This change introduce mac address templating.

By setting lxc.network.hwaddr to something like fe:xx:xx:xx:xx:xx each
"x" will be replaced by a random value.  If less significant bit of
first byte is "templated", it will be set to 0.

This change introduce also a common randinit() function that could be
used to initialize random generator.

Signed-off-by: gza <lxc@zitta.fr>
Acked-by: Serge Hallyn <serge.hallyn@ubuntu.com>

doc/lxc.conf.sgml.in

@@ -361,6 +361,9 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 	      default to the virtual interface, but in some cases,
 	      this is needed to resolve a mac address conflict or to
 	      always have the same link-local ipv6 address
+	      always have the same link-local ipv6 address.
+	      Any "x" in address will be replaced by random value,
+	      this allows setting hwaddr templates.
 	    </para>
 	  </listitem>
 	</varlistentry>

src/lxc/confile.c

@@ -510,6 +510,37 @@ static int macvlan_mode(int *valuep, const char *value)
 	return -1;
 }
 
+static int rand_complete_hwaddr(char *hwaddr)
+{
+	const char hex[] = "0123456789abcdef";
+	char *curs = hwaddr;
+
+#ifndef HAVE_RAND_R
+	randseed(true);
+#else
+	unsigned int seed=randseed(false);
+#endif
+	while (*curs != '\0')
+	{
+		if ( *curs == 'x' || *curs == 'X' ) {
+			if (curs - hwaddr == 1) {
+				//ensure address is unicast
+#ifdef HAVE_RAND_R
+				*curs = hex[rand_r(&seed) & 0x0E];
+			} else {
+				*curs = hex[rand_r(&seed) & 0x0F];
+#else
+				*curs = hex[rand() & 0x0E];
+			} else {
+				*curs = hex[rand() & 0x0F];
+#endif
+			}
+		}
+		curs++;
+	}
+	return 0;
+}
+
 static int config_network_flags(const char *key, const char *value,
 				struct lxc_conf *lxc_conf)
 {
@@ -577,11 +608,27 @@ static int config_network_hwaddr(const char *key, const char *value,
 {
 	struct lxc_netdev *netdev;
 
-	netdev = network_netdev(key, value, &lxc_conf->network);
-	if (!netdev)
+	char *new_value = strdup(value);
+	if (!new_value) {
+		SYSERROR("failed to strdup '%s': %m", value);
 		return -1;
+	}
+	rand_complete_hwaddr(new_value);
 
-	return config_string_item(&netdev->hwaddr, value);
+	netdev = network_netdev(key, new_value, &lxc_conf->network);
+	if (!netdev) {
+		free(new_value);
+		return -1;
+	};
+
+	if (!new_value || strlen(new_value) == 0) {
+		free(new_value);
+		netdev->hwaddr = NULL;
+		return 0;
+	}
+
+	netdev->hwaddr = new_value;
+	return 0;
 }
 
 static int config_network_vlan_id(const char *key, const char *value,

src/lxc/utils.c

@@ -1084,3 +1084,25 @@ void **lxc_append_null_to_array(void **array, size_t count)
 	}
 	return array;
 }
+
+int randseed(bool srand_it)
+{
+	/*
+	   srand pre-seed function based on /dev/urandom
+	   */
+	unsigned int seed=time(NULL)+getpid();
+
+	FILE *f;
+	f = fopen("/dev/urandom", "r");
+	if (f) {
+		int ret = fread(&seed, sizeof(seed), 1, f);
+		if (ret != 1)
+			DEBUG("unable to fread /dev/urandom, %s, fallback to time+pid rand seed", strerror(errno));
+		fclose(f);
+	}
+
+	if (srand_it)
+		srand(seed);
+
+	return seed;
+}

src/lxc/utils.h

@@ -257,5 +257,7 @@ extern void lxc_free_array(void **array, lxc_free_fn element_free_fn);
 extern size_t lxc_array_len(void **array);
 
 extern void **lxc_append_null_to_array(void **array, size_t count);
+//initialize rand with urandom
+extern int randseed(bool);
 
 #endif