[PATCHv4] nvme: allow to re-attach namespaces after all paths are down

[Hannes Reinecke]

On 5/17/21 8:20 PM, Sagi Grimberg wrote:
> 
>>> That is because we keep the device node around even though it doesn't
>>> have any bottom devices. Which is what I think Hannes tried to fix
>>> in an earlier patch.
>>>
>>> Also, if an NVM subsystem happens to recycle nsids, it will trigger
>>> pretty surely. So I'm not sure this is an obscure case...
>>
>> I'm not very concerned because (1) deleting an in-use namespace is
>> surely a user error, and (2) it currently doesn't work either, and no
>> one's complained yet AFAIK.
> 
> You're not wrong. It's just that one error (on ns X) can manifest in
> other potentially completely different namespaces created. I guess
> this kind of thing can happen when ns administration is done by
> adminX (or scriptX) and the ns mounting is done by userY where what each
> is doing is unknown to each other.

This can only happen if NSFEAT bit 3 is not set and the namespace does 
not provide a UUID.
So if we are concerned about that we can restrict nvme multipathing to 
exclude these scenarios.
But in all other cases CNS 03 _is_ identifying the namespace, and cannot 
be re-used for other namespaces.
And we are keeping a copy of CNS 03 in nshead, so we'll be safe there.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
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