+ rename and document an unused field in struct arpcom (field is still

  there so there are no ABI changes);
+ replace 5 redefinitions of the IPF2AC macro with one in if_arp.h

Eventually (but before freezing the ABI) we need to get rid of
struct arpcom (initially with the help of some smart #defines
to avoid having to touch each and every driver, see below).

Apart from the struct ifnet, struct arpcom now only stores a copy
of the MAC address (ac_enaddr, but we already have another copy in
the struct ifnet -- if_addrhead), and a netgraph-specific field
which is _always_ accessed through the ifp, so it might well go
into the struct ifnet too (where, besides, there is already an entry
for AF_NETGRAPH data...)

Too bad ac_enaddr is widely referenced by all drivers. But
this can be fixed as follows:

#define ac_enaddr       ac_if.the_original_ac_enaddr_in_struct_ifnet

(note that the right hand side would likely be a pointer rather than
the base address of an array.)

5 files changed, 9 insertions, 4 deletions

diff --git a/sys/net/if_arp.h b/sys/net/if_arp.h
index 9afea76..6cc3ce9 100644
--- a/sys/net/if_arp.h
+++ b/sys/net/if_arp.h
@@ -100,6 +100,8 @@ struct arpreq {
  * Structure shared between the ethernet driver modules and
  * the address resolution code.  For example, each ec_softc or il_softc
  * begins with this structure.
+ * The code is written so that each *_softc _must_ begin with a
+ * struct arpcom, which in turn _must_ begin with a struct ifnet.
  */
 struct	arpcom {
 	/*
@@ -107,9 +109,11 @@ struct	arpcom {
 	 */
 	struct 	ifnet ac_if;		/* network-visible interface */
 	u_char	ac_enaddr[6];		/* ethernet hardware address */
-	int	ac_multicnt;		/* length of ac_multiaddrs list */
+	int	now_unused;	/* XXX was length of ac_multiaddrs list */
 	void	*ac_netgraph;		/* ng_ether(4) netgraph node info */
 };
+#define IFP2AC(ifp) ((struct arpcom *)(ifp))
+
 #endif
 
 #endif /* !_NET_IF_ARP_H_ */
diff --git a/sys/net/if_ethersubr.c b/sys/net/if_ethersubr.c
index 93791df..7bf473d 100644
--- a/sys/net/if_ethersubr.c
+++ b/sys/net/if_ethersubr.c
@@ -114,7 +114,6 @@ static	int ether_resolvemulti(struct ifnet *, struct sockaddr **,
 		struct sockaddr *);
 
 #define senderr(e) do { error = (e); goto bad;} while (0)
-#define IFP2AC(IFP) ((struct arpcom *)IFP)
 
 int
 ether_ipfw_chk(struct mbuf **m0, struct ifnet *dst,
diff --git a/sys/net/if_fddisubr.c b/sys/net/if_fddisubr.c
index 1003208..2e89840 100644
--- a/sys/net/if_fddisubr.c
+++ b/sys/net/if_fddisubr.c
@@ -98,7 +98,6 @@ static int fddi_output(struct ifnet *, struct mbuf *, struct sockaddr *,
 		       struct rtentry *); 
 static void fddi_input(struct ifnet *ifp, struct mbuf *m);
 
-#define	IFP2AC(IFP)	((struct arpcom *)IFP)
 #define	senderr(e)	do { error = (e); goto bad; } while (0)
 
 /*
diff --git a/sys/net/if_iso88025subr.c b/sys/net/if_iso88025subr.c
index 7062632..5f1b802 100644
--- a/sys/net/if_iso88025subr.c
+++ b/sys/net/if_iso88025subr.c
@@ -85,7 +85,6 @@ static const u_char iso88025_broadcastaddr[ISO88025_ADDR_LEN] =
 static int iso88025_resolvemulti (struct ifnet *, struct sockaddr **,
 				  struct sockaddr *);
 
-#define	IFP2AC(IFP)	((struct arpcom *)IFP)
 #define	senderr(e)	do { error = (e); goto bad; } while (0)
 
 /*
diff --git a/sys/net/if_var.h b/sys/net/if_var.h
index 9494129..989f8c5 100644
--- a/sys/net/if_var.h
+++ b/sys/net/if_var.h
@@ -187,6 +187,10 @@ struct ifnet {
 
 typedef void if_init_f_t(void *);
 
+/*
+ * XXX These aliases are terribly dangerous because they could apply
+ * to anything.
+ */
 #define	if_mtu		if_data.ifi_mtu
 #define	if_type		if_data.ifi_type
 #define if_physical	if_data.ifi_physical