--- - Add some helper hook points to the TCP stack. The hooks allow Khelp
---   modules to access inbound/outbound events and associated data for
---   established TCP connections. The hooks only run if at least one hook
---   function is registered for the hook point, ensuring the impact on the
---   stack is effectively nil when no TCP Khelp modules are loaded. struct
---   tcp_hhook_data is passed as contextual data to any registered Khelp module
---   hook functions.
---
--- - Add an OSD (Object Specific Data) pointer to struct tcpcb to allow Khelp
---   modules to associate per-connection data with the tcpcb.
---
--- In collaboration with:	David Hayes <dahayes at swin edu au> and
---				Grenville Armitage <garmitage at swin edu au>
--- Sponsored by:	FreeBSD Foundation
--- Reviewed by:	bz, others along the way
--- MFC after:		3 months
---
Index: sys/netinet/tcp_input.c
===================================================================
--- sys/netinet/tcp_input.c	(revision 216753)
+++ sys/netinet/tcp_input.c	(working copy)
@@ -54,6 +54,7 @@ __FBSDID("$FreeBSD$");
 
 #include <sys/param.h>
 #include <sys/kernel.h>
+#include <sys/hhook.h>
 #include <sys/malloc.h>
 #include <sys/mbuf.h>
 #include <sys/proc.h>		/* for proc0 declaration */
@@ -218,6 +219,8 @@ static void inline	cc_ack_received(struct tcpcb *t
 			    uint16_t type);
 static void inline	cc_conn_init(struct tcpcb *tp);
 static void inline	cc_post_recovery(struct tcpcb *tp, struct tcphdr *th);
+static void inline	hhook_run_tcp_est_in(struct tcpcb *tp,
+			    struct tcphdr *th, struct tcpopt *to);
 
 /*
  * Kernel module interface for updating tcpstat.  The argument is an index
@@ -234,6 +237,24 @@ kmod_tcpstat_inc(int statnum)
 }
 
 /*
+ * Wrapper for the TCP established input helper hook.
+ */
+static void inline
+hhook_run_tcp_est_in(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to)
+{
+	struct tcp_hhook_data hhook_data;
+
+	if (V_tcp_hhh[HHOOK_TCP_EST_IN]->hhh_nhooks > 0) {
+		hhook_data.tp = tp;
+		hhook_data.th = th;
+		hhook_data.to = to;
+
+		hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_IN], &hhook_data,
+		    tp->osd);
+	}
+}
+
+/*
  * CC wrapper hook functions
  */
 static void inline
@@ -1486,6 +1507,10 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th,
 							ticks - tp->t_rtttime);
 				}
 				acked = BYTES_THIS_ACK(tp, th);
+
+				/* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
+				hhook_run_tcp_est_in(tp, th, &to);
+
 				TCPSTAT_INC(tcps_rcvackpack);
 				TCPSTAT_ADD(tcps_rcvackbyte, acked);
 				sbdrop(&so->so_snd, acked);
@@ -2199,6 +2224,10 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th,
 		    ((to.to_flags & TOF_SACK) ||
 		     !TAILQ_EMPTY(&tp->snd_holes)))
 			tcp_sack_doack(tp, &to, th->th_ack);
+
+		/* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
+		hhook_run_tcp_est_in(tp, th, &to);
+
 		if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
 			if (tlen == 0 && tiwin == tp->snd_wnd) {
 				TCPSTAT_INC(tcps_rcvdupack);
Index: sys/netinet/tcp_subr.c
===================================================================
--- sys/netinet/tcp_subr.c	(revision 216753)
+++ sys/netinet/tcp_subr.c	(working copy)
@@ -41,7 +41,9 @@ __FBSDID("$FreeBSD$");
 #include <sys/param.h>
 #include <sys/systm.h>
 #include <sys/callout.h>
+#include <sys/hhook.h>
 #include <sys/kernel.h>
+#include <sys/khelp.h>
 #include <sys/sysctl.h>
 #include <sys/jail.h>
 #include <sys/malloc.h>
@@ -214,6 +216,8 @@ SYSCTL_INT(_net_inet_tcp, OID_AUTO, soreceive_stre
 VNET_DEFINE(uma_zone_t, sack_hole_zone);
 #define	V_sack_hole_zone		VNET(sack_hole_zone)
 
+VNET_DEFINE(struct hhook_head *, tcp_hhh[HHOOK_TCP_LAST+1]);
+
 static struct inpcb *tcp_notify(struct inpcb *, int);
 static void	tcp_isn_tick(void *);
 static char *	tcp_log_addr(struct in_conninfo *inc, struct tcphdr *th,
@@ -239,6 +243,7 @@ struct tcpcb_mem {
 	struct	tcpcb		tcb;
 	struct	tcp_timer	tt;
 	struct	cc_var		ccv;
+	struct	osd		osd;
 };
 
 static VNET_DEFINE(uma_zone_t, tcpcb_zone);
@@ -278,6 +283,13 @@ tcp_init(void)
 {
 	int hashsize;
 
+	if (hhook_head_register(HHOOK_TYPE_TCP, HHOOK_TCP_EST_IN,
+	    &V_tcp_hhh[HHOOK_TCP_EST_IN], HHOOK_NOWAIT|HHOOK_HEADISINVNET) != 0)
+		printf("%s: WARNING: unable to register helper hook\n", __func__);
+	if (hhook_head_register(HHOOK_TYPE_TCP, HHOOK_TCP_EST_OUT,
+	    &V_tcp_hhh[HHOOK_TCP_EST_OUT], HHOOK_NOWAIT|HHOOK_HEADISINVNET) != 0)
+		printf("%s: WARNING: unable to register helper hook\n", __func__);
+
 	hashsize = TCBHASHSIZE;
 	TUNABLE_INT_FETCH("net.inet.tcp.tcbhashsize", &hashsize);
 	if (!powerof2(hashsize)) {
@@ -661,6 +673,12 @@ tcp_newtcpcb(struct inpcb *inp)
 			return (NULL);
 		}
 
+	tp->osd = &tm->osd;
+	if (khelp_init_osd(HELPER_CLASS_TCP, tp->osd)) {
+		uma_zfree(V_tcpcb_zone, tm);
+		return (NULL);
+	}
+
 #ifdef VIMAGE
 	tp->t_vnet = inp->inp_vnet;
 #endif
@@ -894,6 +912,8 @@ tcp_discardcb(struct tcpcb *tp)
 	if (CC_ALGO(tp)->cb_destroy != NULL)
 		CC_ALGO(tp)->cb_destroy(tp->ccv);
 
+	khelp_destroy_osd(tp->osd);
+
 	CC_ALGO(tp) = NULL;
 	inp->inp_ppcb = NULL;
 	tp->t_inpcb = NULL;
Index: sys/netinet/tcp_var.h
===================================================================
--- sys/netinet/tcp_var.h	(revision 216753)
+++ sys/netinet/tcp_var.h	(working copy)
@@ -201,6 +201,7 @@ struct tcpcb {
 	int	t_bytes_acked;		/* # bytes acked during current RTT */
 	struct cc_algo	*cc_algo;	/* congestion control algorithm */
 	struct cc_var	*ccv;
+	struct osd	*osd;		/* storage for Khelp module data */
 
 	int	t_ispare;		/* explicit pad for 64bit alignment */
 	void	*t_pspare2[4];		/* 4 TBD */
@@ -501,6 +502,22 @@ struct	tcpstat {
 void	kmod_tcpstat_inc(int statnum);
 #define	KMOD_TCPSTAT_INC(name)						\
 	kmod_tcpstat_inc(offsetof(struct tcpstat, name) / sizeof(u_long))
+
+/*
+ * TCP specific helper hook point identifiers.
+ */
+#define	HHOOK_TCP_EST_IN		0
+#define	HHOOK_TCP_EST_OUT		1
+#define	HHOOK_TCP_LAST			HHOOK_TCP_EST_OUT
+
+struct tcp_hhook_data {
+	struct tcpcb *tp;
+	struct tcphdr *th;
+	struct tcpopt *to;
+	long len;
+	int tso;
+	tcp_seq  curack;
+};
 #endif
 
 /*
@@ -608,6 +625,9 @@ VNET_DECLARE(int, tcp_ecn_maxretries);
 #define	V_tcp_do_ecn		VNET(tcp_do_ecn)
 #define	V_tcp_ecn_maxretries	VNET(tcp_ecn_maxretries)
 
+VNET_DECLARE(struct hhook_head *, tcp_hhh[HHOOK_TCP_LAST+1]);
+#define	V_tcp_hhh		VNET(tcp_hhh)
+
 int	 tcp_addoptions(struct tcpopt *, u_char *);
 int	 tcp_ccalgounload(struct cc_algo *unload_algo);
 struct tcpcb *
Index: sys/netinet/tcp_output.c
===================================================================
--- sys/netinet/tcp_output.c	(revision 216753)
+++ sys/netinet/tcp_output.c	(working copy)
@@ -40,6 +40,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/param.h>
 #include <sys/systm.h>
 #include <sys/domain.h>
+#include <sys/hhook.h>
 #include <sys/kernel.h>
 #include <sys/lock.h>
 #include <sys/mbuf.h>
@@ -126,9 +127,33 @@ SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, sendbuf_m
 	&VNET_NAME(tcp_autosndbuf_max), 0,
 	"Max size of automatic send buffer");
 
+static void inline	hhook_run_tcp_est_out(struct tcpcb *tp,
+			    struct tcphdr *th, struct tcpopt *to,
+			    long len, int tso);
 static void inline	cc_after_idle(struct tcpcb *tp);
 
 /*
+ * Wrapper for the TCP established ouput helper hook.
+ */
+static void inline
+hhook_run_tcp_est_out(struct tcpcb *tp, struct tcphdr *th,
+    struct tcpopt *to, long len, int tso)
+{
+	struct tcp_hhook_data hhook_data;
+
+	if (V_tcp_hhh[HHOOK_TCP_EST_OUT]->hhh_nhooks > 0) {
+		hhook_data.tp = tp;
+		hhook_data.th = th;
+		hhook_data.to = to;
+		hhook_data.len = len;
+		hhook_data.tso = tso;
+
+		hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_OUT], &hhook_data,
+		    tp->osd);
+	}
+}
+
+/*
  * CC wrapper hook functions
  */
 static void inline
@@ -1134,6 +1159,9 @@ timer:
 			tp->snd_max = tp->snd_nxt + len;
 	}
 
+	/* Run HHOOK_TCP_ESTABLISHED_OUT helper hooks. */
+	hhook_run_tcp_est_out(tp, th, &to, len, tso);
+
 #ifdef TCPDEBUG
 	/*
 	 * Trace.