[dm-devel] missing device-mapper functionality

["goggin, edward" <egoggin emc com>]

The inability to monitor block I/O statistics via iostat for device-mapper
mapped devices seems like a big loss.  Are there plans to provide this
feature?

Seems like being able to initiate i/o requests to device-mapper target
devices from within a device-mapper target driver is a missing link in
the device-mapper architecture.  Are there plans to provide this feature?

Since the multipath hardware context code for the CLARiion places
path priority group initialization I/O requests directly on its target
device queues it must be the case the CLARiion target devices must
be ones which have a request_fn_proc() queue service function -- which
rules out using other device-mapper mapped devices or md devices as
target devices.  This restriction appears not to be in place for other
storage systems supported by multipath.