systemctl: allow disable on the unit file path, but warn about it (#3806)

systemd now returns an error when it is asked to perform disable on the
unit file path. In the past this was allowed, but systemd never really
considered an actual content of the [Install] section of the unit
file. Instead it performed disable on the unit name, i.e. purged all
symlinks pointing to the given unit file (undo of implicit link action
done by systemd when enable is called on the unit file path) and all
symlinks that have the same basename as the given unit file.

However, to notice that [Install] info of the file is not consulted one
must create additional symlinks manually. I argue that in most cases
users do not create such links. Let's be nice to our users and don't
break existing scripts that expect disable to work with the unit file
path.

Fixes #3706.

src/systemctl/systemctl.c

@@ -5670,6 +5670,29 @@ static int mangle_names(char **original_names, char ***mangled_names) {
         return 0;
 }
 
+static int normalize_names(char **names, bool warn_if_path) {
+        char **u;
+        bool was_path = false;
+
+        STRV_FOREACH(u, names) {
+                int r;
+
+                if (!is_path(*u))
+                        continue;
+
+                r = free_and_strdup(u, basename(*u));
+                if (r < 0)
+                        return log_error_errno(r, "Failed to normalize unit file path: %m");
+
+                was_path = true;
+        }
+
+        if (warn_if_path && was_path)
+                log_warning("Warning: Can't execute disable on the unit file path. Proceeding with the unit name.");
+
+        return 0;
+}
+
 static int unit_exists(const char *unit) {
         _cleanup_(sd_bus_message_unrefp) sd_bus_message *reply = NULL;
         _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
@@ -5737,6 +5760,12 @@ static int enable_unit(int argc, char *argv[], void *userdata) {
                 return daemon_reload(argc, argv, userdata);
         }
 
+        if (streq(verb, "disable")) {
+                r = normalize_names(names, true);
+                if (r < 0)
+                        return r;
+        }
+
         if (install_client_side()) {
                 if (streq(verb, "enable")) {
                         r = unit_file_enable(arg_scope, arg_runtime, arg_root, names, arg_force, &changes, &n_changes);