core: move initialization of -.slice and init.scope into the unit_load() callbacks

Previously, we'd synthesize the root slice unit and the init scope unit in the
enumerator callbacks for the unit type. This is problematic if either of them
is already referenced from a unit that is loaded as result of another unit
type's enumerator logic.

Let's clean this up and simply create the two objects from the enumerator
callbacks, if they are not around yet. Do the actual filling in of the settings
from the unit_load() callbacks, to match how other units are loaded.

Fixes: #4322

2 files changed, 60 insertions, 22 deletions

diff --git a/src/core/scope.c b/src/core/scope.c
index e7583f6d89..af0c43c7da 100644
--- a/src/core/scope.c
+++ b/src/core/scope.c
@@ -147,6 +147,34 @@ static int scope_verify(Scope *s) {
         return 0;
 }
 
+static int scope_load_init_scope(Unit *u) {
+        assert(u);
+
+        if (!unit_has_name(u, SPECIAL_INIT_SCOPE))
+                return 0;
+
+        u->transient = true;
+        u->no_gc = true;
+
+        /* init.scope is a bit special, as it has to stick around forever. Because of its special semantics we
+         * synthesize it here, instead of relying on the unit file on disk. */
+
+        u->default_dependencies = false;
+        u->ignore_on_isolate = true;
+        u->refuse_manual_start = true;
+        u->refuse_manual_stop = true;
+
+        SCOPE(u)->kill_context.kill_signal = SIGRTMIN+14;
+
+        /* Prettify things, if we can. */
+        if (!u->description)
+                u->description = strdup("System and Service Manager");
+        if (!u->documentation)
+                (void) strv_extend(&u->documentation, "man:systemd(1)");
+
+        return 1;
+}
+
 static int scope_load(Unit *u) {
         Scope *s = SCOPE(u);
         int r;
@@ -158,6 +186,9 @@ static int scope_load(Unit *u) {
                 /* Refuse to load non-transient scope units, but allow them while reloading. */
                 return -ENOENT;
 
+        r = scope_load_init_scope(u);
+        if (r < 0)
+                return r;
         r = unit_load_fragment_and_dropin_optional(u);
         if (r < 0)
                 return r;
@@ -543,25 +574,14 @@ static void scope_enumerate(Manager *m) {
                 r = unit_add_name(u, SPECIAL_INIT_SCOPE);
                 if (r < 0)  {
                         unit_free(u);
-                        log_error_errno(r, "Failed to add init.scope name");
+                        log_error_errno(r, "Failed to add the " SPECIAL_INIT_SCOPE " name: %m");
                         return;
                 }
         }
 
         u->transient = true;
-        u->default_dependencies = false;
         u->no_gc = true;
-        u->ignore_on_isolate = true;
-        u->refuse_manual_start = true;
-        u->refuse_manual_stop = true;
         SCOPE(u)->deserialized_state = SCOPE_RUNNING;
-        SCOPE(u)->kill_context.kill_signal = SIGRTMIN+14;
-
-        /* Prettify things, if we can. */
-        if (!u->description)
-                u->description = strdup("System and Service Manager");
-        if (!u->documentation)
-                (void) strv_extend(&u->documentation, "man:systemd(1)");
 
         unit_add_to_load_queue(u);
         unit_add_to_dbus_queue(u);
diff --git a/src/core/slice.c b/src/core/slice.c
index 03fe797f27..0fef29661f 100644
--- a/src/core/slice.c
+++ b/src/core/slice.c
@@ -130,6 +130,30 @@ static int slice_verify(Slice *s) {
         return 0;
 }
 
+static int slice_load_root_slice(Unit *u) {
+        assert(u);
+
+        if (!unit_has_name(u, SPECIAL_ROOT_SLICE))
+                return 0;
+
+        u->no_gc = true;
+
+        /* The root slice is a bit special. For example it is always running and cannot be terminated. Because of its
+         * special semantics we synthesize it here, instead of relying on the unit file on disk. */
+
+        u->default_dependencies = false;
+        u->ignore_on_isolate = true;
+        u->refuse_manual_start = true;
+        u->refuse_manual_stop = true;
+
+        if (!u->description)
+                u->description = strdup("Root Slice");
+        if (!u->documentation)
+                u->documentation = strv_new("man:systemd.special(7)", NULL);
+
+        return 1;
+}
+
 static int slice_load(Unit *u) {
         Slice *s = SLICE(u);
         int r;
@@ -137,6 +161,9 @@ static int slice_load(Unit *u) {
         assert(s);
         assert(u->load_state == UNIT_STUB);
 
+        r = slice_load_root_slice(u);
+        if (r < 0)
+                return r;
         r = unit_load_fragment_and_dropin_optional(u);
         if (r < 0)
                 return r;
@@ -283,23 +310,14 @@ static void slice_enumerate(Manager *m) {
                 r = unit_add_name(u, SPECIAL_ROOT_SLICE);
                 if (r < 0) {
                         unit_free(u);
-                        log_error_errno(r, "Failed to add -.slice name");
+                        log_error_errno(r, "Failed to add the "SPECIAL_ROOT_SLICE " name: %m");
                         return;
                 }
         }
 
-        u->default_dependencies = false;
         u->no_gc = true;
-        u->ignore_on_isolate = true;
-        u->refuse_manual_start = true;
-        u->refuse_manual_stop = true;
         SLICE(u)->deserialized_state = SLICE_ACTIVE;
 
-        if (!u->description)
-                u->description = strdup("Root Slice");
-        if (!u->documentation)
-                (void) strv_extend(&u->documentation, "man:systemd.special(7)");
-
         unit_add_to_load_queue(u);
         unit_add_to_dbus_queue(u);
 }