Allow carp(4) to be loaded as a kernel module. Follow precedent set by

bridge(4), lagg(4) etc. and make use of function pointers and
pf_proto_register() to hook carp into the network stack.

Currently, because of the uncertainty about whether the unload path is free
of race condition panics, unloads are disallowed by default.  Compiling with
CARPMOD_CAN_UNLOAD in CFLAGS removes this anti foot shooting measure.

This commit requires IP6PROTOSPACER, introduced in r211115.

Reviewed by:	bz, simon
Approved by:	ken (mentor)
MFC after:	2 weeks

3 files changed, 19 insertions, 40 deletions

diff --git a/sys/net/if.c b/sys/net/if.c
index da323cc..3c4ad16 100644
--- a/sys/net/if.c
+++ b/sys/net/if.c
@@ -33,7 +33,6 @@
 #include "opt_compat.h"
 #include "opt_inet6.h"
 #include "opt_inet.h"
-#include "opt_carp.h"
 #include "opt_ddb.h"
 
 #include <sys/param.h>
@@ -89,11 +88,6 @@
 #ifdef INET
 #include <netinet/if_ether.h>
 #endif
-#if defined(INET) || defined(INET6)
-#ifdef DEV_CARP
-#include <netinet/ip_carp.h>
-#endif
-#endif
 
 #include <security/mac/mac_framework.h>
 
@@ -130,6 +124,7 @@ SX_SYSINIT(ifdescr_sx, &ifdescr_sx, "ifnet descr");
 void	(*bstp_linkstate_p)(struct ifnet *ifp, int state);
 void	(*ng_ether_link_state_p)(struct ifnet *ifp, int state);
 void	(*lagg_linkstate_p)(struct ifnet *ifp, int state);
+void	(*carp_linkstate_p)(struct ifnet *ifp);
 
 struct mbuf *(*tbr_dequeue_ptr)(struct ifaltq *, int) = NULL;
 
@@ -1813,12 +1808,8 @@ if_unroute(struct ifnet *ifp, int flag, int fam)
 			pfctlinput(PRC_IFDOWN, ifa->ifa_addr);
 	ifp->if_qflush(ifp);
 
-#if defined(INET) || defined(INET6)
-#ifdef DEV_CARP
 	if (ifp->if_carp)
-		carp_carpdev_state(ifp->if_carp);
-#endif
-#endif
+		(*carp_linkstate_p)(ifp);
 	rt_ifmsg(ifp);
 }
 
@@ -1839,12 +1830,8 @@ if_route(struct ifnet *ifp, int flag, int fam)
 	TAILQ_FOREACH(ifa, &ifp->if_addrhead, ifa_link)
 		if (fam == PF_UNSPEC || (fam == ifa->ifa_addr->sa_family))
 			pfctlinput(PRC_IFUP, ifa->ifa_addr);
-#if defined(INET) || defined(INET6)
-#ifdef DEV_CARP
 	if (ifp->if_carp)
-		carp_carpdev_state(ifp->if_carp);
-#endif
-#endif
+		(*carp_linkstate_p)(ifp);
 	rt_ifmsg(ifp);
 #ifdef INET6
 	in6_if_up(ifp);
@@ -1887,12 +1874,8 @@ do_link_state_change(void *arg, int pending)
 	if ((ifp->if_type == IFT_ETHER || ifp->if_type == IFT_L2VLAN) &&
 	    IFP2AC(ifp)->ac_netgraph != NULL)
 		(*ng_ether_link_state_p)(ifp, link_state);
-#if defined(INET) || defined(INET6)
-#ifdef DEV_CARP
 	if (ifp->if_carp)
-		carp_carpdev_state(ifp->if_carp);
-#endif
-#endif
+		(*carp_linkstate_p)(ifp);
 	if (ifp->if_bridge) {
 		KASSERT(bstp_linkstate_p != NULL,("if_bridge bstp not loaded!"));
 		(*bstp_linkstate_p)(ifp, link_state);
diff --git a/sys/net/if_bridge.c b/sys/net/if_bridge.c
index 5f33dd5..fb04731 100644
--- a/sys/net/if_bridge.c
+++ b/sys/net/if_bridge.c
@@ -79,7 +79,6 @@ __FBSDID("$FreeBSD$");
 
 #include "opt_inet.h"
 #include "opt_inet6.h"
-#include "opt_carp.h"
 
 #include <sys/param.h>
 #include <sys/mbuf.h>
@@ -121,10 +120,8 @@ __FBSDID("$FreeBSD$");
 #include <netinet6/ip6_var.h>
 #endif
 #if defined(INET) || defined(INET6)
-#ifdef DEV_CARP
 #include <netinet/ip_carp.h>
 #endif
-#endif
 #include <machine/in_cksum.h>
 #include <netinet/if_ether.h> /* for struct arpcom */
 #include <net/bridgestp.h>
@@ -2144,6 +2141,10 @@ drop:
 	m_freem(m);
 }
 
+#if defined(INET) || defined(INET6)
+int (*carp_forus_p)(struct carp_if *, u_char *);
+#endif
+
 /*
  * bridge_input:
  *
@@ -2252,13 +2253,13 @@ bridge_input(struct ifnet *ifp, struct mbuf *m)
 		return (m);
 	}
 
-#if (defined(INET) || defined(INET6)) && defined(DEV_CARP)
+#if (defined(INET) || defined(INET6))
 #   define OR_CARP_CHECK_WE_ARE_DST(iface) \
 	|| ((iface)->if_carp \
-	    && carp_forus((iface)->if_carp, eh->ether_dhost))
+	    && (*carp_forus_p)((iface)->if_carp, eh->ether_dhost))
 #   define OR_CARP_CHECK_WE_ARE_SRC(iface) \
 	|| ((iface)->if_carp \
-	    && carp_forus((iface)->if_carp, eh->ether_shost))
+	    && (*carp_forus_p)((iface)->if_carp, eh->ether_shost))
 #else
 #   define OR_CARP_CHECK_WE_ARE_DST(iface)
 #   define OR_CARP_CHECK_WE_ARE_SRC(iface)
diff --git a/sys/net/if_ethersubr.c b/sys/net/if_ethersubr.c
index bbf9753..984d0bb 100644
--- a/sys/net/if_ethersubr.c
+++ b/sys/net/if_ethersubr.c
@@ -35,7 +35,6 @@
 #include "opt_inet6.h"
 #include "opt_ipx.h"
 #include "opt_netgraph.h"
-#include "opt_carp.h"
 #include "opt_mbuf_profiling.h"
 
 #include <sys/param.h>
@@ -70,6 +69,7 @@
 #include <netinet/in.h>
 #include <netinet/in_var.h>
 #include <netinet/if_ether.h>
+#include <netinet/ip_carp.h>
 #include <netinet/ip_var.h>
 #include <netinet/ip_fw.h>
 #include <netinet/ipfw/ip_fw_private.h>
@@ -78,12 +78,6 @@
 #include <netinet6/nd6.h>
 #endif
 
-#if defined(INET) || defined(INET6)
-#ifdef DEV_CARP
-#include <netinet/ip_carp.h>
-#endif
-#endif
-
 #ifdef IPX
 #include <netipx/ipx.h>
 #include <netipx/ipx_if.h>
@@ -120,6 +114,11 @@ void	(*ng_ether_attach_p)(struct ifnet *ifp);
 void	(*ng_ether_detach_p)(struct ifnet *ifp);
 
 void	(*vlan_input_p)(struct ifnet *, struct mbuf *);
+#if defined(INET) || defined(INET6)
+int (*carp_forus_p)(struct ifnet *, u_char *);
+int (*carp_output_p)(struct ifnet *, struct mbuf *, struct sockaddr *,
+    struct rtentry *);
+#endif
 
 /* if_bridge(4) support */
 struct mbuf *(*bridge_input_p)(struct ifnet *, struct mbuf *); 
@@ -399,12 +398,10 @@ ether_output(struct ifnet *ifp, struct mbuf *m,
 	}
 
 #if defined(INET) || defined(INET6)
-#ifdef DEV_CARP
 	if (ifp->if_carp &&
-	    (error = carp_output(ifp, m, dst, NULL)))
+	    (error = (*carp_output_p)(ifp, m, dst, NULL)))
 		goto bad;
 #endif
-#endif
 
 	/* Handle ng_ether(4) processing, if any */
 	if (IFP2AC(ifp)->ac_netgraph != NULL) {
@@ -724,7 +721,6 @@ ether_input(struct ifnet *ifp, struct mbuf *m)
 	}
 
 #if defined(INET) || defined(INET6)
-#ifdef DEV_CARP
 	/*
 	 * Clear M_PROMISC on frame so that carp(4) will see it when the
 	 * mbuf flows up to Layer 3.
@@ -735,11 +731,10 @@ ether_input(struct ifnet *ifp, struct mbuf *m)
 	 * TODO: Maintain a hash table of ethernet addresses other than
 	 * ether_dhost which may be active on this ifp.
 	 */
-	if (ifp->if_carp && carp_forus(ifp->if_carp, eh->ether_dhost)) {
+	if (ifp->if_carp && (*carp_forus_p)(ifp, eh->ether_dhost)) {
 		m->m_flags &= ~M_PROMISC;
 	} else
 #endif
-#endif
 	{
 		/*
 		 * If the frame received was not for our MAC address, set the