cgroup: add support for reserved cgroup 'root', for RT tasks

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/cgroup.c

@@ -156,6 +156,9 @@ int cgroup_service(char *name, int pid, struct cgroup *cg)
 	if (cg && cg->name[0]) {
 		char path[256];
 
+		if (!strcmp(cg->name, "root"))
+			return fnwrite(str("%d", pid), FINIT_CGPATH "/cgroup.procs");
+
 		snprintf(path, sizeof(path), "/sys/fs/cgroup/%s", cg->name);
 		if (fisdir(path))
 			group = cg->name;