unit: handle nicely of certain unit types are not supported on specific systems

Containers do not really support .device, .automount or .swap units;
Systems compiled without support for swap do not support .swap units;
Systems without kdbus do not support .busname units.

With this change attempts to start a unsupported unit types will result
in an immediate "unsupported" job result, which is a lot more
descriptive then before. Also, attempts to start device units in
containers will now immediately fail instead of causing jobs to be
enqueued that never go away.

1 files changed, 15 insertions, 6 deletions

diff --git a/src/core/manager.c b/src/core/manager.c
index 7653850cd4..afd911d899 100644
--- a/src/core/manager.c
+++ b/src/core/manager.c
@@ -946,20 +946,29 @@ Manager* manager_free(Manager *m) {
 }
 
 int manager_enumerate(Manager *m) {
-        int r = 0, q;
+        int r = 0;
         UnitType c;
 
         assert(m);
 
         /* Let's ask every type to load all units from disk/kernel
          * that it might know */
-        for (c = 0; c < _UNIT_TYPE_MAX; c++)
-                if (unit_vtable[c]->enumerate) {
-                        q = unit_vtable[c]->enumerate(m);
-                        if (q < 0)
-                                r = q;
+        for (c = 0; c < _UNIT_TYPE_MAX; c++) {
+                int q;
+
+                if (unit_vtable[c]->supported && !unit_vtable[c]->supported(m)) {
+                        log_info("Unit type .%s is not supported on this system.", unit_type_to_string(c));
+                        continue;
                 }
 
+                if (!unit_vtable[c]->enumerate)
+                        continue;
+
+                q = unit_vtable[c]->enumerate(m);
+                if (q < 0)
+                        r = q;
+        }
+
         manager_dispatch_load_queue(m);
         return r;
 }