cgtop: use common function to query cgroup root

show_cgroup_get_root_and_warn is renamed to show_cgroup_get_path_and_warn
because it now optionally allows querying a non-root path.

This removes duplicated code and teaches cgtop to combine
-M with a root prefix:

$ systemd-cgtop -M myprecious /system.slice
...

1 files changed, 2 insertions, 2 deletions

diff --git a/src/cgls/cgls.c b/src/cgls/cgls.c
index e6ec9640a8..1d21c1c20c 100644
--- a/src/cgls/cgls.c
+++ b/src/cgls/cgls.c
@@ -154,7 +154,7 @@ int main(int argc, char *argv[]) {
                 _cleanup_free_ char *root = NULL;
                 int i;
 
-                r = show_cgroup_get_root_and_warn(arg_machine, &root);
+                r = show_cgroup_get_path_and_warn(arg_machine, NULL, &root);
                 if (r < 0)
                         goto finish;
 
@@ -223,7 +223,7 @@ int main(int argc, char *argv[]) {
                 if (!done) {
                         _cleanup_free_ char *root = NULL;
 
-                        r = show_cgroup_get_root_and_warn(arg_machine, &root);
+                        r = show_cgroup_get_path_and_warn(arg_machine, NULL, &root);
                         if (r < 0)
                                 goto finish;