[PATCH 06/17] block: introduce GENHD_FL_HIDDEN

[Guan Junxiong]

Hi Christoph,

On 2017/10/28 14:38, Christoph Hellwig wrote:
> On Tue, Oct 24, 2017 at 05:40:00PM -0400, Mike Snitzer wrote:
>> Having the NVme driver go to such lengths to hide its resources from
>> upper layers is certainly the work of an evil genius experiencing some
>> serious territorial issues.  Not sugar-coating it.. you wouldn't.
> 
> I'm pretty surre Hannes will appreciate being called an evil genius :)
> 
>> I kept meaning to reply to your earlier iterations on this series to
>> ask: can we please get a CONFIG_NVME_MULTIPATHING knob to make it so
>> that the NVMe driver doesn't implicitly consume (and hide) all
>> per-controler devices?
> 
> I thought about adding it, but mostly for a different reason: it's
> quite a bit of code, and we now start to see NVMe in deeply embedded
> contexts, e.g. the latest Compact Flash spec is based on NVMe, so it
> might be a good idea to give people a chance to avoid the overhead.
> 

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?

Regards
Guan



>> Ah well.  There is only one correct way to do NVMe multipathing after
>> all right?
> 
> I don't think you'll get very useful results, even if you try.  But I
> guess we'll just have to tell people to use SuSE if they want NVMe
> multipathing to work then :)
> 
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