update ipifc with better ip6 error messages.

Reference: /n/atom/patch/applied/ipifcip6upd
Date: Fri Mar  7 16:07:56 CET 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/9/ip/ipifc.c	Fri Mar  7 16:07:36 2014
+++ /sys/src/9/ip/ipifc.c	Fri Mar  7 16:07:37 2014
@@ -16,6 +16,7 @@
 	NHASH		= 1<<6,
 	NCACHE		= 256,
 	QMAX		= 192*1024-1,
+	Maxv6repr	= (128/(4*4))*(4+1), /* limit of xxxx:xxxx:⋯ notation */
 };
 
 Medium *media[Maxmedia] = { 0 };
@@ -1152,7 +1153,7 @@
 {
 	if(isv4(addr) || ipcmp(addr, IPnoaddr) == 0)
 		return unknownv6;
-	if(islinklocal(addr) ||
+	else if(islinklocal(addr) ||
 	    isv6mcast(addr) && (addr[1] & 0xF) <= Link_local_scop)
 		return linklocalv6;
 	else
@@ -1607,7 +1608,7 @@
 {
 	int plen = 64;
 	long origint = NOW / 1000, preflt = ~0L, validlt = ~0L;
-	char addr[40], preflen[6];
+	char addr[Maxv6repr], preflen[6];
 	char *params[3];
 	uchar autoflag = 1, onlink = 1;
 	uchar prefix[IPaddrlen];
@@ -1635,9 +1636,17 @@
 		return Ebadarg;
 	}
 
-	if (parseip(prefix, argv[1]) != 6 || validlt < preflt || plen < 0 ||
-	    plen > 64 || islinklocal(prefix))
-		return Ebadarg;
+	if (parseip(prefix, argv[1]) != 6)
+		return "bad ipv6 address";
+	if (validlt < preflt)
+		return "valid ipv6 lifetime less than preferred lifetime";
+	if (plen < 0)
+		return "negative ipv6 prefix length";
+	/* i think that this length limit is bogus - geoff */
+//	if (plen > 64)
+//		return "ipv6 prefix length greater than 64;
+	if (islinklocal(prefix))
+		return "ipv6 prefix is link-local";
 
 	lifc = smalloc(sizeof(Iplifc));
 	lifc->onlink = (onlink != 0);
@@ -1648,10 +1657,10 @@
 
 	/* issue "add" ctl msg for v6 link-local addr and prefix len */
 	if(!ifc->m->pref2addr)
-		return Ebadarg;
+		return "no pref2addr on interface";
 	ifc->m->pref2addr(prefix, ifc->mac);	/* mac → v6 link-local addr */
-	sprint(addr, "%I", prefix);
-	sprint(preflen, "/%d", plen);
+	snprint(addr, sizeof addr, "%I", prefix);
+	snprint(preflen, sizeof preflen, "/%d", plen);
 	params[0] = "add";
 	params[1] = addr;
 	params[2] = preflen;
--- /sys/src/nix/ip/ipifc.c	Fri Mar  7 16:07:39 2014
+++ /sys/src/nix/ip/ipifc.c	Fri Mar  7 16:07:41 2014
@@ -16,6 +16,7 @@
 	NHASH		= 1<<6,
 	NCACHE		= 256,
 	QMAX		= 64*1024-1,
+	Maxv6repr	= (128/(4*4))*(4+1), /* limit of xxxx:xxxx:⋯ notation */
 };
 
 Medium *media[Maxmedia] = { 0 };
@@ -1152,7 +1153,7 @@
 {
 	if(isv4(addr) || ipcmp(addr, IPnoaddr) == 0)
 		return unknownv6;
-	if(islinklocal(addr) ||
+	else if(islinklocal(addr) ||
 	    isv6mcast(addr) && (addr[1] & 0xF) <= Link_local_scop)
 		return linklocalv6;
 	else
@@ -1607,7 +1608,7 @@
 {
 	int plen = 64;
 	long origint = NOW / 1000, preflt = ~0L, validlt = ~0L;
-	char addr[40], preflen[6];
+	char addr[Maxv6repr], preflen[6];
 	char *params[3];
 	uchar autoflag = 1, onlink = 1;
 	uchar prefix[IPaddrlen];
@@ -1635,9 +1636,17 @@
 		return Ebadarg;
 	}
 
-	if (parseip(prefix, argv[1]) != 6 || validlt < preflt || plen < 0 ||
-	    plen > 64 || islinklocal(prefix))
-		return Ebadarg;
+	if (parseip(prefix, argv[1]) != 6)
+		return "bad ipv6 address";
+	if (validlt < preflt)
+		return "valid ipv6 lifetime less than preferred lifetime";
+	if (plen < 0)
+		return "negative ipv6 prefix length";
+	/* i think that this length limit is bogus - geoff */
+//	if (plen > 64)
+//		return "ipv6 prefix length greater than 64;
+	if (islinklocal(prefix))
+		return "ipv6 prefix is link-local";
 
 	lifc = smalloc(sizeof(Iplifc));
 	lifc->onlink = (onlink != 0);
@@ -1648,10 +1657,10 @@
 
 	/* issue "add" ctl msg for v6 link-local addr and prefix len */
 	if(!ifc->m->pref2addr)
-		return Ebadarg;
+		return "no pref2addr on interface";
 	ifc->m->pref2addr(prefix, ifc->mac);	/* mac → v6 link-local addr */
-	sprint(addr, "%I", prefix);
-	sprint(preflen, "/%d", plen);
+	snprint(addr, sizeof addr, "%I", prefix);
+	snprint(preflen, sizeof preflen, "/%d", plen);
 	params[0] = "add";
 	params[1] = addr;
 	params[2] = preflen;