generator: exit early when asked to generate fsck unit for / and /usr in initrd

Let's exit early if we are invoked to generate an fsck unit for the
rootfs or /usr of the initrd itself. The "systemd-root-fsck.service" and
"systemd-usr-fsck.service" units are after all for the host file
systems, and the initrd file hierarchy is from an unpacked cpio anyway.
Hence, this semantically doesn't really make sense, so quickly exit if
we detect this case. This allows us to remove some checks further down
the codepath.

src/shared/generator.c

@@ -138,6 +138,13 @@ int generator_write_fsck_deps(
         assert(what);
         assert(where);
 
+        /* Let's do an early exit if we are invoked for the root and /usr/ trees in the initrd, to avoid
+         * generating confusing log messages */
+        if (in_initrd() && PATH_IN_SET(where, "/", "/usr")) {
+                log_debug("Skipping fsck for %s in initrd.", where);
+                return 0;
+        }
+
         if (!is_device_path(what)) {
                 log_warning("Checking was requested for \"%s\", but it is not a device.", what);
                 return 0;
@@ -180,7 +187,7 @@ int generator_write_fsck_deps(
                          * Requires= from /usr onto a fsck@.service unit and that unit is shut down, then
                          * we'd have to unmount /usr too.  */
 
-                        dep = !in_initrd() && path_equal(where, "/usr") ? "Wants" : "Requires";
+                        dep = path_equal(where, "/usr") ? "Wants" : "Requires";
 
                         r = unit_name_from_path_instance("systemd-fsck", what, ".service", &_fsck);
                         if (r < 0)