tree-wide: prefer sending pifds over pids when creating scope units

src/nspawn/nspawn-register.c

@@ -194,7 +194,6 @@ int register_machine(
 
                 r = sd_bus_call(bus, m, 0, &error, NULL);
         }
-
         if (r < 0)
                 return log_error_errno(r, "Failed to register machine: %s", bus_error_message(&error, r));
 
@@ -226,7 +225,8 @@ int allocate_scope(
                 unsigned n_mounts,
                 int kill_signal,
                 char **properties,
-                sd_bus_message *properties_message) {
+                sd_bus_message *properties_message,
+                bool allow_pidfd) {
 
         _cleanup_(sd_bus_message_unrefp) sd_bus_message *m = NULL, *reply = NULL;
         _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
@@ -260,8 +260,19 @@ int allocate_scope(
 
         description = strjoina("Container ", machine_name);
 
-        r = sd_bus_message_append(m, "(sv)(sv)(sv)(sv)(sv)(sv)",
-                                  "PIDs", "au", 1, pid,
+        if (allow_pidfd) {
+                _cleanup_(pidref_done) PidRef pidref = PIDREF_NULL;
+                r = pidref_set_pid(&pidref, pid);
+                if (r < 0)
+                        return log_error_errno(r, "Failed to allocate PID reference: %m");
+
+                r = bus_append_scope_pidref(m, &pidref);
+        } else
+                r = sd_bus_message_append(m, "(sv)", "PIDs", "au", 1, pid);
+        if (r < 0)
+                return bus_log_create_error(r);
+
+        r = sd_bus_message_append(m, "(sv)(sv)(sv)(sv)(sv)",
                                   "Description", "s", description,
                                   "Delegate", "b", 1,
                                   "CollectMode", "s", "inactive-or-failed",
@@ -305,8 +316,15 @@ int allocate_scope(
                 return bus_log_create_error(r);
 
         r = sd_bus_call(bus, m, 0, &error, &reply);
-        if (r < 0)
+        if (r < 0) {
+                /* If this failed with a property we couldn't write, this is quite likely because the server
+                 * doesn't support PIDFDs yet, let's try without. */
+                if (allow_pidfd &&
+                    sd_bus_error_has_names(&error, SD_BUS_ERROR_UNKNOWN_PROPERTY, SD_BUS_ERROR_PROPERTY_READ_ONLY))
+                        return allocate_scope(bus, machine_name, pid, slice, mounts, n_mounts, kill_signal, properties, properties_message, /* allow_pidfd= */ false);
+
                 return log_error_errno(r, "Failed to allocate scope: %s", bus_error_message(&error, r));
+        }
 
         r = sd_bus_message_read(reply, "o", &object);
         if (r < 0)

src/nspawn/nspawn-register.h

@@ -10,5 +10,5 @@
 int register_machine(sd_bus *bus, const char *machine_name, pid_t pid, const char *directory, sd_id128_t uuid, int local_ifindex, const char *slice, CustomMount *mounts, unsigned n_mounts, int kill_signal, char **properties, sd_bus_message *properties_message, bool keep_unit, const char *service);
 int unregister_machine(sd_bus *bus, const char *machine_name);
 
-int allocate_scope(sd_bus *bus, const char *machine_name, pid_t pid, const char *slice, CustomMount *mounts, unsigned n_mounts, int kill_signal, char **properties, sd_bus_message *properties_message);
+int allocate_scope(sd_bus *bus, const char *machine_name, pid_t pid, const char *slice, CustomMount *mounts, unsigned n_mounts, int kill_signal, char **properties, sd_bus_message *properties_message, bool allow_pidfds);
 int terminate_scope(sd_bus *bus, const char *machine_name);

src/nspawn/nspawn.c

@@ -5074,7 +5074,8 @@ static int run_container(
                                 arg_custom_mounts, arg_n_custom_mounts,
                                 arg_kill_signal,
                                 arg_property,
-                                arg_property_message);
+                                arg_property_message,
+                                /* allow_pidfds= */ true);
                 if (r < 0)
                         return r;