sd-netlink: don't treat NULL as root type-system

Explicitly export the root type-system to the type-system callers. This
avoids treating NULL as root, which for one really looks backwards (NULL
is usually a leaf, not root), and secondly prevents us from properly
debugging calling into non-nested types.

Also rename the root to "type_system_root". Once we support more than
rtnl, well will have to revisit that, anyway.

src/libsystemd/sd-netlink/netlink-message.c

@@ -68,7 +68,7 @@ int message_new(sd_netlink *rtnl, sd_netlink_message **ret, uint16_t type) {
         size_t size;
         int r;
 
-        r = type_system_get_type(NULL, &nl_type, type);
+        r = type_system_get_type(&type_system_root, &nl_type, type);
         if (r < 0)
                 return r;
 
@@ -874,7 +874,7 @@ int sd_netlink_message_rewind(sd_netlink_message *m) {
 
         assert(m->hdr);
 
-        r = type_system_get_type(NULL, &nl_type, m->hdr->nlmsg_type);
+        r = type_system_get_type(&type_system_root, &nl_type, m->hdr->nlmsg_type);
         if (r < 0)
                 return r;
 

src/libsystemd/sd-netlink/netlink-socket.c

@@ -243,7 +243,7 @@ int socket_read_message(sd_netlink *rtnl) {
                 }
 
                 /* check that we support this message type */
-                r = type_system_get_type(NULL, &nl_type, new_msg->nlmsg_type);
+                r = type_system_get_type(&type_system_root, &nl_type, new_msg->nlmsg_type);
                 if (r < 0) {
                         if (r == -EOPNOTSUPP)
                                 log_debug("sd-netlink: ignored message with unknown type: %i",

src/libsystemd/sd-netlink/netlink-types.c

@@ -476,7 +476,7 @@ static const NLType rtnl_types[RTM_MAX + 1] = {
         [RTM_GETNEIGH] = { .type = NETLINK_TYPE_NESTED, .type_system = &rtnl_neigh_type_system, .size = sizeof(struct ndmsg) },
 };
 
-const NLTypeSystem rtnl_type_system = {
+const NLTypeSystem type_system_root = {
         .count = ELEMENTSOF(rtnl_types),
         .types = rtnl_types,
 };
@@ -518,10 +518,7 @@ int type_system_get_type(const NLTypeSystem *type_system, const NLType **ret, ui
         const NLType *nl_type;
 
         assert(ret);
-
-        if (!type_system)
-                type_system = &rtnl_type_system;
-
+        assert(type_system);
         assert(type_system->types);
 
         if (type >= type_system->count)

src/libsystemd/sd-netlink/netlink-types.h

@@ -52,6 +52,8 @@ struct NLTypeSystemUnion {
         const NLTypeSystem *type_systems;
 };
 
+extern const NLTypeSystem type_system_root;
+
 uint16_t type_get_type(const NLType *type);
 size_t type_get_size(const NLType *type);
 void type_get_type_system(const NLType *type, const NLTypeSystem **ret);