Read cgroups data without mounting it
The only interface you get in the user space is by mounting cgroups or from the /proc/<pid>/cgourps, (but only limited to the cgroups a process belongs to). If you are looking for a syscall() for reading cgroups data, its not available IMU. Docker requires cgroups services (cgconfig, cgred, etc)to be running, therefore its would require you to mount the cgroups.