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

[hch at lst.de]

On Wed, Dec 09, 2020 at 01:34:37PM -0800, Keith Busch wrote:
> Linux hosts currently want an ANA AEN anytime the host needs to refresh
> the ANA log. That includes any condition that adds groups that didn't
> exist from the host's previous reading.
> 
> If the Namespace Attach occurs to an ANA group the host already knows
> about, then you don't need to send an ANA AEN because there's nothing
> new in the log that the host requires. You just need to send the NS
> Notify AEN.
> 
> But if a side effect of attaching a namespace results in a new ANA group
> becoming visible to the host, then that group creation is considered a
> separate event, so the host wants both AENs. I believe this is where
> Christoph is trying to steer the interpretation and the text.

Exactly.  Although as Hannes pointed out, this language:

  If, for an ANA Group, there are no namespaces attached to the
  controller processing the command, then no ANA Group Descriptor is
  returned for that ANA Group (i.e., an ANA Group Descriptor is returned
  only if that ANA Group contains namespaces that are attached to the
  controller processing the command.

creates a bit of a chicken an egg problem in that case of a newly
attached namespace that is the first one referencing an ANA group.