sched: CHOKe flow scheduler

CHOKe ("CHOose and Kill" or "CHOose and Keep") is an alternative
packet scheduler based on the Random Exponential Drop (RED) algorithm.

The core idea is:
  For every packet arrival:
  	Calculate Qave
	if (Qave < minth)
	     Queue the new packet
	else
	     Select randomly a packet from the queue
	     if (both packets from same flow)
	     then Drop both the packets
	     else if (Qave > maxth)
	          Drop packet
	     else
	       	  Admit packet with proability p (same as RED)

See also:
  Rong Pan, Balaji Prabhakar, Konstantinos Psounis, "CHOKe: a stateless active
   queue management scheme for approximating fair bandwidth allocation",
  Proceeding of INFOCOM'2000, March 2000.

Help from:
     Eric Dumazet <eric.dumazet@gmail.com>
     Patrick McHardy <kaber@trash.net>

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 689 insertions, 0 deletions

diff --git a/net/sched/Kconfig b/net/sched/Kconfig
index e318f458713..8c19b6e3201 100644
--- a/net/sched/Kconfig
+++ b/net/sched/Kconfig
@@ -217,6 +217,17 @@ config NET_SCH_MQPRIO
 
 	  If unsure, say N.
 
+config NET_SCH_CHOKE
+	tristate "CHOose and Keep responsive flow scheduler (CHOKE)"
+	help
+	  Say Y here if you want to use the CHOKe packet scheduler (CHOose
+	  and Keep for responsive flows, CHOose and Kill for unresponsive
+	  flows). This is a variation of RED which trys to penalize flows
+	  that monopolize the queue.
+
+	  To compile this code as a module, choose M here: the
+	  module will be called sch_choke.
+
 config NET_SCH_INGRESS
 	tristate "Ingress Qdisc"
 	depends on NET_CLS_ACT
diff --git a/net/sched/Makefile b/net/sched/Makefile
index 26ce681a2c6..06c6cdfd194 100644
--- a/net/sched/Makefile
+++ b/net/sched/Makefile
@@ -33,6 +33,8 @@ obj-$(CONFIG_NET_SCH_ATM)	+= sch_atm.o
 obj-$(CONFIG_NET_SCH_NETEM)	+= sch_netem.o
 obj-$(CONFIG_NET_SCH_DRR)	+= sch_drr.o
 obj-$(CONFIG_NET_SCH_MQPRIO)	+= sch_mqprio.o
+obj-$(CONFIG_NET_SCH_CHOKE)	+= sch_choke.o
+
 obj-$(CONFIG_NET_CLS_U32)	+= cls_u32.o
 obj-$(CONFIG_NET_CLS_ROUTE4)	+= cls_route.o
 obj-$(CONFIG_NET_CLS_FW)	+= cls_fw.o
diff --git a/net/sched/sch_choke.c b/net/sched/sch_choke.c
new file mode 100644
index 00000000000..a1cec18dd49
--- /dev/null
+++ b/net/sched/sch_choke.c
@@ -0,0 +1,676 @@
+/*
+ * net/sched/sch_choke.c	CHOKE scheduler
+ *
+ * Copyright (c) 2011 Stephen Hemminger <shemminger@vyatta.com>
+ * Copyright (c) 2011 Eric Dumazet <eric.dumazet@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * version 2 as published by the Free Software Foundation.
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/skbuff.h>
+#include <linux/reciprocal_div.h>
+#include <net/pkt_sched.h>
+#include <net/inet_ecn.h>
+#include <net/red.h>
+#include <linux/ip.h>
+#include <net/ip.h>
+#include <linux/ipv6.h>
+#include <net/ipv6.h>
+
+/*
+   CHOKe stateless AQM for fair bandwidth allocation
+   =================================================
+
+   CHOKe (CHOose and Keep for responsive flows, CHOose and Kill for
+   unresponsive flows) is a variant of RED that penalizes misbehaving flows but
+   maintains no flow state. The difference from RED is an additional step
+   during the enqueuing process. If average queue size is over the
+   low threshold (qmin), a packet is chosen at random from the queue.
+   If both the new and chosen packet are from the same flow, both
+   are dropped. Unlike RED, CHOKe is not really a "classful" qdisc because it
+   needs to access packets in queue randomly. It has a minimal class
+   interface to allow overriding the builtin flow classifier with
+   filters.
+
+   Source:
+   R. Pan, B. Prabhakar, and K. Psounis, "CHOKe, A Stateless
+   Active Queue Management Scheme for Approximating Fair Bandwidth Allocation",
+   IEEE INFOCOM, 2000.
+
+   A. Tang, J. Wang, S. Low, "Understanding CHOKe: Throughput and Spatial
+   Characteristics", IEEE/ACM Transactions on Networking, 2004
+
+ */
+
+/* Upper bound on size of sk_buff table (packets) */
+#define CHOKE_MAX_QUEUE	(128*1024 - 1)
+
+struct choke_sched_data {
+/* Parameters */
+	u32		 limit;
+	unsigned char	 flags;
+
+	struct red_parms parms;
+
+/* Variables */
+	struct tcf_proto *filter_list;
+	struct {
+		u32	prob_drop;	/* Early probability drops */
+		u32	prob_mark;	/* Early probability marks */
+		u32	forced_drop;	/* Forced drops, qavg > max_thresh */
+		u32	forced_mark;	/* Forced marks, qavg > max_thresh */
+		u32	pdrop;          /* Drops due to queue limits */
+		u32	other;          /* Drops due to drop() calls */
+		u32	matched;	/* Drops to flow match */
+	} stats;
+
+	unsigned int	 head;
+	unsigned int	 tail;
+
+	unsigned int	 tab_mask; /* size - 1 */
+
+	struct sk_buff **tab;
+};
+
+/* deliver a random number between 0 and N - 1 */
+static u32 random_N(unsigned int N)
+{
+	return reciprocal_divide(random32(), N);
+}
+
+/* number of elements in queue including holes */
+static unsigned int choke_len(const struct choke_sched_data *q)
+{
+	return (q->tail - q->head) & q->tab_mask;
+}
+
+/* Is ECN parameter configured */
+static int use_ecn(const struct choke_sched_data *q)
+{
+	return q->flags & TC_RED_ECN;
+}
+
+/* Should packets over max just be dropped (versus marked) */
+static int use_harddrop(const struct choke_sched_data *q)
+{
+	return q->flags & TC_RED_HARDDROP;
+}
+
+/* Move head pointer forward to skip over holes */
+static void choke_zap_head_holes(struct choke_sched_data *q)
+{
+	do {
+		q->head = (q->head + 1) & q->tab_mask;
+		if (q->head == q->tail)
+			break;
+	} while (q->tab[q->head] == NULL);
+}
+
+/* Move tail pointer backwards to reuse holes */
+static void choke_zap_tail_holes(struct choke_sched_data *q)
+{
+	do {
+		q->tail = (q->tail - 1) & q->tab_mask;
+		if (q->head == q->tail)
+			break;
+	} while (q->tab[q->tail] == NULL);
+}
+
+/* Drop packet from queue array by creating a "hole" */
+static void choke_drop_by_idx(struct Qdisc *sch, unsigned int idx)
+{
+	struct choke_sched_data *q = qdisc_priv(sch);
+	struct sk_buff *skb = q->tab[idx];
+
+	q->tab[idx] = NULL;
+
+	if (idx == q->head)
+		choke_zap_head_holes(q);
+	if (idx == q->tail)
+		choke_zap_tail_holes(q);
+
+	sch->qstats.backlog -= qdisc_pkt_len(skb);
+	qdisc_drop(skb, sch);
+	qdisc_tree_decrease_qlen(sch, 1);
+	--sch->q.qlen;
+}
+
+/*
+ * Compare flow of two packets
+ *  Returns true only if source and destination address and port match.
+ *          false for special cases
+ */
+static bool choke_match_flow(struct sk_buff *skb1,
+			     struct sk_buff *skb2)
+{
+	int off1, off2, poff;
+	const u32 *ports1, *ports2;
+	u8 ip_proto;
+	__u32 hash1;
+
+	if (skb1->protocol != skb2->protocol)
+		return false;
+
+	/* Use hash value as quick check
+	 * Assumes that __skb_get_rxhash makes IP header and ports linear
+	 */
+	hash1 = skb_get_rxhash(skb1);
+	if (!hash1 || hash1 != skb_get_rxhash(skb2))
+		return false;
+
+	/* Probably match, but be sure to avoid hash collisions */
+	off1 = skb_network_offset(skb1);
+	off2 = skb_network_offset(skb2);
+
+	switch (skb1->protocol) {
+	case __constant_htons(ETH_P_IP): {
+		const struct iphdr *ip1, *ip2;
+
+		ip1 = (const struct iphdr *) (skb1->data + off1);
+		ip2 = (const struct iphdr *) (skb2->data + off2);
+
+		ip_proto = ip1->protocol;
+		if (ip_proto != ip2->protocol ||
+		    ip1->saddr != ip2->saddr || ip1->daddr != ip2->daddr)
+			return false;
+
+		if ((ip1->frag_off | ip2->frag_off) & htons(IP_MF | IP_OFFSET))
+			ip_proto = 0;
+		off1 += ip1->ihl * 4;
+		off2 += ip2->ihl * 4;
+		break;
+	}
+
+	case __constant_htons(ETH_P_IPV6): {
+		const struct ipv6hdr *ip1, *ip2;
+
+		ip1 = (const struct ipv6hdr *) (skb1->data + off1);
+		ip2 = (const struct ipv6hdr *) (skb2->data + off2);
+
+		ip_proto = ip1->nexthdr;
+		if (ip_proto != ip2->nexthdr ||
+		    ipv6_addr_cmp(&ip1->saddr, &ip2->saddr) ||
+		    ipv6_addr_cmp(&ip1->daddr, &ip2->daddr))
+			return false;
+		off1 += 40;
+		off2 += 40;
+	}
+
+	default: /* Maybe compare MAC header here? */
+		return false;
+	}
+
+	poff = proto_ports_offset(ip_proto);
+	if (poff < 0)
+		return true;
+
+	off1 += poff;
+	off2 += poff;
+
+	ports1 = (__force u32 *)(skb1->data + off1);
+	ports2 = (__force u32 *)(skb2->data + off2);
+	return *ports1 == *ports2;
+}
+
+static inline void choke_set_classid(struct sk_buff *skb, u16 classid)
+{
+	*(unsigned int *)(qdisc_skb_cb(skb)->data) = classid;
+}
+
+static u16 choke_get_classid(const struct sk_buff *skb)
+{
+	return *(unsigned int *)(qdisc_skb_cb(skb)->data);
+}
+
+/*
+ * Classify flow using either:
+ *  1. pre-existing classification result in skb
+ *  2. fast internal classification
+ *  3. use TC filter based classification
+ */
+static bool choke_classify(struct sk_buff *skb,
+			   struct Qdisc *sch, int *qerr)
+
+{
+	struct choke_sched_data *q = qdisc_priv(sch);
+	struct tcf_result res;
+	int result;
+
+	result = tc_classify(skb, q->filter_list, &res);
+	if (result >= 0) {
+#ifdef CONFIG_NET_CLS_ACT
+		switch (result) {
+		case TC_ACT_STOLEN:
+		case TC_ACT_QUEUED:
+			*qerr = NET_XMIT_SUCCESS | __NET_XMIT_STOLEN;
+		case TC_ACT_SHOT:
+			return false;
+		}
+#endif
+		choke_set_classid(skb, TC_H_MIN(res.classid));
+		return true;
+	}
+
+	return false;
+}
+
+/*
+ * Select a packet at random from queue
+ * HACK: since queue can have holes from previous deletion; retry several
+ *   times to find a random skb but then just give up and return the head
+ * Will return NULL if queue is empty (q->head == q->tail)
+ */
+static struct sk_buff *choke_peek_random(const struct choke_sched_data *q,
+					 unsigned int *pidx)
+{
+	struct sk_buff *skb;
+	int retrys = 3;
+
+	do {
+		*pidx = (q->head + random_N(choke_len(q))) & q->tab_mask;
+		skb = q->tab[*pidx];
+		if (skb)
+			return skb;
+	} while (--retrys > 0);
+
+	return q->tab[*pidx = q->head];
+}
+
+/*
+ * Compare new packet with random packet in queue
+ * returns true if matched and sets *pidx
+ */
+static bool choke_match_random(const struct choke_sched_data *q,
+			       struct sk_buff *nskb,
+			       unsigned int *pidx)
+{
+	struct sk_buff *oskb;
+
+	if (q->head == q->tail)
+		return false;
+
+	oskb = choke_peek_random(q, pidx);
+	if (q->filter_list)
+		return choke_get_classid(nskb) == choke_get_classid(oskb);
+
+	return choke_match_flow(oskb, nskb);
+}
+
+static int choke_enqueue(struct sk_buff *skb, struct Qdisc *sch)
+{
+	struct choke_sched_data *q = qdisc_priv(sch);
+	struct red_parms *p = &q->parms;
+	int ret = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
+
+	if (q->filter_list) {
+		/* If using external classifiers, get result and record it. */
+		if (!choke_classify(skb, sch, &ret))
+			goto other_drop;	/* Packet was eaten by filter */
+	}
+
+	/* Compute average queue usage (see RED) */
+	p->qavg = red_calc_qavg(p, sch->q.qlen);
+	if (red_is_idling(p))
+		red_end_of_idle_period(p);
+
+	/* Is queue small? */
+	if (p->qavg <= p->qth_min)
+		p->qcount = -1;
+	else {
+		unsigned int idx;
+
+		/* Draw a packet at random from queue and compare flow */
+		if (choke_match_random(q, skb, &idx)) {
+			q->stats.matched++;
+			choke_drop_by_idx(sch, idx);
+			goto congestion_drop;
+		}
+
+		/* Queue is large, always mark/drop */
+		if (p->qavg > p->qth_max) {
+			p->qcount = -1;
+
+			sch->qstats.overlimits++;
+			if (use_harddrop(q) || !use_ecn(q) ||
+			    !INET_ECN_set_ce(skb)) {
+				q->stats.forced_drop++;
+				goto congestion_drop;
+			}
+
+			q->stats.forced_mark++;
+		} else if (++p->qcount) {
+			if (red_mark_probability(p, p->qavg)) {
+				p->qcount = 0;
+				p->qR = red_random(p);
+
+				sch->qstats.overlimits++;
+				if (!use_ecn(q) || !INET_ECN_set_ce(skb)) {
+					q->stats.prob_drop++;
+					goto congestion_drop;
+				}
+
+				q->stats.prob_mark++;
+			}
+		} else
+			p->qR = red_random(p);
+	}
+
+	/* Admit new packet */
+	if (sch->q.qlen < q->limit) {
+		q->tab[q->tail] = skb;
+		q->tail = (q->tail + 1) & q->tab_mask;
+		++sch->q.qlen;
+		sch->qstats.backlog += qdisc_pkt_len(skb);
+		return NET_XMIT_SUCCESS;
+	}
+
+	q->stats.pdrop++;
+	sch->qstats.drops++;
+	kfree_skb(skb);
+	return NET_XMIT_DROP;
+
+ congestion_drop:
+	qdisc_drop(skb, sch);
+	return NET_XMIT_CN;
+
+ other_drop:
+	if (ret & __NET_XMIT_BYPASS)
+		sch->qstats.drops++;
+	kfree_skb(skb);
+	return ret;
+}
+
+static struct sk_buff *choke_dequeue(struct Qdisc *sch)
+{
+	struct choke_sched_data *q = qdisc_priv(sch);
+	struct sk_buff *skb;
+
+	if (q->head == q->tail) {
+		if (!red_is_idling(&q->parms))
+			red_start_of_idle_period(&q->parms);
+		return NULL;
+	}
+
+	skb = q->tab[q->head];
+	q->tab[q->head] = NULL;
+	choke_zap_head_holes(q);
+	--sch->q.qlen;
+	sch->qstats.backlog -= qdisc_pkt_len(skb);
+	qdisc_bstats_update(sch, skb);
+
+	return skb;
+}
+
+static unsigned int choke_drop(struct Qdisc *sch)
+{
+	struct choke_sched_data *q = qdisc_priv(sch);
+	unsigned int len;
+
+	len = qdisc_queue_drop(sch);
+	if (len > 0)
+		q->stats.other++;
+	else {
+		if (!red_is_idling(&q->parms))
+			red_start_of_idle_period(&q->parms);
+	}
+
+	return len;
+}
+
+static void choke_reset(struct Qdisc *sch)
+{
+	struct choke_sched_data *q = qdisc_priv(sch);
+
+	red_restart(&q->parms);
+}
+
+static const struct nla_policy choke_policy[TCA_CHOKE_MAX + 1] = {
+	[TCA_CHOKE_PARMS]	= { .len = sizeof(struct tc_red_qopt) },
+	[TCA_CHOKE_STAB]	= { .len = RED_STAB_SIZE },
+};
+
+
+static void choke_free(void *addr)
+{
+	if (addr) {
+		if (is_vmalloc_addr(addr))
+			vfree(addr);
+		else
+			kfree(addr);
+	}
+}
+
+static int choke_change(struct Qdisc *sch, struct nlattr *opt)
+{
+	struct choke_sched_data *q = qdisc_priv(sch);
+	struct nlattr *tb[TCA_CHOKE_MAX + 1];
+	const struct tc_red_qopt *ctl;
+	int err;
+	struct sk_buff **old = NULL;
+	unsigned int mask;
+
+	if (opt == NULL)
+		return -EINVAL;
+
+	err = nla_parse_nested(tb, TCA_CHOKE_MAX, opt, choke_policy);
+	if (err < 0)
+		return err;
+
+	if (tb[TCA_CHOKE_PARMS] == NULL ||
+	    tb[TCA_CHOKE_STAB] == NULL)
+		return -EINVAL;
+
+	ctl = nla_data(tb[TCA_CHOKE_PARMS]);
+
+	if (ctl->limit > CHOKE_MAX_QUEUE)
+		return -EINVAL;
+
+	mask = roundup_pow_of_two(ctl->limit + 1) - 1;
+	if (mask != q->tab_mask) {
+		struct sk_buff **ntab;
+
+		ntab = kcalloc(mask + 1, sizeof(struct sk_buff *), GFP_KERNEL);
+		if (!ntab)
+			ntab = vzalloc((mask + 1) * sizeof(struct sk_buff *));
+		if (!ntab)
+			return -ENOMEM;
+
+		sch_tree_lock(sch);
+		old = q->tab;
+		if (old) {
+			unsigned int oqlen = sch->q.qlen, tail = 0;
+
+			while (q->head != q->tail) {
+				struct sk_buff *skb = q->tab[q->head];
+
+				q->head = (q->head + 1) & q->tab_mask;
+				if (!skb)
+					continue;
+				if (tail < mask) {
+					ntab[tail++] = skb;
+					continue;
+				}
+				sch->qstats.backlog -= qdisc_pkt_len(skb);
+				--sch->q.qlen;
+				qdisc_drop(skb, sch);
+			}
+			qdisc_tree_decrease_qlen(sch, oqlen - sch->q.qlen);
+			q->head = 0;
+			q->tail = tail;
+		}
+
+		q->tab_mask = mask;
+		q->tab = ntab;
+	} else
+		sch_tree_lock(sch);
+
+	q->flags = ctl->flags;
+	q->limit = ctl->limit;
+
+	red_set_parms(&q->parms, ctl->qth_min, ctl->qth_max, ctl->Wlog,
+		      ctl->Plog, ctl->Scell_log,
+		      nla_data(tb[TCA_CHOKE_STAB]));
+
+	if (q->head == q->tail)
+		red_end_of_idle_period(&q->parms);
+
+	sch_tree_unlock(sch);
+	choke_free(old);
+	return 0;
+}
+
+static int choke_init(struct Qdisc *sch, struct nlattr *opt)
+{
+	return choke_change(sch, opt);
+}
+
+static int choke_dump(struct Qdisc *sch, struct sk_buff *skb)
+{
+	struct choke_sched_data *q = qdisc_priv(sch);
+	struct nlattr *opts = NULL;
+	struct tc_red_qopt opt = {
+		.limit		= q->limit,
+		.flags		= q->flags,
+		.qth_min	= q->parms.qth_min >> q->parms.Wlog,
+		.qth_max	= q->parms.qth_max >> q->parms.Wlog,
+		.Wlog		= q->parms.Wlog,
+		.Plog		= q->parms.Plog,
+		.Scell_log	= q->parms.Scell_log,
+	};
+
+	opts = nla_nest_start(skb, TCA_OPTIONS);
+	if (opts == NULL)
+		goto nla_put_failure;
+
+	NLA_PUT(skb, TCA_CHOKE_PARMS, sizeof(opt), &opt);
+	return nla_nest_end(skb, opts);
+
+nla_put_failure:
+	nla_nest_cancel(skb, opts);
+	return -EMSGSIZE;
+}
+
+static int choke_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
+{
+	struct choke_sched_data *q = qdisc_priv(sch);
+	struct tc_choke_xstats st = {
+		.early	= q->stats.prob_drop + q->stats.forced_drop,
+		.marked	= q->stats.prob_mark + q->stats.forced_mark,
+		.pdrop	= q->stats.pdrop,
+		.other	= q->stats.other,
+		.matched = q->stats.matched,
+	};
+
+	return gnet_stats_copy_app(d, &st, sizeof(st));
+}
+
+static void choke_destroy(struct Qdisc *sch)
+{
+	struct choke_sched_data *q = qdisc_priv(sch);
+
+	tcf_destroy_chain(&q->filter_list);
+	choke_free(q->tab);
+}
+
+static struct Qdisc *choke_leaf(struct Qdisc *sch, unsigned long arg)
+{
+	return NULL;
+}
+
+static unsigned long choke_get(struct Qdisc *sch, u32 classid)
+{
+	return 0;
+}
+
+static void choke_put(struct Qdisc *q, unsigned long cl)
+{
+}
+
+static unsigned long choke_bind(struct Qdisc *sch, unsigned long parent,
+				u32 classid)
+{
+	return 0;
+}
+
+static struct tcf_proto **choke_find_tcf(struct Qdisc *sch, unsigned long cl)
+{
+	struct choke_sched_data *q = qdisc_priv(sch);
+
+	if (cl)
+		return NULL;
+	return &q->filter_list;
+}
+
+static int choke_dump_class(struct Qdisc *sch, unsigned long cl,
+			  struct sk_buff *skb, struct tcmsg *tcm)
+{
+	tcm->tcm_handle |= TC_H_MIN(cl);
+	return 0;
+}
+
+static void choke_walk(struct Qdisc *sch, struct qdisc_walker *arg)
+{
+	if (!arg->stop) {
+		if (arg->fn(sch, 1, arg) < 0) {
+			arg->stop = 1;
+			return;
+		}
+		arg->count++;
+	}
+}
+
+static const struct Qdisc_class_ops choke_class_ops = {
+	.leaf		=	choke_leaf,
+	.get		=	choke_get,
+	.put		=	choke_put,
+	.tcf_chain	=	choke_find_tcf,
+	.bind_tcf	=	choke_bind,
+	.unbind_tcf	=	choke_put,
+	.dump		=	choke_dump_class,
+	.walk		=	choke_walk,
+};
+
+static struct sk_buff *choke_peek_head(struct Qdisc *sch)
+{
+	struct choke_sched_data *q = qdisc_priv(sch);
+
+	return (q->head != q->tail) ? q->tab[q->head] : NULL;
+}
+
+static struct Qdisc_ops choke_qdisc_ops __read_mostly = {
+	.id		=	"choke",
+	.priv_size	=	sizeof(struct choke_sched_data),
+
+	.enqueue	=	choke_enqueue,
+	.dequeue	=	choke_dequeue,
+	.peek		=	choke_peek_head,
+	.drop		=	choke_drop,
+	.init		=	choke_init,
+	.destroy	=	choke_destroy,
+	.reset		=	choke_reset,
+	.change		=	choke_change,
+	.dump		=	choke_dump,
+	.dump_stats	=	choke_dump_stats,
+	.owner		=	THIS_MODULE,
+};
+
+static int __init choke_module_init(void)
+{
+	return register_qdisc(&choke_qdisc_ops);
+}
+
+static void __exit choke_module_exit(void)
+{
+	unregister_qdisc(&choke_qdisc_ops);
+}
+
+module_init(choke_module_init)
+module_exit(choke_module_exit)
+
+MODULE_LICENSE("GPL");