add address family to/from string helper functions.

Add the functions family_name and read_family to convert an address
family to a string and to convernt a string to an address family.
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

include/utils.h

@@ -109,6 +109,9 @@ extern const char *format_host(int af, int len, const void *addr,
 extern const char *rt_addr_n2a(int af, int len, const void *addr,
 			       char *buf, int buflen);
 
+extern int read_family(const char *name);
+extern const char *family_name(int family);
+
 void missarg(const char *) __attribute__((noreturn));
 void invarg(const char *, const char *) __attribute__((noreturn));
 void duparg(const char *, const char *) __attribute__((noreturn));

ip/ip.c

@@ -190,21 +190,11 @@ int main(int argc, char **argv)
 			argv++;
 			if (argc <= 1)
 				usage();
-			if (strcmp(argv[1], "inet") == 0)
-				preferred_family = AF_INET;
-			else if (strcmp(argv[1], "inet6") == 0)
-				preferred_family = AF_INET6;
-			else if (strcmp(argv[1], "dnet") == 0)
-				preferred_family = AF_DECnet;
-			else if (strcmp(argv[1], "link") == 0)
-				preferred_family = AF_PACKET;
-			else if (strcmp(argv[1], "ipx") == 0)
-				preferred_family = AF_IPX;
-			else if (strcmp(argv[1], "bridge") == 0)
-				preferred_family = AF_BRIDGE;
-			else if (strcmp(argv[1], "help") == 0)
+			if (strcmp(argv[1], "help") == 0)
 				usage();
 			else
+				preferred_family = read_family(argv[1]);
+			if (preferred_family == AF_UNSPEC)
 				invarg("invalid protocol family", argv[1]);
 		} else if (strcmp(opt, "-4") == 0) {
 			preferred_family = AF_INET;

lib/utils.c

@@ -666,6 +666,41 @@ const char *rt_addr_n2a(int af, int len, const void *addr, char *buf, int buflen
 	}
 }
 
+int read_family(const char *name)
+{
+	int family = AF_UNSPEC;
+	if (strcmp(name, "inet") == 0)
+		family = AF_INET;
+	else if (strcmp(name, "inet6") == 0)
+		family = AF_INET6;
+	else if (strcmp(name, "dnet") == 0)
+		family = AF_DECnet;
+	else if (strcmp(name, "link") == 0)
+		family = AF_PACKET;
+	else if (strcmp(name, "ipx") == 0)
+		family = AF_IPX;
+	else if (strcmp(name, "bridge") == 0)
+		family = AF_BRIDGE;
+	return family;
+}
+
+const char *family_name(int family)
+{
+	if (family == AF_INET)
+		return "inet";
+	if (family == AF_INET6)
+		return "inet6";
+	if (family == AF_DECnet)
+		return "dnet";
+	if (family == AF_PACKET)
+		return "link";
+	if (family == AF_IPX)
+		return "ipx";
+	if (family == AF_BRIDGE)
+		return "bridge";
+	return "???";
+}
+
 #ifdef RESOLVE_HOSTNAMES
 struct namerec
 {