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

[Hannes Reinecke]

On 12/9/20 5:19 PM, Keith Busch wrote:
> On Wed, Dec 09, 2020 at 05:02:05PM +0100, Hannes Reinecke wrote:
>> On 12/9/20 4:53 PM, Keith Busch wrote:
>>> On Wed, Dec 09, 2020 at 03:20:57PM +0000, Knight, Frederick wrote:
>>>> When a namespace is created (and contained in an ANA Group), the act
>>>> of creating that namespace results in a change to the ANA Log page -
>>>> therefore AEN.
>>>
>>> That is wrong: creating a namespace doesn't do anything to the ANA log.
>>> Only attached namespaces appear in the log. Creating a namespace
>>> doesn't result in automatically attaching it to any controller.
>>>
>>> You are thinking of Namespace Attach from section 5.19, and the spec
>>> doesn't define any special exceptions for events resulting from *that*
>>> command, which is also the command that triggered this thread.
>>>
>> Actually, no, we're not thinking about 'Namespace Attach'.
> 
> This patch is the result from an Attach command, otherwise the host
> driver wouldn't have found an unknown ANA group for a new namespace
> during the rescan.
> 
>> This is a normal namespace creation on the controller side.
>>
>> I do agree that 'Namespace Attach' would have different constrains and rules
>> under which AENs will be sent, but this is not what our initial use-case was
>> about.
> 
> The use case in this patch is about getting the host to recognize the
> ANA group of a newly attached namespace. If you stop at namespace
> creation, then this patch doesn't do anything.
> 
Now you got me confused.
Of course the namespace is attached to a controller, but this is _not_ 
the result of a 'namespace attach' command from the host.
If that's what you imply.
Not sure, though; as said, I'm confused now.

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.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
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