Re: [PATCH] nvme: allow ANA support to be independent of native multipathing

[Hannes Reinecke]

On 11/16/18 10:14 AM, Christoph Hellwig wrote:
> On Thu, Nov 15, 2018 at 12:46:05PM -0500, Mike Snitzer wrote:
> > Whether or not ANA is present is a choice of the target implementation;
> > the host (and whether it supports multipathing) has _zero_ influence on
> > this.  If the target declares a path as 'inaccessible' the path _is_
> > inaccessible to the host.  As such, ANA support should be functional
> > even if native multipathing is not.
> >
> > Introduce ability to always re-read ANA log page as required due to ANA
> > error and make current ANA state available via sysfs -- even if native
> > multipathing is disabled on the host (e.g. nvme_core.multipath=N).
>
> The first part I could see, but I still want to make it conditional
> in some way as nvme is going into deeply embedded setups, and I don't
> want to carry the weight of the ANA code around for everyone.
Can you clarify this a bit?
We _do_ have the NVME multipath config option to deconfigure the whole 
thing during compile time; that isn't influenced with this patch.
So are you worried about the size of the ANA implementation itself?
Or are you worried about the size of the ANA structures?

> The second I fundamentally disagree with.  And even if you found agreement
> it would have to be in a separate patch as it is a separate feature.
Why? Where's the problem with re-reading the ANA log pages if we get an 
event indicating that we should?

Cheers,

Hannes
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Dr. Hannes Reinecke		   Teamlead Storage & Networking
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