[PATCH] nvme: allow to re-attach namespaces after all paths are down

[Hannes Reinecke]

On 5/11/21 11:37 PM, Keith Busch wrote:
> On Mon, May 10, 2021 at 03:25:04PM -0700, Sagi Grimberg wrote:
>> Hannes, you sent a patch like this before, my comment was that a nshead
>> should be removed before the final reference (which who knows when it
>> will ever arrive) as if a nsid were to be reused by the controller for
>> a different namespace then we'd reject it so I'm not sure how this helps?
> 
> Hm, you're considering something like if a user does namespace
> management commands to delete one that is in-use (mounted, raid, etc),
> then creates and attaches a new namespace that happens to be assigned
> the same NSID.
> 
> The new one may get different EUI/NGUID values, so this approach here
> would prevent the namespace from being usable without additional user
> intervention. I think we'd want the driver to allocate an entirely new
> head in that case if we could detect that's what happened. There is also
> a possibility that the controller recycles the same NGUID for the new
> namespace, and that could be confusing for the application holding the
> open reference on the old namespace.
> 
... and, of course, none of this would happen if we would _not_ keep the
old nshead around. I'm still not sure _why_ this is considered
important. After all, things work perfectly when the CMIC bit is not
set; even device hot-removal and re-insertion (one of our IHVs tested
the crap out of that one, and I can confidently state the nvme stack did
not cause any issue there. Unlike other subsystems ...).

So I'm really curious which use-case we're trying to support with that;
EIO is EIO, and the application couldn't care less if it's generated due
to the nshead running out of paths or the nshead not existing...

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		           Kernel Storage Architect
hare at suse.de			                  +49 911 74053 688
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