The ./contrib/docker-device-tool contains a tool to manipulate devicemapper thin-pool.
$ make shell ## inside build container $ go build contrib/docker-device-tool/device_tool.go # if devicemapper version is old and compilation fails, compile with `libdm_no_deferred_remove` tag $ go build -tags libdm_no_deferred_remove contrib/docker-device-tool/device_tool.go