[PATCH 06/17] block: introduce GENHD_FL_HIDDEN

[Guan Junxiong]

On 2017/10/28 15:42, Christoph Hellwig wrote:
> 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.
> 
Does it mean some extra works such as:
1) showing the path topology of nvme multipath device
2) daemon to implement immediate and delayed failback
3) detecting sub-healthy path due to shaky link
4) grouping paths besides ANA
...
and so on,
need to integrate into the user-space tool such as nvme-cli
or a new invented user-space tool named "nvme-mpath" ?
Which do you prefer?

And the kernel also needs to export more setting and getting methods.

Regards
Guan
.