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

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Message-ID: <20181116091458.GA17267@lst.de>
Date:   Fri, 16 Nov 2018 10:14:58 +0100
From:   Christoph Hellwig <hch@....de>
To:     Mike Snitzer <snitzer@...hat.com>
Cc:     linux-nvme@...ts.infradead.org, Hannes Reinecke <hare@...e.de>,
        Keith Busch <keith.busch@...el.com>,
        Sagi Grimberg <sagi@...mberg.me>, hch@....de, axboe@...nel.dk,
        Martin Wilck <mwilck@...e.com>, lijie <lijie34@...wei.com>,
        xose.vazquez@...il.com, chengjike.cheng@...wei.com,
        shenhong09@...wei.com, dm-devel@...hat.com,
        wangzhoumengjian@...wei.com, christophe.varoqui@...nsvc.com,
        bmarzins@...hat.com, sschremm@...app.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nvme: allow ANA support to be independent of native
 multipathing

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.

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.