[lxc-devel] hwaddr tuning in templates

[Guillaume ZITTA]

>> If not, my proposal:
>>  I set an incomplete (prefix) lxc.network.hwaddr in default conf.
>>  lxc-create complete it randomly and write it to the container's 
>> config.
>> 
>> Does it make sense?
> 
> I think so.  Just 'xx' in place of real numbers?
> 
>> I do not/can't code in C, but perhaps I should try  ...
>> 
>> Guillaume ZITTA

Please be kind, it's the second time I do "C" of my life :)

Note about randinit():
  that kind of util can be used in network.c/lxc_mkifname() and 
lxccontainer.c/new_hwaddr()

It works for me, I did 1000 destroy/create (with fake template) in 43 
sec without mac duplicate.

If I'm not completely doing wrong, I'll provide patch for manpage and 
HAVE_RAND_R ifdef.

please comment.

diff --git a/src/lxc/confile.c b/src/lxc/confile.c
index c5ec4f3..5721e05 100644
--- a/src/lxc/confile.c
+++ b/src/lxc/confile.c
@@ -509,6 +509,24 @@ static int macvlan_mode(int *valuep, const char 
*value)
  	return -1;
  }

+char *rand_complete_hwaddr(const char *hwaddr)
+{
+	const char hex[] = "0123456789abcdef";
+	char *retval=NULL;
+	retval = strdup(hwaddr);
+	char *curs = retval;
+
+	randinit();
+
+	while (*curs != '\0')
+	{
+		if ( *curs == 'x' || *curs == 'X' )
+			*curs = hex[rand() & 0x0F];
+		curs++;
+	}
+	return retval;
+}
+
  static int config_network_flags(const char *key, const char *value,
  				struct lxc_conf *lxc_conf)
  {
@@ -576,11 +594,13 @@ static int config_network_hwaddr(const char *key, 
const char *value,
  {
  	struct lxc_netdev *netdev;

-	netdev = network_netdev(key, value, &lxc_conf->network);
+	const char *newval = rand_complete_hwaddr(value);
+
+	netdev = network_netdev(key, newval, &lxc_conf->network);
  	if (!netdev)
  		return -1;

-	return config_string_item(&netdev->hwaddr, value);
+	return config_string_item(&netdev->hwaddr, newval);
  }

  static int config_network_vlan_id(const char *key, const char *value,
diff --git a/src/lxc/utils.c b/src/lxc/utils.c
index 785f3e6..204179e 100644
--- a/src/lxc/utils.c
+++ b/src/lxc/utils.c
@@ -1126,3 +1126,25 @@ void **lxc_append_null_to_array(void **array, 
size_t count)
  	}
  	return array;
  }
+
+void randinit(void)
+{
+	/*
+	srand pre-seed function based on /dev/urandom
+	*/
+	FILE *f;
+	process_lock();
+	f = fopen("/dev/urandom", "r");
+	process_unlock();
+	if (f) {
+		unsigned int seed;
+		int ret = fread(&seed, sizeof(seed), 1, f);
+		if (ret != 1)
+			seed = time(NULL);
+		process_lock();
+		fclose(f);
+		process_unlock();
+		srand(seed);
+	} else
+		srand(time(NULL));
+}
\ No newline at end of file
diff --git a/src/lxc/utils.h b/src/lxc/utils.h
index 945f1de..f20339b 100644
--- a/src/lxc/utils.h
+++ b/src/lxc/utils.h
@@ -270,4 +270,7 @@ extern void **lxc_dup_array(void **array, lxc_dup_fn 
element_dup_fn, lxc_free_fn
  extern void **lxc_append_null_to_array(void **array, size_t count);

  extern void dump_stacktrace(void);
+
+//initialize rand with urandom
+extern void randinit(void);
  #endif