[lxc-devel] [PATCH] hwaddr templating (with fixes from comments)

[lxc at zitta.fr]

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 at zitta.fr>
---
 doc/lxc.conf.sgml.in |  4 +++-
 src/lxc/confile.c    | 41 ++++++++++++++++++++++++++++++++++++++---
 src/lxc/utils.c      | 18 ++++++++++++++++++
 src/lxc/utils.h      |  2 ++
 4 files changed, 61 insertions(+), 4 deletions(-)

diff --git a/doc/lxc.conf.sgml.in b/doc/lxc.conf.sgml.in
index e6d9689..4bbeeeb 100644
--- a/doc/lxc.conf.sgml.in
+++ b/doc/lxc.conf.sgml.in
@@ -326,7 +326,9 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor,
Boston, MA 02110-1301 USA
           the interface mac address is dynamically allocated by
           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>
diff --git a/src/lxc/confile.c b/src/lxc/confile.c
index 0982b3e..c83c5bf 100644
--- a/src/lxc/confile.c
+++ b/src/lxc/confile.c
@@ -508,6 +508,28 @@ 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;
+
+    randinit();
+
+    while (*curs != '\0')
+    {
+        if ( *curs == 'x' || *curs == 'X' ) {
+            if (curs - hwaddr == 1) {
+                //ensure address is unicast
+                *curs = hex[(rand() & 0x0E)];
+            } else {
+                *curs = hex[rand() & 0x0F];
+            }
+        }
+        curs++;
+    }
+    return 0;
+}
+
 static int config_network_flags(const char *key, const char *value,
                 struct lxc_conf *lxc_conf)
 {
@@ -575,11 +597,24 @@ 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 *newval = strdup(value);
+
+    rand_complete_hwaddr(newval);
+
+    netdev = network_netdev(key, newval, &lxc_conf->network);
+    if (!netdev) {
+        free(newval);
         return -1;
+    };
 
-    return config_string_item(&netdev->hwaddr, value);
+    if (!newval || strlen(newval) == 0) {
+        free(newval);
+        netdev->hwaddr = NULL;
+        return 0;
+    }
+
+    netdev->hwaddr = newval;
+    return 0;
 }
 
 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 1f9ceea..0451a1d 100644
--- a/src/lxc/utils.c
+++ b/src/lxc/utils.c
@@ -1108,3 +1108,21 @@ 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;
+    f = fopen("/dev/urandom", "r");
+    if (f) {
+        unsigned int seed;
+        int ret = fread(&seed, sizeof(seed), 1, f);
+        if (ret != 1)
+            seed = time(NULL);
+        fclose(f);
+        srand(seed);
+    } else
+        srand(time(NULL));
+}
diff --git a/src/lxc/utils.h b/src/lxc/utils.h
index 847a613..9018889 100644
--- a/src/lxc/utils.h
+++ b/src/lxc/utils.h
@@ -265,5 +265,7 @@ 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 void randinit(void);
 
 #endif
-- 
1.8.3.2