How to add a block into blkio.throttle.io_service*?

[Julio Faracco]

Hi everybody,

I'm having some problems to understand how to add a block device into
blkio.throttle.* . Being more specific, I cannot see my block listed
into blkio.throttle.io_serviced.

An example... I'm running docker with a loopback device attached:
$ docker run -ti --device=/dev/loop16:/dev/loop16 fedora:latest bash

I can see it listed and included:
$ cat /sys/fs/cgroup/blkio/docker/2db640bc7bb28a3b6bf83dd7b7c0f146b4433e3ed5dfa6899f8498f9a19c52c5/blkio.throttle.io_serviced
7:16 Read 34
7:16 Write 0
7:16 Sync 34
7:16 Async 0
7:16 Discard 0
7:16 Total 34
8:0 Read 417
8:0 Write 0
8:0 Sync 417
8:0 Async 0
8:0 Discard 0
8:0 Total 417
Total 451

But how can I add it properly into my cgroup path?
I know that you need to enable block into that cgroup. But it is not
working for me. It works if I reset blkio.throttle.write_bps_device
and other fields:
# echo 0 > /sys/fs/cgroup/blkio/mypath/blkio.throttle.write_bps_device

I don't know if it is right. Does anyone know how to do it properly?

Thanks!

--
Julio Cesar Faracco