sd-netlink: introduce rtnl_resolve_link_alternative_names()

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

@@ -593,6 +593,7 @@ static const NLType rtnl_link_types[] = {
         [IFLA_MIN_MTU]          = { .type = NETLINK_TYPE_U32 },
         [IFLA_MAX_MTU]          = { .type = NETLINK_TYPE_U32 },
         [IFLA_PROP_LIST]        = { .type = NETLINK_TYPE_NESTED, .type_system = &rtnl_prop_list_type_system },
+        [IFLA_ALT_IFNAME]       = { .type = NETLINK_TYPE_STRING, .size = ALTIFNAMSIZ - 1 },
 };
 
 static const NLTypeSystem rtnl_link_type_system = {

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

@@ -123,6 +123,35 @@ int rtnl_set_link_alternative_names(sd_netlink **rtnl, int ifindex, char * const
         return 0;
 }
 
+int rtnl_resolve_link_alternative_name(sd_netlink **rtnl, const char *name, int *ret) {
+        _cleanup_(sd_netlink_message_unrefp) sd_netlink_message *message = NULL, *reply = NULL;
+        int r;
+
+        assert(rtnl);
+        assert(name);
+        assert(ret);
+
+        if (!*rtnl) {
+                r = sd_netlink_open(rtnl);
+                if (r < 0)
+                        return r;
+        }
+
+        r = sd_rtnl_message_new_link(*rtnl, &message, RTM_GETLINK, 0);
+        if (r < 0)
+                return r;
+
+        r = sd_netlink_message_append_string(message, IFLA_ALT_IFNAME, name);
+        if (r < 0)
+                return r;
+
+        r = sd_netlink_call(*rtnl, message, 0, &reply);
+        if (r < 0)
+                return r;
+
+        return sd_rtnl_message_link_get_ifindex(reply, ret);
+}
+
 int rtnl_message_new_synthetic_error(sd_netlink *rtnl, int error, uint32_t serial, sd_netlink_message **ret) {
         struct nlmsgerr *err;
         int r;

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

@@ -50,6 +50,7 @@ static inline bool rtnl_message_type_is_qdisc(uint16_t type) {
 int rtnl_set_link_name(sd_netlink **rtnl, int ifindex, const char *name);
 int rtnl_set_link_properties(sd_netlink **rtnl, int ifindex, const char *alias, const struct ether_addr *mac, uint32_t mtu);
 int rtnl_set_link_alternative_names(sd_netlink **rtnl, int ifindex, char * const *alternative_names);
+int rtnl_resolve_link_alternative_name(sd_netlink **rtnl, const char *name, int *ret);
 
 int rtnl_log_parse_error(int r);
 int rtnl_log_create_error(int r);