network: allow to configure routing policy rule even if requesting interface is not activated yet

In the kernel, all routing policy rules are not assigned to any interface,
and we can configure them even if the relevant interface is down state.

Fixes a regression caused by 4f8b153d90 (v257).
Fixes #36244.

src/network/networkd-link.c

@@ -200,6 +200,17 @@ bool link_is_ready_to_configure(Link *link, bool allow_unmanaged) {
         return check_ready_for_all_sr_iov_ports(link, allow_unmanaged, link_is_ready_to_configure_one);
 }
 
+bool link_is_ready_to_configure_by_name(Manager *manager, const char *name, bool allow_unmanaged) {
+        assert(manager);
+        assert(name);
+
+        Link *link;
+        if (link_get_by_name(manager, name, &link) < 0)
+                return false;
+
+        return link_is_ready_to_configure(link, allow_unmanaged);
+}
+
 void link_ntp_settings_clear(Link *link) {
         link->ntp = strv_free(link->ntp);
 }

src/network/networkd-link.h

@@ -225,6 +225,7 @@ typedef struct Link {
 typedef int (*link_netlink_message_handler_t)(sd_netlink*, sd_netlink_message*, Link*);
 
 bool link_is_ready_to_configure(Link *link, bool allow_unmanaged);
+bool link_is_ready_to_configure_by_name(Manager *manager, const char *name, bool allow_unmanaged);
 
 void link_ntp_settings_clear(Link *link);
 void link_dns_settings_clear(Link *link);

src/network/networkd-routing-policy-rule.c

@@ -872,6 +872,31 @@ int link_drop_routing_policy_rules(Link *link, bool only_static) {
         return r;
 }
 
+static int routing_policy_rule_is_ready_to_configure(const RoutingPolicyRule *rule, Link *link) {
+        assert(rule);
+        assert(link);
+        assert(link->manager);
+
+        /* For routing policy rules, it is not necessary to check operstate and friends of the interface.
+         * Hence, here we refuse to configure rules only when the interface is already removed, or in the
+         * failed state. */
+        if (!IN_SET(link->state, LINK_STATE_CONFIGURING, LINK_STATE_CONFIGURED))
+                return false;
+
+        /* Strictly speaking checking existence of IIF and OIF below is not necessary. But, configuring
+         * routing policy rule with non-existent IIF or OIF is mostly meaningless, and 'ip rule' command
+         * shows [detached] for such rules, that may confuse users. Let's postpone to configure if one of
+         * IIF/OIF does not exist. */
+
+        if (rule->iif && !link_is_ready_to_configure_by_name(link->manager, rule->iif, /* allow_unmanaged = */ true))
+                return false;
+
+        if (rule->oif && !link_is_ready_to_configure_by_name(link->manager, rule->oif, /* allow_unmanaged = */ true))
+                return false;
+
+        return true;
+}
+
 static int routing_policy_rule_process_request(Request *req, Link *link, RoutingPolicyRule *rule) {
         RoutingPolicyRule *existing;
         int r;
@@ -881,7 +906,7 @@ static int routing_policy_rule_process_request(Request *req, Link *link, Routing
         assert(link->manager);
         assert(rule);
 
-        if (!link_is_ready_to_configure(link, false))
+        if (!routing_policy_rule_is_ready_to_configure(rule, link))
                 return 0;
 
         r = routing_policy_rule_configure(rule, link, req);