shared/install,systemctl,core: report offending file on installation error

Fixes #2191:

$ systemctl --root=/ enable sddm
Created symlink /etc/systemd/system/display-manager.service, pointing to /usr/lib/systemd/system/sddm.service.
$ sudo build/systemctl --root=/ enable gdm
Failed to enable unit, file /etc/systemd/system/display-manager.service already exists and is a symlink to /usr/lib/systemd/system/sddm.service.
$ sudo build/systemctl --root= enable sddm
$ sudo build/systemctl --root= enable gdm
Failed to enable unit: File /etc/systemd/system/display-manager.service already exists and is a symlink to /usr/lib/systemd/system/sddm.service.

(I tried a few different approaches to pass the error information back to the
caller. Adding a new parameter to hold the error results in a gigantic patch
and a lot of hassle to pass the args arounds. Adding this information to the
changes array is straightforward and can be more easily extended in the
future.)

In case local installation is performed, the full set of errors can be reported
and we do that. When running over dbus, only the first error is reported.

1 files changed, 9 insertions, 12 deletions

diff --git a/src/shared/bus-util.c b/src/shared/bus-util.c
index 677970b7f0..6a1877d8aa 100644
--- a/src/shared/bus-util.c
+++ b/src/shared/bus-util.c
@@ -2200,20 +2200,16 @@ int bus_deserialize_and_dump_unit_file_changes(sd_bus_message *m, bool quiet, Un
                 return bus_log_parse_error(r);
 
         while ((r = sd_bus_message_read(m, "(sss)", &type, &path, &source)) > 0) {
-                if (!quiet) {
-                        if (streq(type, "symlink"))
-                                log_info("Created symlink from %s to %s.", path, source);
-                        else if (streq(type, "unlink"))
-                                log_info("Removed symlink %s.", path);
-                        else if (streq(type, "masked"))
-                                log_info("Unit %s is masked, ignoring.", path);
-                        else
-                                log_notice("Manager reported unknown change type \"%s\" for %s.", type, path);
+                /* We expect only "success" changes to be sent over the bus.
+                   Hence, reject anything negative. */
+                UnitFileChangeType ch = unit_file_change_type_from_string(type);
+
+                if (ch < 0) {
+                        log_notice("Manager reported unknown change type \"%s\" for path \"%s\", ignoring.", type, path);
+                        continue;
                 }
 
-                r = unit_file_changes_add(changes, n_changes,
-                                          unit_file_change_type_from_string(type),
-                                          path, source);
+                r = unit_file_changes_add(changes, n_changes, ch, path, source);
                 if (r < 0)
                         return r;
         }
@@ -2224,6 +2220,7 @@ int bus_deserialize_and_dump_unit_file_changes(sd_bus_message *m, bool quiet, Un
         if (r < 0)
                 return bus_log_parse_error(r);
 
+        unit_file_dump_changes(0, NULL, *changes, *n_changes, false);
         return 0;
 }