(priv->cache, M_NETFLOW);
+
+}
+
+/* Insert packet from &m into flow cache. */
+int
+ng_netflow_flow_add(priv_p priv, struct mbuf **m, iface_p iface)
+{
+	struct flow_hash_entry		*h = priv->hash;
+	register struct flow_entry	*fle;
+	struct flow_rec		r;
+	int			plen;
+	int			error = 1;
+	uint32_t		slot;
+	uint8_t			tcp_flags = 0;
+
+	priv->info.nfinfo_packets ++;
+
+	/* Try to fill *rec */
+	bzero(&r, sizeof(r));
+	if ((error = make_flow_rec(m, &plen, &r, &tcp_flags, iface->info.ifinfo_index)))
+		return (error);
+
+	slot = ip_hash(&r);
+
+	mtx_lock(&priv->work_mtx);
+	fle = hash_lookup(h, slot, &r); /* New flow entry or existent? */
+
+	if (fle) {	/* an existent entry */
+
+		TAILQ_REMOVE(&priv->work_queue, fle, fle_work);
+
+		fle->f.bytes += plen;
+		fle->f.packets ++;
+		fle->f.tcp_flags |= tcp_flags;
+		fle->f.last = time_uptime;
+
+		/*
+		 * We have the following reasons to expire flow in active way:
+		 * - it hit active timeout
+		 * - a TCP connection closed
+		 * - it is going to overflow counter
+		 */
+		if (tcp_flags & TH_FIN || tcp_flags & TH_RST || AGED(fle) ||
+		    (fle->f.bytes >= (UINT_MAX - IF_MAXMTU)) )
+			expire_flow(priv, fle);
+		else
+			TAILQ_INSERT_TAIL(&priv->work_queue, fle, fle_work);
+
+		mtx_unlock(&priv->work_mtx);
+		priv->info.nfinfo_bytes += plen;
+
+	} else {	/* a new flow entry */
+
+		mtx_unlock(&priv->work_mtx);
+		return hash_insert(priv, slot, &r, plen);
+
+	}
+
+	mtx_assert(&priv->work_mtx, MA_NOTOWNED);
+	mtx_assert(&priv->expire_mtx, MA_NOTOWNED);
+	mtx_assert(&priv->free_mtx, MA_NOTOWNED);
+	return (0);
+}
+
+/*
+ * Return records from cache. netgraph(4) guarantees us that we
+ * are locked against ng_netflow_rcvdata(). However we can
+ * work with ng_netflow_expire() in parrallel. XXX: Is it dangerous?
+ *
+ * TODO: matching particular IP should be done in kernel, here.
+ */
+int
+ng_netflow_flow_show(priv_p priv, uint32_t last, struct ng_mesg *resp)
+{
+	struct flow_entry *fle;
+	struct ngnf_flows *data;
+
+	data = (struct ngnf_flows *)resp->data;
+	data->last = 0;
+	data->nentries = 0;
+
+	/* Check if this is a first run */
+	if (last == 0)
+		fle = priv->cache;
+	else {
+		if (last > CACHESIZE-1)
+			return (EINVAL);
+		fle = priv->cache + last;
+	}
+
+	/*
+	 * We will transfer not more than NREC_AT_ONCE. More data
+	 * will come in next message.
+	 * We send current stop point to userland, and userland should return
+	 * it back to us.
+	 */
+	for (; last < CACHESIZE; fle++, last++) {
+		if (ISFREE(fle))
+			continue;
+		bcopy(&fle->f, &(data->entries[data->nentries]), sizeof(fle->f));
+		data->nentries ++;
+		if (data->nentries == NREC_AT_ONCE) {
+			if (++last < CACHESIZE)
+				data->last = (++fle - priv->cache);
+			return (0);
+		}
+     	}
+
+	return (0);
+}
+
+/* We have full datagram in privdata. Send it to export hook. */
+static int
+export_send(priv_p priv)
+{
+	struct netflow_v5_header *header = &priv->dgram.header;
+	struct timespec ts;
+	struct mbuf *m;
+	int error = 0;
+	int mlen;
+
+	header->sys_uptime = htonl(time_uptime);
+
+	getnanotime(&ts);
+	header->unix_secs  = htonl(ts.tv_sec);
+	header->unix_nsecs = htonl(ts.tv_nsec);
+
+	/* Flow sequence contains number of first record */
+	header->flow_seq = htonl(priv->flow_seq - header->count);
+
+	mlen = sizeof(struct netflow_v5_header) +
+	    sizeof(struct netflow_v5_record) * header->count;
+
+	header->count = htons(header->count);
+	if ((m = m_devget((caddr_t)header, mlen, 0, NULL, NULL)) == NULL) {
+		printf("ng_netflow: m_devget() failed, losing export dgram\n");
+		header->count = 0;
+		return(ENOBUFS);
+	}
+
+	header->count = 0;
+
+	/* Giant is required in sosend() at this moment. */
+	NET_LOCK_GIANT();
+	NG_SEND_DATA_ONLY(error, priv->export, m);
+	NET_UNLOCK_GIANT();
+
+	if (error)
+		NG_FREE_M(m);
+
+	return (error);
+}
+
+
+/* Create export datagram. */
+static int
+export_add(priv_p priv, struct flow_entry *fle)
+{
+	struct netflow_v5_header *header = &priv->dgram.header;
+	struct netflow_v5_record *rec;
+
+	if (header->count == 0 ) {	/* first record */
+		rec = &priv->dgram.r[0];
+		header->count = 1;
+	} else {			/* continue filling datagram */
+		rec = &priv->dgram.r[header->count];
+		header->count ++;
+	}
+
+	/* Fill in export record */
+	rec->src_addr = fle->f.r.r_src.s_addr;
+	rec->dst_addr = fle->f.r.r_dst.s_addr;
+	rec->next_hop = fle->f.next_hop.s_addr;
+	rec->i_ifx    = htons(fle->f.fle_i_ifx);
+	rec->o_ifx    = htons(fle->f.fle_o_ifx);
+	rec->packets  = htonl(fle->f.packets);
+	rec->octets   = htonl(fle->f.bytes);
+	rec->first    = htonl(fle->f.first);
+	rec->last     = htonl(fle->f.last);
+	rec->s_port   = fle->f.r.r_sport;
+	rec->d_port   = fle->f.r.r_dport;
+	rec->flags    = fle->f.tcp_flags;
+	rec->prot     = fle->f.r.r_ip_p;
+	rec->tos      = fle->f.r.r_tos;
+	rec->dst_mask = fle->f.dst_mask;
+	rec->src_mask = fle->f.src_mask;
+
+	priv->flow_seq++;
+
+	if (header->count == NETFLOW_V5_MAX_RECORDS) /* end of datagram */
+		return export_send(priv);
+
+	return (0);	
+}
+
+/* Periodic flow expiry run. */
+void
+ng_netflow_expire(void *arg)
+{
+	register struct flow_entry	*fle, *fle1;
+	priv_p priv = (priv_p )arg;
+	uint32_t used;
+	int error = 0;
+
+	/* First pack actively expired entries */
+	mtx_lock(&priv->expire_mtx);
+	while (!SLIST_EMPTY(&(priv->expire_list))) {
+		fle = SLIST_FIRST(&(priv->expire_list));
+		SLIST_REMOVE_HEAD(&(priv->expire_list), fle_free);
+		mtx_unlock(&priv->expire_mtx);
+
+		/*
+		 * While we have dropped the lock, expire_flow() may
+		 * insert another flow into top of the list.
+		 * This is not harmful for us, since we have already
+		 * detached our own.
+		 */
+
+		if ((error = export_add(priv, fle)) != 0)
+			printf("ng_netflow: export_add() failed: %u\n", error);
+		(void )free_flow(priv, fle);
+
+		mtx_lock(&priv->expire_mtx);
+	}
+	mtx_unlock(&priv->expire_mtx);
+
+	NGNF_GETUSED(priv, used);
+	mtx_lock(&priv->work_mtx);
+	TAILQ_FOREACH_SAFE(fle, &(priv->work_queue), fle_work, fle1) {
+		/*
+		 * When cache size has not reached CACHELOWAT yet, we keep both
+		 * inactive and active flows in cache. Doing this, we reduce number
+		 * of exports, since many inactive flows may wake up and continue
+		 * their life. However, we make an exclusion for scans. It is very
+		 * rare situation that inactive 1-packet flow will wake up.
+		 * When cache has reached CACHELOWAT, we expire all inactive flows,
+		 * until cache gets of sane size.
+		 * 
+		 * When this record's refcount is > 0, we skip it. (XXX)
+		 */
+		if (used <= CACHELOWAT && !INACTIVE(fle))
+			goto finish;
+
+		if (INACTIVE(fle) && (SMALL(fle) || (used > CACHELOWAT))) {
+
+			/* Detach flow entry from cache */
+			LIST_REMOVE(fle, fle_hash);
+			TAILQ_REMOVE(&priv->work_queue, fle, fle_work);
+
+			/*
+			 * While we are sending to collector, unlock cache.
+			 * XXX: it can happen, however with a small probability,
+			 * that item, we are holding now, can be moved to the top
+			 * of flow cache by node thread. In this case our expire
+			 * thread stops checking. Since this is not fatal we will
+			 * just ignore it now.
+			 */
+			mtx_unlock(&priv->work_mtx);
+
+			if ((error = export_add(priv, fle)) != 0)
+				printf("ng_netflow: export_add() failed: %u\n",
+				    error);
+
+			used = free_flow(priv, fle);
+
+			mtx_lock(&priv->work_mtx);
+		}
+     	}
+
+finish:
+	mtx_unlock(&priv->work_mtx);
+
+	mtx_assert(&priv->expire_mtx, MA_NOTOWNED);
+	mtx_assert(&priv->free_mtx, MA_NOTOWNED);
+
+	/* schedule next expire */
+	callout_reset(&priv->exp_callout, (1*hz), &ng_netflow_expire,
+	    (void *)priv);
+
+}