vmspawn: only open runtime bus when needed for registration or scope allocation

The runtime bus (user bus in user scope, system bus in system scope) is
only needed for scope allocation (!arg_keep_unit) or machine registration
(arg_register != 0). When both are disabled the bus was still opened
unconditionally which causes unnecessary failures if the user bus is
unavailable.

Gate the runtime bus opening on the same condition nspawn already uses.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

diff --git a/src/vmspawn/vmspawn.c b/src/vmspawn/vmspawn.c
index c6289830fb707015cafe3478b98b8996ab8c362c..9610199c029300332e1f49fd9d2c3d26c58979a1 100644 (file)
--- a/src/vmspawn/vmspawn.c
+++ b/src/vmspawn/vmspawn.c
@@ -2246,21 +2246,23 @@ static int run_virtual_machine(int kvm_device_fd, int vhost_device_fd) {
                 (void) sd_bus_set_allow_interactive_authorization(system_bus, arg_ask_password);
         }
 
-        /* Scope allocation happens on the user bus if we are unpriv, otherwise system bus. */
+        /* Scope allocation and machine registration happen on the user bus if we are unpriv, otherwise system bus. */
         _cleanup_(sd_bus_flush_close_unrefp) sd_bus *user_bus = NULL;
         _cleanup_(sd_bus_unrefp) sd_bus *runtime_bus = NULL;
-        if (arg_runtime_scope == RUNTIME_SCOPE_SYSTEM)
-                runtime_bus = sd_bus_ref(system_bus);
-        else {
-                r = sd_bus_default_user(&user_bus);
-                if (r < 0)
-                        return log_error_errno(r, "Failed to open user bus: %m");
+        if (arg_register != 0 || !arg_keep_unit) {
+                if (arg_runtime_scope == RUNTIME_SCOPE_SYSTEM)
+                        runtime_bus = sd_bus_ref(system_bus);
+                else {
+                        r = sd_bus_default_user(&user_bus);
+                        if (r < 0)
+                                return log_error_errno(r, "Failed to open user bus: %m");
 
-                r = sd_bus_set_close_on_exit(user_bus, false);
-                if (r < 0)
-                        return log_error_errno(r, "Failed to disable close-on-exit behaviour: %m");
+                        r = sd_bus_set_close_on_exit(user_bus, false);
+                        if (r < 0)
+                                return log_error_errno(r, "Failed to disable close-on-exit behaviour: %m");
 
-                runtime_bus = sd_bus_ref(user_bus);
+                        runtime_bus = sd_bus_ref(user_bus);
+                }
         }
 
         bool use_kvm = arg_kvm > 0;