better handling of interface name parameter

dhtest.c

@@ -41,7 +41,7 @@ u_char dhmac[ETHER_ADDR_LEN] = { 0 };
 u_char dmac[ETHER_ADDR_LEN];
 
 char dhmac_fname[20];
-char iface_name[30] = { 0 };
+char *iface_name = "eth0";
 char ip_str[128];
 u_int8_t dhmac_flag = 0;
 u_int32_t server_id = { 0 }, option50_ip = { 0 };
@@ -187,12 +187,7 @@ int main(int argc, char *argv[])
 				break;
 
 			case 'i':
-				iface = if_nametoindex(optarg);
-				if(iface == 0) {
-					fprintf(stdout, "Interface doesnot exist\n");
-					exit(2);
-				}
-				strncpy(iface_name, optarg, 29);
+				iface_name = optarg;
 				break;
 
 			case 'v':
@@ -341,6 +336,11 @@ int main(int argc, char *argv[])
 		print_help(argv[0]);
 		exit(2);
 	}
+	iface = if_nametoindex(iface_name);
+	if(iface == 0) {
+		fprintf(stdout, "Interface %s does not exist\n", iface_name);
+		exit(2);
+	}
 	/* Opens the PF_PACKET socket */
 	if(open_socket() < 0) {
 		if (nagios_flag)

functions.c

@@ -68,9 +68,6 @@ int set_promisc()
 {
 	int status;
 	struct ifreq ifr;
-	if(!strlen(iface_name)) {
-		strcpy(iface_name, "eth0");
-	}
 	strcpy(ifr.ifr_name, iface_name);
 	ifr.ifr_flags = (IFF_PROMISC | IFF_UP);
 	status = ioctl(sock_packet, SIOCSIFFLAGS, &ifr);
@@ -109,9 +106,6 @@ u_int32_t get_interface_address()
 	int status;
 	struct ifreq ifr;
 
-	if(!strlen(iface_name)) {
-		strcpy(iface_name, "eth0");
-	}
 	strcpy(ifr.ifr_name, iface_name);
 	ifr.ifr_addr.sa_family = AF_INET;
 	status = ioctl(sock_packet, SIOCGIFADDR, &ifr);

headers.h

@@ -351,7 +351,7 @@ extern u_char dhmac[ETHER_ADDR_LEN];
 extern u_char dmac[ETHER_ADDR_LEN];
 
 extern char dhmac_fname[20];
-extern char iface_name[30];
+extern char *iface_name;
 extern char ip_str[128];
 extern u_int32_t server_id, option50_ip;
 extern u_int8_t dhcp_release_flag;