Import the Statistical Information For TCP Research (SIFTR) kernel module into

FreeBSD. SIFTR logs a range of statistics on active TCP connections to a log
file, providing the ability to make highly granular measurements of TCP
connection state. The tool is aimed at system administrators, developers and
researchers alike. Please take it for a spin and test it out - the man page
should have all the information required to get you going.

Many thanks go to the Cisco University Research Program Fund at Community
Foundation Silicon Valley and the FreeBSD Foundation. Their support of our work
at the Centre for Advanced Internet Architectures, Swinburne University of
Technology is greatly appreciated.

Sponsored by:	Cisco URP, FreeBSD Foundation
Reviewed by:	dwmalone, gnn, rpaulo
Tested by:	Many on freebsd-current@ and elsewhere over the years
MFC after:	1 month

1 files changed, 1568 insertions, 0 deletions

diff --git a/sys/netinet/siftr.c b/sys/netinet/siftr.c
new file mode 100644
index 000000000000..f311ff316e24
--- /dev/null
+++ b/sys/netinet/siftr.c
@@ -0,0 +1,1568 @@
+/*-
+ * Copyright (c) 2007-2009, Centre for Advanced Internet Architectures
+ * Swinburne University of Technology, Melbourne, Australia
+ * (CRICOS number 00111D).
+ * Copyright (c) 2009-2010, The FreeBSD Foundation
+ * All rights reserved.
+ *
+ * Portions of this software were developed at the Centre for Advanced
+ * Internet Architectures, Swinburne University of Technology, Melbourne,
+ * Australia by Lawrence Stewart under sponsorship from the FreeBSD Foundation.
+ *
+ * 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.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHORS 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 AUTHORS 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.
+ */
+
+/******************************************************
+ * Statistical Information For TCP Research (SIFTR)
+ *
+ * A FreeBSD kernel module that adds very basic intrumentation to the
+ * TCP stack, allowing internal stats to be recorded to a log file
+ * for experimental, debugging and performance analysis purposes.
+ *
+ * SIFTR was first released in 2007 by James Healy and Lawrence Stewart whilst
+ * working on the NewTCP research project at Swinburne University's Centre for
+ * Advanced Internet Architectures, Melbourne, Australia, which was made
+ * possible in part by a grant from the Cisco University Research Program Fund
+ * at Community Foundation Silicon Valley. More details are available at:
+ *   http://caia.swin.edu.au/urp/newtcp/
+ *
+ * Work on SIFTR v1.2.x was sponsored by the FreeBSD Foundation as part of
+ * the "Enhancing the FreeBSD TCP Implementation" project 2008-2009.
+ * More details are available at:
+ *   http://www.freebsdfoundation.org/
+ *   http://caia.swin.edu.au/freebsd/etcp09/
+ *
+ * Lawrence Stewart is the current maintainer, and all contact regarding
+ * SIFTR should be directed to him via email: lastewart@swin.edu.au
+ *
+ * Initial release date: June 2007
+ * Most recent update: June 2010
+ ******************************************************/
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+#include <sys/alq.h>
+#include <sys/errno.h>
+#include <sys/hash.h>
+#include <sys/kernel.h>
+#include <sys/kthread.h>
+#include <sys/lock.h>
+#include <sys/mbuf.h>
+#include <sys/module.h>
+#include <sys/mutex.h>
+#include <sys/pcpu.h>
+#include <sys/proc.h>
+#include <sys/sbuf.h>
+#include <sys/smp.h>
+#include <sys/socket.h>
+#include <sys/socketvar.h>
+#include <sys/sysctl.h>
+#include <sys/unistd.h>
+
+#include <net/if.h>
+#include <net/pfil.h>
+
+#include <netinet/in.h>
+#include <netinet/in_pcb.h>
+#include <netinet/in_systm.h>
+#include <netinet/in_var.h>
+#include <netinet/ip.h>
+#include <netinet/tcp_var.h>
+
+#ifdef SIFTR_IPV6
+#include <netinet/ip6.h>
+#include <netinet6/in6_pcb.h>
+#endif /* SIFTR_IPV6 */
+
+#include <machine/in_cksum.h>
+
+/*
+ * Three digit version number refers to X.Y.Z where:
+ * X is the major version number
+ * Y is bumped to mark backwards incompatible changes
+ * Z is bumped to mark backwards compatible changes
+ */
+#define V_MAJOR		1
+#define V_BACKBREAK	2
+#define V_BACKCOMPAT	3
+#define MODVERSION	__CONCAT(V_MAJOR, __CONCAT(V_BACKBREAK, V_BACKCOMPAT))
+#define MODVERSION_STR	__XSTRING(V_MAJOR) "." __XSTRING(V_BACKBREAK) "." \
+    __XSTRING(V_BACKCOMPAT)
+
+#define HOOK 0
+#define UNHOOK 1
+#define SIFTR_EXPECTED_MAX_TCP_FLOWS 65536
+#define SYS_NAME "FreeBSD"
+#define PACKET_TAG_SIFTR 100
+#define PACKET_COOKIE_SIFTR 21749576
+#define SIFTR_LOG_FILE_MODE 0644
+#define SIFTR_DISABLE 0
+#define SIFTR_ENABLE 1
+
+/*
+ * Hard upper limit on the length of log messages. Bump this up if you add new
+ * data fields such that the line length could exceed the below value.
+ */
+#define MAX_LOG_MSG_LEN 200
+/* XXX: Make this a sysctl tunable. */
+#define SIFTR_ALQ_BUFLEN (1000*MAX_LOG_MSG_LEN)
+
+/*
+ * 1 byte for IP version
+ * IPv4: src/dst IP (4+4) + src/dst port (2+2) = 12 bytes
+ * IPv6: src/dst IP (16+16) + src/dst port (2+2) = 36 bytes
+ */
+#ifdef SIFTR_IPV6
+#define FLOW_KEY_LEN 37
+#else
+#define FLOW_KEY_LEN 13
+#endif
+
+#ifdef SIFTR_IPV6
+#define SIFTR_IPMODE 6
+#else
+#define SIFTR_IPMODE 4
+#endif
+
+/* useful macros */
+#define CAST_PTR_INT(X) (*((int*)(X)))
+
+#define UPPER_SHORT(X)	(((X) & 0xFFFF0000) >> 16)
+#define LOWER_SHORT(X)	((X) & 0x0000FFFF)
+
+#define FIRST_OCTET(X)	(((X) & 0xFF000000) >> 24)
+#define SECOND_OCTET(X)	(((X) & 0x00FF0000) >> 16)
+#define THIRD_OCTET(X)	(((X) & 0x0000FF00) >> 8)
+#define FOURTH_OCTET(X)	((X) & 0x000000FF)
+
+MALLOC_DECLARE(M_SIFTR);
+MALLOC_DEFINE(M_SIFTR, "siftr", "dynamic memory used by SIFTR");
+
+MALLOC_DECLARE(M_SIFTR_PKTNODE);
+MALLOC_DEFINE(M_SIFTR_PKTNODE, "siftr_pktnode", "SIFTR pkt_node struct");
+
+MALLOC_DECLARE(M_SIFTR_HASHNODE);
+MALLOC_DEFINE(M_SIFTR_HASHNODE, "siftr_hashnode", "SIFTR flow_hash_node struct");
+
+/* Used as links in the pkt manager queue. */
+struct pkt_node {
+	/* Timestamp of pkt as noted in the pfil hook. */
+	struct timeval		tval;
+	/* Direction pkt is travelling; either PFIL_IN or PFIL_OUT. */
+	uint8_t			direction;
+	/* IP version pkt_node relates to; either INP_IPV4 or INP_IPV6. */
+	uint8_t			ipver;
+	/* Hash of the pkt which triggered the log message. */
+	uint32_t		hash;
+	/* Local/foreign IP address. */
+#ifdef SIFTR_IPV6
+	uint32_t		ip_laddr[4];
+	uint32_t		ip_faddr[4];
+#else
+	uint8_t			ip_laddr[4];
+	uint8_t			ip_faddr[4];
+#endif
+	/* Local TCP port. */
+	uint16_t		tcp_localport;
+	/* Foreign TCP port. */
+	uint16_t		tcp_foreignport;
+	/* Congestion Window (bytes). */
+	u_long			snd_cwnd;
+	/* Sending Window (bytes). */
+	u_long			snd_wnd;
+	/* Receive Window (bytes). */
+	u_long			rcv_wnd;
+	/* Bandwidth Controlled Window (bytes). */
+	u_long			snd_bwnd;
+	/* Slow Start Threshold (bytes). */
+	u_long			snd_ssthresh;
+	/* Current state of the TCP FSM. */
+	int			conn_state;
+	/* Max Segment Size (bytes). */
+	u_int			max_seg_size;
+	/*
+	 * Smoothed RTT stored as found in the TCP control block
+	 * in units of (TCP_RTT_SCALE*hz).
+	 */
+	int			smoothed_rtt;
+	/* Is SACK enabled? */
+	u_char			sack_enabled;
+	/* Window scaling for snd window. */
+	u_char			snd_scale;
+	/* Window scaling for recv window. */
+	u_char			rcv_scale;
+	/* TCP control block flags. */
+	u_int			flags;
+	/* Retransmit timeout length. */
+	int			rxt_length;
+	/* Size of the TCP send buffer in bytes. */
+	u_int			snd_buf_hiwater;
+	/* Current num bytes in the send socket buffer. */
+	u_int			snd_buf_cc;
+	/* Size of the TCP receive buffer in bytes. */
+	u_int			rcv_buf_hiwater;
+	/* Current num bytes in the receive socket buffer. */
+	u_int			rcv_buf_cc;
+	/* Number of bytes inflight that we are waiting on ACKs for. */
+	u_int			sent_inflight_bytes;
+	/* Link to next pkt_node in the list. */
+	STAILQ_ENTRY(pkt_node)	nodes;
+};
+
+struct flow_hash_node
+{
+	uint16_t counter;
+	uint8_t key[FLOW_KEY_LEN];
+	LIST_ENTRY(flow_hash_node) nodes;
+};
+
+struct siftr_stats
+{
+	/* # TCP pkts seen by the SIFTR PFIL hooks, including any skipped. */
+	uint64_t n_in;
+	uint64_t n_out;
+	/* # pkts skipped due to failed malloc calls. */
+	uint32_t nskip_in_malloc;
+	uint32_t nskip_out_malloc;
+	/* # pkts skipped due to failed mtx acquisition. */
+	uint32_t nskip_in_mtx;
+	uint32_t nskip_out_mtx;
+	/* # pkts skipped due to failed inpcb lookups. */
+	uint32_t nskip_in_inpcb;
+	uint32_t nskip_out_inpcb;
+	/* # pkts skipped due to failed tcpcb lookups. */
+	uint32_t nskip_in_tcpcb;
+	uint32_t nskip_out_tcpcb;
+	/* # pkts skipped due to stack reinjection. */
+	uint32_t nskip_in_dejavu;
+	uint32_t nskip_out_dejavu;
+};
+
+static DPCPU_DEFINE(struct siftr_stats, ss);
+
+static volatile unsigned int siftr_exit_pkt_manager_thread = 0;
+static unsigned int siftr_enabled = 0;
+static unsigned int siftr_pkts_per_log = 1;
+static unsigned int siftr_generate_hashes = 0;
+/* static unsigned int siftr_binary_log = 0; */
+static char siftr_logfile[PATH_MAX] = "/var/log/siftr.log";
+static u_long siftr_hashmask;
+STAILQ_HEAD(pkthead, pkt_node) pkt_queue = STAILQ_HEAD_INITIALIZER(pkt_queue);
+LIST_HEAD(listhead, flow_hash_node) *counter_hash;
+static int wait_for_pkt;
+static struct alq *siftr_alq = NULL;
+static struct mtx siftr_pkt_queue_mtx;
+static struct mtx siftr_pkt_mgr_mtx;
+static struct thread *siftr_pkt_manager_thr = NULL;
+/*
+ * pfil.h defines PFIL_IN as 1 and PFIL_OUT as 2,
+ * which we use as an index into this array.
+ */
+static char direction[3] = {'\0', 'i','o'};
+
+/* Required function prototypes. */
+static int siftr_sysctl_enabled_handler(SYSCTL_HANDLER_ARGS);
+static int siftr_sysctl_logfile_name_handler(SYSCTL_HANDLER_ARGS);
+
+
+/* Declare the net.inet.siftr sysctl tree and populate it. */
+
+SYSCTL_DECL(_net_inet_siftr);
+
+SYSCTL_NODE(_net_inet, OID_AUTO, siftr, CTLFLAG_RW, NULL,
+    "siftr related settings");
+
+SYSCTL_PROC(_net_inet_siftr, OID_AUTO, enabled, CTLTYPE_UINT|CTLFLAG_RW,
+    &siftr_enabled, 0, &siftr_sysctl_enabled_handler, "IU",
+    "switch siftr module operations on/off");
+
+SYSCTL_PROC(_net_inet_siftr, OID_AUTO, logfile, CTLTYPE_STRING|CTLFLAG_RW,
+    &siftr_logfile, sizeof(siftr_logfile), &siftr_sysctl_logfile_name_handler,
+    "A", "file to save siftr log messages to");
+
+SYSCTL_UINT(_net_inet_siftr, OID_AUTO, ppl, CTLFLAG_RW,
+    &siftr_pkts_per_log, 1,
+    "number of packets between generating a log message");
+
+SYSCTL_UINT(_net_inet_siftr, OID_AUTO, genhashes, CTLFLAG_RW,
+    &siftr_generate_hashes, 0,
+    "enable packet hash generation");
+
+/* XXX: TODO
+SYSCTL_UINT(_net_inet_siftr, OID_AUTO, binary, CTLFLAG_RW,
+    &siftr_binary_log, 0,
+    "write log files in binary instead of ascii");
+*/
+
+
+/* Begin functions. */
+
+static void
+siftr_process_pkt(struct pkt_node * pkt_node)
+{
+	struct flow_hash_node *hash_node;
+	struct listhead *counter_list;
+	struct siftr_stats *ss;
+	struct ale *log_buf;
+	uint8_t key[FLOW_KEY_LEN];
+	uint8_t found_match, key_offset;
+
+	hash_node = NULL;
+	ss = DPCPU_PTR(ss);
+	found_match = 0;
+	key_offset = 1;
+
+	/*
+	 * Create the key that will be used to create a hash index
+	 * into our hash table. Our key consists of:
+	 * ipversion, localip, localport, foreignip, foreignport
+	 */
+	key[0] = pkt_node->ipver;
+	memcpy(key + key_offset, &pkt_node->ip_laddr,
+	    sizeof(pkt_node->ip_laddr));
+	key_offset += sizeof(pkt_node->ip_laddr);
+	memcpy(key + key_offset, &pkt_node->tcp_localport,
+	    sizeof(pkt_node->tcp_localport));
+	key_offset += sizeof(pkt_node->tcp_localport);
+	memcpy(key + key_offset, &pkt_node->ip_faddr,
+	    sizeof(pkt_node->ip_faddr));
+	key_offset += sizeof(pkt_node->ip_faddr);
+	memcpy(key + key_offset, &pkt_node->tcp_foreignport,
+	    sizeof(pkt_node->tcp_foreignport));
+
+	counter_list = counter_hash +
+	    (hash32_buf(key, sizeof(key), 0) & siftr_hashmask);
+
+	/*
+	 * If the list is not empty i.e. the hash index has
+	 * been used by another flow previously.
+	 */
+	if (LIST_FIRST(counter_list) != NULL) {
+		/*
+		 * Loop through the hash nodes in the list.
+		 * There should normally only be 1 hash node in the list,
+		 * except if there have been collisions at the hash index
+		 * computed by hash32_buf().
+		 */
+		LIST_FOREACH(hash_node, counter_list, nodes) {
+			/*
+			 * Check if the key for the pkt we are currently
+			 * processing is the same as the key stored in the
+			 * hash node we are currently processing.
+			 * If they are the same, then we've found the
+			 * hash node that stores the counter for the flow
+			 * the pkt belongs to.
+			 */
+			if (memcmp(hash_node->key, key, sizeof(key)) == 0) {
+				found_match = 1;
+				break;
+			}
+		}
+	}
+
+	/* If this flow hash hasn't been seen before or we have a collision. */
+	if (hash_node == NULL || !found_match) {
+		/* Create a new hash node to store the flow's counter. */
+		hash_node = malloc(sizeof(struct flow_hash_node),
+		    M_SIFTR_HASHNODE, M_WAITOK);
+
+		if (hash_node != NULL) {
+			/* Initialise our new hash node list entry. */
+			hash_node->counter = 0;
+			memcpy(hash_node->key, key, sizeof(key));
+			LIST_INSERT_HEAD(counter_list, hash_node, nodes);
+		} else {
+			/* Malloc failed. */
+			if (pkt_node->direction == PFIL_IN)
+				ss->nskip_in_malloc++;
+			else
+				ss->nskip_out_malloc++;
+
+			return;
+		}
+	} else if (siftr_pkts_per_log > 1) {
+		/*
+		 * Taking the remainder of the counter divided
+		 * by the current value of siftr_pkts_per_log
+		 * and storing that in counter provides a neat
+		 * way to modulate the frequency of log
+		 * messages being written to the log file.
+		 */
+		hash_node->counter = (hash_node->counter + 1) %
+		    siftr_pkts_per_log;
+
+		/*
+		 * If we have not seen enough packets since the last time
+		 * we wrote a log message for this connection, return.
+		 */
+		if (hash_node->counter > 0)
+			return;
+	}
+
+	log_buf = alq_getn(siftr_alq, MAX_LOG_MSG_LEN, ALQ_WAITOK);
+
+	if (log_buf == NULL)
+		return; /* Should only happen if the ALQ is shutting down. */
+
+#ifdef SIFTR_IPV6
+	pkt_node->ip_laddr[3] = ntohl(pkt_node->ip_laddr[3]);
+	pkt_node->ip_faddr[3] = ntohl(pkt_node->ip_faddr[3]);
+
+	if (pkt_node->ipver == INP_IPV6) { /* IPv6 packet */
+		pkt_node->ip_laddr[0] = ntohl(pkt_node->ip_laddr[0]);
+		pkt_node->ip_laddr[1] = ntohl(pkt_node->ip_laddr[1]);
+		pkt_node->ip_laddr[2] = ntohl(pkt_node->ip_laddr[2]);
+		pkt_node->ip_faddr[0] = ntohl(pkt_node->ip_faddr[0]);
+		pkt_node->ip_faddr[1] = ntohl(pkt_node->ip_faddr[1]);
+		pkt_node->ip_faddr[2] = ntohl(pkt_node->ip_faddr[2]);
+
+		/* Construct an IPv6 log message. */
+		log_buf->ae_bytesused = snprintf(log_buf->ae_data,
+		    MAX_LOG_MSG_LEN,
+		    "%c,0x%08x,%zd.%06ld,%x:%x:%x:%x:%x:%x:%x:%x,%u,%x:%x:%x:"
+		    "%x:%x:%x:%x:%x,%u,%ld,%ld,%ld,%ld,%ld,%u,%u,%u,%u,%u,%u,"
+		    "%u,%d,%u,%u,%u,%u,%u\n",
+		    direction[pkt_node->direction],
+		    pkt_node->hash,
+		    pkt_node->tval.tv_sec,
+		    pkt_node->tval.tv_usec,
+		    UPPER_SHORT(pkt_node->ip_laddr[0]),
+		    LOWER_SHORT(pkt_node->ip_laddr[0]),
+		    UPPER_SHORT(pkt_node->ip_laddr[1]),
+		    LOWER_SHORT(pkt_node->ip_laddr[1]),
+		    UPPER_SHORT(pkt_node->ip_laddr[2]),
+		    LOWER_SHORT(pkt_node->ip_laddr[2]),
+		    UPPER_SHORT(pkt_node->ip_laddr[3]),
+		    LOWER_SHORT(pkt_node->ip_laddr[3]),
+		    ntohs(pkt_node->tcp_localport),
+		    UPPER_SHORT(pkt_node->ip_faddr[0]),
+		    LOWER_SHORT(pkt_node->ip_faddr[0]),
+		    UPPER_SHORT(pkt_node->ip_faddr[1]),
+		    LOWER_SHORT(pkt_node->ip_faddr[1]),
+		    UPPER_SHORT(pkt_node->ip_faddr[2]),
+		    LOWER_SHORT(pkt_node->ip_faddr[2]),
+		    UPPER_SHORT(pkt_node->ip_faddr[3]),
+		    LOWER_SHORT(pkt_node->ip_faddr[3]),
+		    ntohs(pkt_node->tcp_foreignport),
+		    pkt_node->snd_ssthresh,
+		    pkt_node->snd_cwnd,
+		    pkt_node->snd_bwnd,
+		    pkt_node->snd_wnd,
+		    pkt_node->rcv_wnd,
+		    pkt_node->snd_scale,
+		    pkt_node->rcv_scale,
+		    pkt_node->conn_state,
+		    pkt_node->max_seg_size,
+		    pkt_node->smoothed_rtt,
+		    pkt_node->sack_enabled,
+		    pkt_node->flags,
+		    pkt_node->rxt_length,
+		    pkt_node->snd_buf_hiwater,
+		    pkt_node->snd_buf_cc,
+		    pkt_node->rcv_buf_hiwater,
+		    pkt_node->rcv_buf_cc,
+		    pkt_node->sent_inflight_bytes);
+	} else { /* IPv4 packet */
+		pkt_node->ip_laddr[0] = FIRST_OCTET(pkt_node->ip_laddr[3]);
+		pkt_node->ip_laddr[1] = SECOND_OCTET(pkt_node->ip_laddr[3]);
+		pkt_node->ip_laddr[2] = THIRD_OCTET(pkt_node->ip_laddr[3]);
+		pkt_node->ip_laddr[3] = FOURTH_OCTET(pkt_node->ip_laddr[3]);
+		pkt_node->ip_faddr[0] = FIRST_OCTET(pkt_node->ip_faddr[3]);
+		pkt_node->ip_faddr[1] = SECOND_OCTET(pkt_node->ip_faddr[3]);
+		pkt_node->ip_faddr[2] = THIRD_OCTET(pkt_node->ip_faddr[3]);
+		pkt_node->ip_faddr[3] = FOURTH_OCTET(pkt_node->ip_faddr[3]);
+#endif /* SIFTR_IPV6 */
+
+		/* Construct an IPv4 log message. */
+		log_buf->ae_bytesused = snprintf(log_buf->ae_data,
+		    MAX_LOG_MSG_LEN,
+		    "%c,0x%08x,%jd.%06ld,%u.%u.%u.%u,%u,%u.%u.%u.%u,%u,%ld,%ld,"
+		    "%ld,%ld,%ld,%u,%u,%u,%u,%u,%u,%u,%d,%u,%u,%u,%u,%u\n",
+		    direction[pkt_node->direction],
+		    pkt_node->hash,
+		    (intmax_t)pkt_node->tval.tv_sec,
+		    pkt_node->tval.tv_usec,
+		    pkt_node->ip_laddr[0],
+		    pkt_node->ip_laddr[1],
+		    pkt_node->ip_laddr[2],
+		    pkt_node->ip_laddr[3],
+		    ntohs(pkt_node->tcp_localport),
+		    pkt_node->ip_faddr[0],
+		    pkt_node->ip_faddr[1],
+		    pkt_node->ip_faddr[2],
+		    pkt_node->ip_faddr[3],
+		    ntohs(pkt_node->tcp_foreignport),
+		    pkt_node->snd_ssthresh,
+		    pkt_node->snd_cwnd,
+		    pkt_node->snd_bwnd,
+		    pkt_node->snd_wnd,
+		    pkt_node->rcv_wnd,
+		    pkt_node->snd_scale,
+		    pkt_node->rcv_scale,
+		    pkt_node->conn_state,
+		    pkt_node->max_seg_size,
+		    pkt_node->smoothed_rtt,
+		    pkt_node->sack_enabled,
+		    pkt_node->flags,
+		    pkt_node->rxt_length,
+		    pkt_node->snd_buf_hiwater,
+		    pkt_node->snd_buf_cc,
+		    pkt_node->rcv_buf_hiwater,
+		    pkt_node->rcv_buf_cc,
+		    pkt_node->sent_inflight_bytes);
+#ifdef SIFTR_IPV6
+	}
+#endif
+
+	alq_post_flags(siftr_alq, log_buf, 0);
+}
+
+
+static void
+siftr_pkt_manager_thread(void *arg)
+{
+	STAILQ_HEAD(pkthead, pkt_node) tmp_pkt_queue =
+	    STAILQ_HEAD_INITIALIZER(tmp_pkt_queue);
+	struct pkt_node *pkt_node, *pkt_node_temp;
+	uint8_t draining;
+
+	draining = 2;
+
+	mtx_lock(&siftr_pkt_mgr_mtx);
+
+	/* draining == 0 when queue has been flushed and it's safe to exit. */
+	while (draining) {
+		/*
+		 * Sleep until we are signalled to wake because thread has
+		 * been told to exit or until 1 tick has passed.
+		 */
+		mtx_sleep(&wait_for_pkt, &siftr_pkt_mgr_mtx, PWAIT, "pktwait",
+		    1);
+
+		/* Gain exclusive access to the pkt_node queue. */
+		mtx_lock(&siftr_pkt_queue_mtx);
+
+		/*
+		 * Move pkt_queue to tmp_pkt_queue, which leaves
+		 * pkt_queue empty and ready to receive more pkt_nodes.
+		 */
+		STAILQ_CONCAT(&tmp_pkt_queue, &pkt_queue);
+
+		/*
+		 * We've finished making changes to the list. Unlock it
+		 * so the pfil hooks can continue queuing pkt_nodes.
+		 */
+		mtx_unlock(&siftr_pkt_queue_mtx);
+
+		/*
+		 * We can't hold a mutex whilst calling siftr_process_pkt
+		 * because ALQ might sleep waiting for buffer space.
+		 */
+		mtx_unlock(&siftr_pkt_mgr_mtx);
+
+		/* Flush all pkt_nodes to the log file. */
+		STAILQ_FOREACH_SAFE(pkt_node, &tmp_pkt_queue, nodes,
+		    pkt_node_temp) {
+			siftr_process_pkt(pkt_node);
+			STAILQ_REMOVE_HEAD(&tmp_pkt_queue, nodes);
+			free(pkt_node, M_SIFTR_PKTNODE);
+		}
+
+		KASSERT(STAILQ_EMPTY(&tmp_pkt_queue),
+		    ("SIFTR tmp_pkt_queue not empty after flush"));
+
+		mtx_lock(&siftr_pkt_mgr_mtx);
+
+		/*
+		 * If siftr_exit_pkt_manager_thread gets set during the window
+		 * where we are draining the tmp_pkt_queue above, there might
+		 * still be pkts in pkt_queue that need to be drained.
+		 * Allow one further iteration to occur after
+		 * siftr_exit_pkt_manager_thread has been set to ensure
+		 * pkt_queue is completely empty before we kill the thread.
+		 *
+		 * siftr_exit_pkt_manager_thread is set only after the pfil
+		 * hooks have been removed, so only 1 extra iteration
+		 * is needed to drain the queue.
+		 */
+		if (siftr_exit_pkt_manager_thread)
+			draining--;
+	}
+
+	mtx_unlock(&siftr_pkt_mgr_mtx);
+
+	/* Calls wakeup on this thread's struct thread ptr. */
+	kthread_exit();
+}
+
+
+static uint32_t
+hash_pkt(struct mbuf *m, uint32_t offset)
+{
+	uint32_t hash;
+
+	hash = 0;
+
+	while (m != NULL && offset > m->m_len) {
+		/*
+		 * The IP packet payload does not start in this mbuf, so
+		 * need to figure out which mbuf it starts in and what offset
+		 * into the mbuf's data region the payload starts at.
+		 */
+		offset -= m->m_len;
+		m = m->m_next;
+	}
+
+	while (m != NULL) {
+		/* Ensure there is data in the mbuf */
+		if ((m->m_len - offset) > 0)
+			hash = hash32_buf(m->m_data + offset,
+			    m->m_len - offset, hash);
+
+		m = m->m_next;
+		offset = 0;
+        }
+
+	return (hash);
+}
+
+
+/*
+ * Check if a given mbuf has the SIFTR mbuf tag. If it does, log the fact that
+ * it's a reinjected packet and return. If it doesn't, tag the mbuf and return.
+ * Return value >0 means the caller should skip processing this mbuf.
+ */
+static inline int
+siftr_chkreinject(struct mbuf *m, int dir, struct siftr_stats *ss)
+{
+	if (m_tag_locate(m, PACKET_COOKIE_SIFTR, PACKET_TAG_SIFTR, NULL)
+	    != NULL) {
+		if (dir == PFIL_IN)
+			ss->nskip_in_dejavu++;
+		else
+			ss->nskip_out_dejavu++;
+
+		return (1);
+	} else {
+		struct m_tag *tag = m_tag_alloc(PACKET_COOKIE_SIFTR,
+		    PACKET_TAG_SIFTR, 0, M_NOWAIT);
+		if (tag == NULL) {
+			if (dir == PFIL_IN)
+				ss->nskip_in_malloc++;
+			else
+				ss->nskip_out_malloc++;
+
+			return (1);
+		}
+
+		m_tag_prepend(m, tag);
+	}
+
+	return (0);
+}
+
+
+/*
+ * Look up an inpcb for a packet. Return the inpcb pointer if found, or NULL
+ * otherwise.
+ */
+static inline struct inpcb *
+siftr_findinpcb(int ipver, struct ip *ip, struct mbuf *m, uint16_t sport,
+    uint16_t dport, int dir, struct siftr_stats *ss)
+{
+	struct inpcb *inp;
+
+	/* We need the tcbinfo lock. */
+	INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
+	INP_INFO_RLOCK(&V_tcbinfo);
+
+	if (dir == PFIL_IN)
+		inp = (ipver == INP_IPV4 ?
+		    in_pcblookup_hash(&V_tcbinfo, ip->ip_src, sport, ip->ip_dst,
+		    dport, 0, m->m_pkthdr.rcvif)
+		    :
+#ifdef SIFTR_IPV6
+		    in6_pcblookup_hash(&V_tcbinfo,
+		    &((struct ip6_hdr *)ip)->ip6_src, sport,
+		    &((struct ip6_hdr *)ip)->ip6_dst, dport, 0,
+		    m->m_pkthdr.rcvif)
+#else
+		    NULL
+#endif
+		    );
+
+	else
+		inp = (ipver == INP_IPV4 ?
+		    in_pcblookup_hash(&V_tcbinfo, ip->ip_dst, dport, ip->ip_src,
+		    sport, 0, m->m_pkthdr.rcvif)
+		    :
+#ifdef SIFTR_IPV6
+		    in6_pcblookup_hash(&V_tcbinfo,
+		    &((struct ip6_hdr *)ip)->ip6_dst, dport,
+		    &((struct ip6_hdr *)ip)->ip6_src, sport, 0,
+		    m->m_pkthdr.rcvif)
+#else
+		    NULL
+#endif
+		    );
+
+	/* If we can't find the inpcb, bail. */
+	if (inp == NULL) {
+		if (dir == PFIL_IN)
+			ss->nskip_in_inpcb++;
+		else
+			ss->nskip_out_inpcb++;
+
+		INP_INFO_RUNLOCK(&V_tcbinfo);
+	} else {
+		/* Acquire the inpcb lock. */
+		INP_UNLOCK_ASSERT(inp);
+		INP_RLOCK(inp);
+		INP_INFO_RUNLOCK(&V_tcbinfo);
+	}
+
+	return (inp);
+}
+
+
+/*
+ * pfil hook that is called for each IPv4 packet making its way through the
+ * stack in either direction.
+ * The pfil subsystem holds a non-sleepable mutex somewhere when
+ * calling our hook function, so we can't sleep at all.
+ * It's very important to use the M_NOWAIT flag with all function calls
+ * that support it so that they won't sleep, otherwise you get a panic.
+ */
+static int
+siftr_chkpkt(void *arg, struct mbuf **m, struct ifnet *ifp, int dir,
+    struct inpcb *inp)
+{
+	struct pkt_node *pkt_node;
+	struct ip *ip;
+	struct tcphdr *th;
+	struct tcpcb *tp;
+	struct siftr_stats *ss;
+	unsigned int ip_hl;
+	uint8_t inp_locally_locked;
+
+	inp_locally_locked = 0;
+	ss = DPCPU_PTR(ss);
+
+	/*
+	 * m_pullup is not required here because ip_{input|output}
+	 * already do the heavy lifting for us.
+	 */
+
+	ip = mtod(*m, struct ip *);
+
+	/* Only continue processing if the packet is TCP. */
+	if (ip->ip_p != IPPROTO_TCP)
+		goto ret;
+
+	/*
+	 * If a kernel subsystem reinjects packets into the stack, our pfil
+	 * hook will be called multiple times for the same packet.
+	 * Make sure we only process unique packets.
+	 */
+	if (siftr_chkreinject(*m, dir, ss))
+		goto ret;
+
+	if (dir == PFIL_IN)
+		ss->n_in++;
+	else
+		ss->n_out++;
+
+	/*
+	 * Create a tcphdr struct starting at the correct offset
+	 * in the IP packet. ip->ip_hl gives the ip header length
+	 * in 4-byte words, so multiply it to get the size in bytes.
+	 */
+	ip_hl = (ip->ip_hl << 2);
+	th = (struct tcphdr *)((caddr_t)ip + ip_hl);
+
+	/*
+	 * If the pfil hooks don't provide a pointer to the
+	 * inpcb, we need to find it ourselves and lock it.
+	 */
+	if (!inp) {
+		/* Find the corresponding inpcb for this pkt. */
+		inp = siftr_findinpcb(INP_IPV4, ip, *m, th->th_sport,
+		    th->th_dport, dir, ss);
+
+		if (inp == NULL)
+			goto ret;
+		else
+			inp_locally_locked = 1;
+	}
+
+	INP_LOCK_ASSERT(inp);
+
+	pkt_node = malloc(sizeof(struct pkt_node), M_SIFTR_PKTNODE,
+	    M_NOWAIT | M_ZERO);
+
+	if (pkt_node == NULL) {
+		if (dir == PFIL_IN)
+			ss->nskip_in_malloc++;
+		else
+			ss->nskip_out_malloc++;
+
+		goto inp_unlock;
+	}
+
+	/* Find the TCP control block that corresponds with this packet */
+	tp = intotcpcb(inp);
+
+	/*
+	 * If we can't find the TCP control block (happens occasionaly for a
+	 * packet sent during the shutdown phase of a TCP connection),
+	 * or we're in the timewait state, bail
+	 */
+	if (tp == NULL || inp->inp_flags & INP_TIMEWAIT) {
+		if (dir == PFIL_IN)
+			ss->nskip_in_tcpcb++;
+		else
+			ss->nskip_out_tcpcb++;
+
+		free(pkt_node, M_SIFTR_PKTNODE);
+		goto inp_unlock;
+	}
+
+	/* Fill in pkt_node data */
+#ifdef SIFTR_IPV6
+	pkt_node->ip_laddr[3] = inp->inp_laddr.s_addr;
+	pkt_node->ip_faddr[3] = inp->inp_faddr.s_addr;
+#else
+	*((uint32_t *)pkt_node->ip_laddr) = inp->inp_laddr.s_addr;
+	*((uint32_t *)pkt_node->ip_faddr) = inp->inp_faddr.s_addr;
+#endif
+	pkt_node->tcp_localport = inp->inp_lport;
+	pkt_node->tcp_foreignport = inp->inp_fport;
+	pkt_node->snd_cwnd = tp->snd_cwnd;
+	pkt_node->snd_wnd = tp->snd_wnd;
+	pkt_node->rcv_wnd = tp->rcv_wnd;
+	pkt_node->snd_bwnd = tp->snd_bwnd;
+	pkt_node->snd_ssthresh = tp->snd_ssthresh;
+	pkt_node->snd_scale = tp->snd_scale;
+	pkt_node->rcv_scale = tp->rcv_scale;
+	pkt_node->conn_state = tp->t_state;
+	pkt_node->max_seg_size = tp->t_maxseg;
+	pkt_node->smoothed_rtt = tp->t_srtt;
+	pkt_node->sack_enabled = (tp->t_flags & TF_SACK_PERMIT) != 0;
+	pkt_node->flags = tp->t_flags;
+	pkt_node->rxt_length = tp->t_rxtcur;
+	pkt_node->snd_buf_hiwater = inp->inp_socket->so_snd.sb_hiwat;
+	pkt_node->snd_buf_cc = inp->inp_socket->so_snd.sb_cc;
+	pkt_node->rcv_buf_hiwater = inp->inp_socket->so_rcv.sb_hiwat;
+	pkt_node->rcv_buf_cc = inp->inp_socket->so_rcv.sb_cc;
+	pkt_node->sent_inflight_bytes = tp->snd_max - tp->snd_una;
+
+	/* We've finished accessing the tcb so release the lock. */
+	if (inp_locally_locked)
+		INP_RUNLOCK(inp);
+
+	/* These are safe to access without the inp lock. */
+	pkt_node->ipver = INP_IPV4;
+	pkt_node->direction = dir;
+
+	/*
+	 * Significantly more accurate than using getmicrotime(), but slower!
+	 * Gives true microsecond resolution at the expense of a hit to
+	 * maximum pps throughput processing when SIFTR is loaded and enabled.
+	 */
+	microtime(&(pkt_node->tval));
+
+	if (siftr_generate_hashes) {
+		if ((*m)->m_pkthdr.csum_flags & CSUM_TCP) {
+			/*
+			 * For outbound packets, the TCP checksum isn't
+			 * calculated yet. This is a problem for our packet
+			 * hashing as the receiver will calc a different hash
+			 * to ours if we don't include the correct TCP checksum
+			 * in the bytes being hashed. To work around this
+			 * problem, we manually calc the TCP checksum here in
+			 * software. We unset the CSUM_TCP flag so the lower
+			 * layers don't recalc it.
+			 */
+			(*m)->m_pkthdr.csum_flags &= ~CSUM_TCP;
+
+			/*
+			 * Calculate the TCP checksum in software and assign
+			 * to correct TCP header field, which will follow the
+			 * packet mbuf down the stack. The trick here is that
+			 * tcp_output() sets th->th_sum to the checksum of the
+			 * pseudo header for us already. Because of the nature
+			 * of the checksumming algorithm, we can sum over the
+			 * entire IP payload (i.e. TCP header and data), which
+			 * will include the already calculated pseduo header
+			 * checksum, thus giving us the complete TCP checksum.
+			 *
+			 * To put it in simple terms, if checksum(1,2,3,4)=10,
+			 * then checksum(1,2,3,4,5) == checksum(10,5).
+			 * This property is what allows us to "cheat" and
+			 * checksum only the IP payload which has the TCP
+			 * th_sum field populated with the pseudo header's
+			 * checksum, and not need to futz around checksumming
+			 * pseudo header bytes and TCP header/data in one hit.
+			 * Refer to RFC 1071 for more info.
+			 *
+			 * NB: in_cksum_skip(struct mbuf *m, int len, int skip)
+			 * in_cksum_skip 2nd argument is NOT the number of
+			 * bytes to read from the mbuf at "skip" bytes offset
+			 * from the start of the mbuf (very counter intuitive!).
+			 * The number of bytes to read is calculated internally
+			 * by the function as len-skip i.e. to sum over the IP
+			 * payload (TCP header + data) bytes, it is INCORRECT
+			 * to call the function like this:
+			 * in_cksum_skip(at, ip->ip_len - offset, offset)
+			 * Rather, it should be called like this:
+			 * in_cksum_skip(at, ip->ip_len, offset)
+			 * which means read "ip->ip_len - offset" bytes from
+			 * the mbuf cluster "at" at offset "offset" bytes from
+			 * the beginning of the "at" mbuf's data pointer.
+			 */
+			th->th_sum = in_cksum_skip(*m, ip->ip_len, ip_hl);
+		}
+
+		/*
+		 * XXX: Having to calculate the checksum in software and then
+		 * hash over all bytes is really inefficient. Would be nice to
+		 * find a way to create the hash and checksum in the same pass
+		 * over the bytes.
+		 */
+		pkt_node->hash = hash_pkt(*m, ip_hl);
+	}
+
+	mtx_lock(&siftr_pkt_queue_mtx);
+	STAILQ_INSERT_TAIL(&pkt_queue, pkt_node, nodes);
+	mtx_unlock(&siftr_pkt_queue_mtx);
+	goto ret;
+
+inp_unlock:
+	if (inp_locally_locked)
+		INP_RUNLOCK(inp);
+
+ret:
+	/* Returning 0 ensures pfil will not discard the pkt */
+	return (0);
+}
+
+
+#ifdef SIFTR_IPV6
+static int
+siftr_chkpkt6(void *arg, struct mbuf **m, struct ifnet *ifp, int dir,
+    struct inpcb *inp)
+{
+	struct pkt_node *pkt_node;
+	struct ip6_hdr *ip6;
+	struct tcphdr *th;
+	struct tcpcb *tp;
+	struct siftr_stats *ss;
+	unsigned int ip6_hl;
+	uint8_t inp_locally_locked;
+
+	inp_locally_locked = 0;
+	ss = DPCPU_PTR(ss);
+
+	/*
+	 * m_pullup is not required here because ip6_{input|output}
+	 * already do the heavy lifting for us.
+	 */
+
+	ip6 = mtod(*m, struct ip6_hdr *);
+
+	/*
+	 * Only continue processing if the packet is TCP
+	 * XXX: We should follow the next header fields
+	 * as shown on Pg 6 RFC 2460, but right now we'll
+	 * only check pkts that have no extension headers.
+	 */
+	if (ip6->ip6_nxt != IPPROTO_TCP)
+		goto ret6;
+
+	/*
+	 * If a kernel subsystem reinjects packets into the stack, our pfil
+	 * hook will be called multiple times for the same packet.
+	 * Make sure we only process unique packets.
+	 */
+	if (siftr_chkreinject(*m, dir, ss))
+		goto ret6;
+
+	if (dir == PFIL_IN)
+		ss->n_in++;
+	else
+		ss->n_out++;
+
+	ip6_hl = sizeof(struct ip6_hdr);
+
+	/*
+	 * Create a tcphdr struct starting at the correct offset
+	 * in the ipv6 packet. ip->ip_hl gives the ip header length
+	 * in 4-byte words, so multiply it to get the size in bytes.
+	 */
+	th = (struct tcphdr *)((caddr_t)ip6 + ip6_hl);
+
+	/*
+	 * For inbound packets, the pfil hooks don't provide a pointer to the
+	 * inpcb, so we need to find it ourselves and lock it.
+	 */
+	if (!inp) {
+		/* Find the corresponding inpcb for this pkt. */
+		inp = siftr_findinpcb(INP_IPV6, (struct ip *)ip6, *m,
+		    th->th_sport, th->th_dport, dir, ss);
+
+		if (inp == NULL)
+			goto ret6;
+		else
+			inp_locally_locked = 1;
+	}
+
+	pkt_node = malloc(sizeof(struct pkt_node), M_SIFTR_PKTNODE,
+	    M_NOWAIT | M_ZERO);
+
+	if (pkt_node == NULL) {
+		if (dir == PFIL_IN)
+			ss->nskip_in_malloc++;
+		else
+			ss->nskip_out_malloc++;
+
+		goto inp_unlock6;
+	}
+
+	/* Find the TCP control block that corresponds with this packet. */
+	tp = intotcpcb(inp);
+
+	/*
+	 * If we can't find the TCP control block (happens occasionaly for a
+	 * packet sent during the shutdown phase of a TCP connection),
+	 * or we're in the timewait state, bail.
+	 */
+	if (tp == NULL || inp->inp_flags & INP_TIMEWAIT) {
+		if (dir == PFIL_IN)
+			ss->nskip_in_tcpcb++;
+		else
+			ss->nskip_out_tcpcb++;
+
+		free(pkt_node, M_SIFTR_PKTNODE);
+		goto inp_unlock6;
+	}
+
+	/* Fill in pkt_node data. */
+	pkt_node->ip_laddr[0] = inp->in6p_laddr.s6_addr32[0];
+	pkt_node->ip_laddr[1] = inp->in6p_laddr.s6_addr32[1];
+	pkt_node->ip_laddr[2] = inp->in6p_laddr.s6_addr32[2];
+	pkt_node->ip_laddr[3] = inp->in6p_laddr.s6_addr32[3];
+	pkt_node->ip_faddr[0] = inp->in6p_faddr.s6_addr32[0];
+	pkt_node->ip_faddr[1] = inp->in6p_faddr.s6_addr32[1];
+	pkt_node->ip_faddr[2] = inp->in6p_faddr.s6_addr32[2];
+	pkt_node->ip_faddr[3] = inp->in6p_faddr.s6_addr32[3];
+	pkt_node->tcp_localport = inp->inp_lport;
+	pkt_node->tcp_foreignport = inp->inp_fport;
+	pkt_node->snd_cwnd = tp->snd_cwnd;
+	pkt_node->snd_wnd = tp->snd_wnd;
+	pkt_node->rcv_wnd = tp->rcv_wnd;
+	pkt_node->snd_bwnd = tp->snd_bwnd;
+	pkt_node->snd_ssthresh = tp->snd_ssthresh;
+	pkt_node->snd_scale = tp->snd_scale;
+	pkt_node->rcv_scale = tp->rcv_scale;
+	pkt_node->conn_state = tp->t_state;
+	pkt_node->max_seg_size = tp->t_maxseg;
+	pkt_node->smoothed_rtt = tp->t_srtt;
+	pkt_node->sack_enabled = (tp->t_flags & TF_SACK_PERMIT) != 0;
+	pkt_node->flags = tp->t_flags;
+	pkt_node->rxt_length = tp->t_rxtcur;
+	pkt_node->snd_buf_hiwater = inp->inp_socket->so_snd.sb_hiwat;
+	pkt_node->snd_buf_cc = inp->inp_socket->so_snd.sb_cc;
+	pkt_node->rcv_buf_hiwater = inp->inp_socket->so_rcv.sb_hiwat;
+	pkt_node->rcv_buf_cc = inp->inp_socket->so_rcv.sb_cc;
+	pkt_node->sent_inflight_bytes = tp->snd_max - tp->snd_una;
+
+	/* We've finished accessing the tcb so release the lock. */
+	if (inp_locally_locked)
+		INP_RUNLOCK(inp);
+
+	/* These are safe to access without the inp lock. */
+	pkt_node->ipver = INP_IPV6;
+	pkt_node->direction = dir;
+
+	/*
+	 * Significantly more accurate than using getmicrotime(), but slower!
+	 * Gives true microsecond resolution at the expense of a hit to
+	 * maximum pps throughput processing when SIFTR is loaded and enabled.
+	 */
+	microtime(&(pkt_node->tval));
+
+	/* XXX: Figure out how to do hash calcs for IPv6 */
+
+	mtx_lock(&siftr_pkt_queue_mtx);
+	STAILQ_INSERT_TAIL(&pkt_queue, pkt_node, nodes);
+	mtx_unlock(&siftr_pkt_queue_mtx);
+	goto ret6;
+
+inp_unlock6:
+	if (inp_locally_locked)
+		INP_RUNLOCK(inp);
+
+ret6:
+	/* Returning 0 ensures pfil will not discard the pkt. */
+	return (0);
+}
+#endif /* #ifdef SIFTR_IPV6 */
+
+
+static int
+siftr_pfil(int action)
+{
+	struct pfil_head *pfh_inet = pfil_head_get(PFIL_TYPE_AF, AF_INET);
+#ifdef SIFTR_IPV6
+	struct pfil_head *pfh_inet6 = pfil_head_get(PFIL_TYPE_AF, AF_INET6);
+#endif
+
+	if (action == HOOK) {
+		pfil_add_hook(siftr_chkpkt, NULL,
+		    PFIL_IN | PFIL_OUT | PFIL_WAITOK, pfh_inet);
+#ifdef SIFTR_IPV6
+		pfil_add_hook(siftr_chkpkt6, NULL,
+		    PFIL_IN | PFIL_OUT | PFIL_WAITOK, pfh_inet6);
+#endif
+	} else if (action == UNHOOK) {
+		pfil_remove_hook(siftr_chkpkt, NULL,
+		    PFIL_IN | PFIL_OUT | PFIL_WAITOK, pfh_inet);
+#ifdef SIFTR_IPV6
+		pfil_remove_hook(siftr_chkpkt6, NULL,
+		    PFIL_IN | PFIL_OUT | PFIL_WAITOK, pfh_inet6);
+#endif
+	}
+
+	return (0);
+}
+
+
+static int
+siftr_sysctl_logfile_name_handler(SYSCTL_HANDLER_ARGS)
+{
+	struct alq *new_alq;
+	int error;
+
+	if (req->newptr == NULL)
+		goto skip;
+
+	/* If old filename and new filename are different. */
+	if (strncmp(siftr_logfile, (char *)req->newptr, PATH_MAX)) {
+
+		error = alq_open(&new_alq, req->newptr, curthread->td_ucred,
+		    SIFTR_LOG_FILE_MODE, SIFTR_ALQ_BUFLEN, 0);
+
+		/* Bail if unable to create new alq. */
+		if (error)
+			return (1);
+
+		/*
+		 * If disabled, siftr_alq == NULL so we simply close
+		 * the alq as we've proved it can be opened.
+		 * If enabled, close the existing alq and switch the old
+		 * for the new.
+		 */
+		if (siftr_alq == NULL)
+			alq_close(new_alq);
+		else {
+			alq_close(siftr_alq);
+			siftr_alq = new_alq;
+		}
+	}
+
+skip:
+	return (sysctl_handle_string(oidp, arg1, arg2, req));
+}
+
+
+static int
+siftr_manage_ops(uint8_t action)
+{
+	struct siftr_stats totalss;
+	struct timeval tval;
+	struct flow_hash_node *counter, *tmp_counter;
+	struct sbuf *s;
+	int i, key_index, ret, error;
+	uint32_t bytes_to_write, total_skipped_pkts;
+	uint16_t lport, fport;
+	uint8_t *key, ipver;
+
+#ifdef SIFTR_IPV6
+	uint32_t laddr[4];
+	uint32_t faddr[4];
+#else
+	uint8_t laddr[4];
+	uint8_t faddr[4];
+#endif
+
+	error = 0;
+	total_skipped_pkts = 0;
+
+	/* Init an autosizing sbuf that initially holds 200 chars. */
+	if ((s = sbuf_new(NULL, NULL, 200, SBUF_AUTOEXTEND)) == NULL)
+		return (-1);
+
+	if (action == SIFTR_ENABLE) {
+		/*
+		 * Create our alq
+		 * XXX: We should abort if alq_open fails!
+		 */
+		alq_open(&siftr_alq, siftr_logfile, curthread->td_ucred,
+		    SIFTR_LOG_FILE_MODE, SIFTR_ALQ_BUFLEN, 0);
+
+		STAILQ_INIT(&pkt_queue);
+
+		siftr_exit_pkt_manager_thread = 0;
+
+		ret = kthread_add(&siftr_pkt_manager_thread, NULL, NULL,
+		    &siftr_pkt_manager_thr, RFNOWAIT, 0,
+		    "siftr_pkt_manager_thr");
+
+		siftr_pfil(HOOK);
+
+		microtime(&tval);
+
+		sbuf_printf(s,
+		    "enable_time_secs=%jd\tenable_time_usecs=%06ld\t"
+		    "siftrver=%s\thz=%u\ttcp_rtt_scale=%u\tsysname=%s\t"
+		    "sysver=%u\tipmode=%u\n",
+		    (intmax_t)tval.tv_sec, tval.tv_usec, MODVERSION_STR, hz,
+		    TCP_RTT_SCALE, SYS_NAME, __FreeBSD_version, SIFTR_IPMODE);
+
+		sbuf_finish(s);
+		alq_writen(siftr_alq, sbuf_data(s), sbuf_len(s), ALQ_WAITOK);
+
+	} else if (action == SIFTR_DISABLE && siftr_pkt_manager_thr != NULL) {
+		/*
+		 * Remove the pfil hook functions. All threads currently in
+		 * the hook functions are allowed to exit before siftr_pfil()
+		 * returns.
+		 */
+		siftr_pfil(UNHOOK);
+
+		/* This will block until the pkt manager thread unlocks it. */
+		mtx_lock(&siftr_pkt_mgr_mtx);
+
+		/* Tell the pkt manager thread that it should exit now. */
+		siftr_exit_pkt_manager_thread = 1;
+
+		/*
+		 * Wake the pkt_manager thread so it realises that
+		 * siftr_exit_pkt_manager_thread == 1 and exits gracefully.
+		 * The wakeup won't be delivered until we unlock
+		 * siftr_pkt_mgr_mtx so this isn't racy.
+		 */
+		wakeup(&wait_for_pkt);
+
+		/* Wait for the pkt_manager thread to exit. */
+		mtx_sleep(siftr_pkt_manager_thr, &siftr_pkt_mgr_mtx, PWAIT,
+		    "thrwait", 0);
+
+		siftr_pkt_manager_thr = NULL;
+		mtx_unlock(&siftr_pkt_mgr_mtx);
+
+		totalss.n_in = DPCPU_SUM(ss, n_in);
+		totalss.n_out = DPCPU_SUM(ss, n_out);
+		totalss.nskip_in_malloc = DPCPU_SUM(ss, nskip_in_malloc);
+		totalss.nskip_out_malloc = DPCPU_SUM(ss, nskip_out_malloc);
+		totalss.nskip_in_mtx = DPCPU_SUM(ss, nskip_in_mtx);
+		totalss.nskip_out_mtx = DPCPU_SUM(ss, nskip_out_mtx);
+		totalss.nskip_in_tcpcb = DPCPU_SUM(ss, nskip_in_tcpcb);
+		totalss.nskip_out_tcpcb = DPCPU_SUM(ss, nskip_out_tcpcb);
+		totalss.nskip_in_inpcb = DPCPU_SUM(ss, nskip_in_inpcb);
+		totalss.nskip_out_inpcb = DPCPU_SUM(ss, nskip_out_inpcb);
+
+		total_skipped_pkts = totalss.nskip_in_malloc +
+		    totalss.nskip_out_malloc + totalss.nskip_in_mtx +
+		    totalss.nskip_out_mtx + totalss.nskip_in_tcpcb +
+		    totalss.nskip_out_tcpcb + totalss.nskip_in_inpcb +
+		    totalss.nskip_out_inpcb;
+
+		microtime(&tval);
+
+		sbuf_printf(s,
+		    "disable_time_secs=%jd\tdisable_time_usecs=%06ld\t"
+		    "num_inbound_tcp_pkts=%ju\tnum_outbound_tcp_pkts=%ju\t"
+		    "total_tcp_pkts=%ju\tnum_inbound_skipped_pkts_malloc=%u\t"
+		    "num_outbound_skipped_pkts_malloc=%u\t"
+		    "num_inbound_skipped_pkts_mtx=%u\t"
+		    "num_outbound_skipped_pkts_mtx=%u\t"
+		    "num_inbound_skipped_pkts_tcpcb=%u\t"
+		    "num_outbound_skipped_pkts_tcpcb=%u\t"
+		    "num_inbound_skipped_pkts_inpcb=%u\t"
+		    "num_outbound_skipped_pkts_inpcb=%u\t"
+		    "total_skipped_tcp_pkts=%u\tflow_list=",
+		    (intmax_t)tval.tv_sec,
+		    tval.tv_usec,
+		    (uintmax_t)totalss.n_in,
+		    (uintmax_t)totalss.n_out,
+		    (uintmax_t)(totalss.n_in + totalss.n_out),
+		    totalss.nskip_in_malloc,
+		    totalss.nskip_out_malloc,
+		    totalss.nskip_in_mtx,
+		    totalss.nskip_out_mtx,
+		    totalss.nskip_in_tcpcb,
+		    totalss.nskip_out_tcpcb,
+		    totalss.nskip_in_inpcb,
+		    totalss.nskip_out_inpcb,
+		    total_skipped_pkts);
+
+		/*
+		 * Iterate over the flow hash, printing a summary of each
+		 * flow seen and freeing any malloc'd memory.
+		 * The hash consists of an array of LISTs (man 3 queue).
+		 */
+		for (i = 0; i < siftr_hashmask; i++) {
+			LIST_FOREACH_SAFE(counter, counter_hash + i, nodes,
+			    tmp_counter) {
+				key = counter->key;
+				key_index = 1;
+
+				ipver = key[0];
+
+				memcpy(laddr, key + key_index, sizeof(laddr));
+				key_index += sizeof(laddr);
+				memcpy(&lport, key + key_index, sizeof(lport));
+				key_index += sizeof(lport);
+				memcpy(faddr, key + key_index, sizeof(faddr));
+				key_index += sizeof(faddr);
+				memcpy(&fport, key + key_index, sizeof(fport));
+
+#ifdef SIFTR_IPV6
+				laddr[3] = ntohl(laddr[3]);
+				faddr[3] = ntohl(faddr[3]);
+
+				if (ipver == INP_IPV6) {
+					laddr[0] = ntohl(laddr[0]);
+					laddr[1] = ntohl(laddr[1]);
+					laddr[2] = ntohl(laddr[2]);
+					faddr[0] = ntohl(faddr[0]);
+					faddr[1] = ntohl(faddr[1]);
+					faddr[2] = ntohl(faddr[2]);
+
+					sbuf_printf(s,
+					    "%x:%x:%x:%x:%x:%x:%x:%x;%u-"
+					    "%x:%x:%x:%x:%x:%x:%x:%x;%u,",
+					    UPPER_SHORT(laddr[0]),
+					    LOWER_SHORT(laddr[0]),
+					    UPPER_SHORT(laddr[1]),
+					    LOWER_SHORT(laddr[1]),
+					    UPPER_SHORT(laddr[2]),
+					    LOWER_SHORT(laddr[2]),
+					    UPPER_SHORT(laddr[3]),
+					    LOWER_SHORT(laddr[3]),
+					    ntohs(lport),
+					    UPPER_SHORT(faddr[0]),
+					    LOWER_SHORT(faddr[0]),
+					    UPPER_SHORT(faddr[1]),
+					    LOWER_SHORT(faddr[1]),
+					    UPPER_SHORT(faddr[2]),
+					    LOWER_SHORT(faddr[2]),
+					    UPPER_SHORT(faddr[3]),
+					    LOWER_SHORT(faddr[3]),
+					    ntohs(fport));
+				} else {
+					laddr[0] = FIRST_OCTET(laddr[3]);
+					laddr[1] = SECOND_OCTET(laddr[3]);
+					laddr[2] = THIRD_OCTET(laddr[3]);
+					laddr[3] = FOURTH_OCTET(laddr[3]);
+					faddr[0] = FIRST_OCTET(faddr[3]);
+					faddr[1] = SECOND_OCTET(faddr[3]);
+					faddr[2] = THIRD_OCTET(faddr[3]);
+					faddr[3] = FOURTH_OCTET(faddr[3]);
+#endif
+					sbuf_printf(s,
+					    "%u.%u.%u.%u;%u-%u.%u.%u.%u;%u,",
+					    laddr[0],
+					    laddr[1],
+					    laddr[2],
+					    laddr[3],
+					    ntohs(lport),
+					    faddr[0],
+					    faddr[1],
+					    faddr[2],
+					    faddr[3],
+					    ntohs(fport));
+#ifdef SIFTR_IPV6
+				}
+#endif
+
+				free(counter, M_SIFTR_HASHNODE);
+			}
+
+			LIST_INIT(counter_hash + i);
+		}
+
+		sbuf_printf(s, "\n");
+		sbuf_finish(s);
+
+		i = 0;
+		do {
+			bytes_to_write = min(SIFTR_ALQ_BUFLEN, sbuf_len(s)-i);
+			alq_writen(siftr_alq, sbuf_data(s)+i, bytes_to_write, ALQ_WAITOK);
+			i += bytes_to_write;
+		} while (i < sbuf_len(s));
+
+		alq_close(siftr_alq);
+		siftr_alq = NULL;
+	}
+
+	sbuf_delete(s);
+
+	/*
+	 * XXX: Should be using ret to check if any functions fail
+	 * and set error appropriately
+	 */
+
+	return (error);
+}
+
+
+static int
+siftr_sysctl_enabled_handler(SYSCTL_HANDLER_ARGS)
+{
+	if (req->newptr == NULL)
+		goto skip;
+
+	/* If the value passed in isn't 0 or 1, return an error. */
+	if (CAST_PTR_INT(req->newptr) != 0 && CAST_PTR_INT(req->newptr) != 1)
+		return (1);
+
+	/* If we are changing state (0 to 1 or 1 to 0). */
+	if (CAST_PTR_INT(req->newptr) != siftr_enabled )
+		if (siftr_manage_ops(CAST_PTR_INT(req->newptr))) {
+			siftr_manage_ops(SIFTR_DISABLE);
+			return (1);
+		}
+
+skip:
+	return (sysctl_handle_int(oidp, arg1, arg2, req));
+}
+
+
+static void
+siftr_shutdown_handler(void *arg)
+{
+	siftr_manage_ops(SIFTR_DISABLE);
+}
+
+
+/*
+ * Module is being unloaded or machine is shutting down. Take care of cleanup.
+ */
+static int
+deinit_siftr(void)
+{
+	/* Cleanup. */
+	siftr_manage_ops(SIFTR_DISABLE);
+	hashdestroy(counter_hash, M_SIFTR, siftr_hashmask);
+	mtx_destroy(&siftr_pkt_queue_mtx);
+	mtx_destroy(&siftr_pkt_mgr_mtx);
+
+	return (0);
+}
+
+
+/*
+ * Module has just been loaded into the kernel.
+ */
+static int
+init_siftr(void)
+{
+	EVENTHANDLER_REGISTER(shutdown_pre_sync, siftr_shutdown_handler, NULL,
+	    SHUTDOWN_PRI_FIRST);
+
+	/* Initialise our flow counter hash table. */
+	counter_hash = hashinit(SIFTR_EXPECTED_MAX_TCP_FLOWS, M_SIFTR,
+	    &siftr_hashmask);
+
+	mtx_init(&siftr_pkt_queue_mtx, "siftr_pkt_queue_mtx", NULL, MTX_DEF);
+	mtx_init(&siftr_pkt_mgr_mtx, "siftr_pkt_mgr_mtx", NULL, MTX_DEF);
+
+	/* Print message to the user's current terminal. */
+	uprintf("\nStatistical Information For TCP Research (SIFTR) %s\n"
+	    "          http://caia.swin.edu.au/urp/newtcp\n\n",
+	    MODVERSION_STR);
+
+	return (0);
+}
+
+
+/*
+ * This is the function that is called to load and unload the module.
+ * When the module is loaded, this function is called once with
+ * "what" == MOD_LOAD
+ * When the module is unloaded, this function is called twice with
+ * "what" = MOD_QUIESCE first, followed by "what" = MOD_UNLOAD second
+ * When the system is shut down e.g. CTRL-ALT-DEL or using the shutdown command,
+ * this function is called once with "what" = MOD_SHUTDOWN
+ * When the system is shut down, the handler isn't called until the very end
+ * of the shutdown sequence i.e. after the disks have been synced.
+ */
+static int
+siftr_load_handler(module_t mod, int what, void *arg)
+{
+	int ret;
+
+	switch (what) {
+	case MOD_LOAD:
+		ret = init_siftr();
+		break;
+
+	case MOD_QUIESCE:
+	case MOD_SHUTDOWN:
+		ret = deinit_siftr();
+		break;
+
+	case MOD_UNLOAD:
+		ret = 0;
+		break;
+
+	default:
+		ret = EINVAL;
+		break;
+	}
+
+	return (ret);
+}
+
+
+static moduledata_t siftr_mod = {
+	.name = "siftr",
+	.evhand = siftr_load_handler,
+};
+
+/*
+ * Param 1: name of the kernel module
+ * Param 2: moduledata_t struct containing info about the kernel module
+ *          and the execution entry point for the module
+ * Param 3: From sysinit_sub_id enumeration in /usr/include/sys/kernel.h
+ *          Defines the module initialisation order
+ * Param 4: From sysinit_elem_order enumeration in /usr/include/sys/kernel.h
+ *          Defines the initialisation order of this kld relative to others
+ *          within the same subsystem as defined by param 3
+ */
+DECLARE_MODULE(siftr, siftr_mod, SI_SUB_SMP, SI_ORDER_ANY);
+MODULE_DEPEND(siftr, alq, 1, 1, 1);
+MODULE_VERSION(siftr, MODVERSION);