On Sat, Oct 28, 2017 at 03:20:07PM +0800, Guan Junxiong wrote:

Think of some current advanced features of DM-Multipath combined with multipath-tools
such as path-latency priority grouping, intermittent IO error accounting for path
degradation, delayed or immediate or follow-over failback feature.
Those features, which is significant in some scenario, need to use per-controller block devices.
Therefore, I think it is worthy adding a CONFIG_NVME_MULTIPATHING knob to
hide or show per-controller block devices.

How about let me to add this this CONFIG_NVME_MULTIPATHING knob?

There is defintively not going to be a run-time nob, sorry.  You've
spent this work on dm-multipath after the nvme group pretty clearly
said that this is not what we are going to support, and we have not
interest in supporting this.  Especially as proper path discovery,
asymetic namespaces states and similar can only be supported properly
with the in-kernel code.