[PATCH] nvme-core: update NS Attr Changed AEN handling for ANA group

[hch at lst.de]

On Thu, Dec 10, 2020 at 02:39:36AM +0900, Keith Busch wrote:
> > The use-case I'm trying to describe is that the admin on the storage array
> > is creating a namespace and attaching it to an existing subsystem,
> > completely without interaction from the host. It just so happens that this
> > new namespace has a different ANA group than the existing namespaces in this
> > subsystem.
> > Then the array has to notify the host about this.
> > And the whole discussion is about which AENs this controller/storage array
> > should be sending.
> 
> Fred keeps saying the spec's rules for NVMe's namespace create command
> from section 5.20 allow him to not send events, but it turns out you're
> not even using this command? Why would the spec's defined behavior apply
> to this proprietary use case?

I think we are in an even deeper mess here than I though.

 - one issue is the fact that the exception gets creating vs attaching
   and deleting vs detaching wrong, and that probably is my fault.
 - the other one is the wording should be shall not send the event
   when the creation is ONLY due to the creation of a namespace, that
   is not when a new ANA group shows up (and the way how ANA groups
   are created is out of scope)

So if we do a textual interpretation of the spec, the controller does
not only need to send the ANA AEN for the case we are debatting here,
but also for the case I specifically wanted to exclude.  Sigh.