Re: [PATCH] hw/block/nvme: re-enable NVMe PCI hotplug

[Hannes Reinecke]

On 5/11/21 3:37 PM, Klaus Jensen wrote:
> On May 11 15:12, Hannes Reinecke wrote:
>> On 5/11/21 2:22 PM, Klaus Jensen wrote:
[ .. ]
>>> The hotplug fix looks good - I'll post a series that tries to integrate
>>> both.
>>>
>> Ta.
>>
>> The more I think about it, the more I think we should be looking into
>> reparenting the namespaces to the subsystem.
>> That would have the _immediate_ benefit that 'device_del' and
>> 'device_add' becomes symmetric (ie one doesn't have to do a separate
>> 'device_add nvme-ns'), as the nvme namespace is not affected by the
>> hotplug event.
>>
> 
> I have that working, but I'm struggling with a QEMU API technicality in
> that I apparently cannot simply move the NvmeBus creation to the
> nvme-subsys device. For some reason the bus is not available for the
> nvme-ns devices. That is, if one does something like this:
> 
>   -device nvme-subsys,...
>   -device nvme-ns,...
> 
> Then I get an error that "no 'nvme-bus' bus found for device 'nvme'ns".
> This is probably just me not grok'ing the qdev well enough, so I'll keep
> trying to fix that. What works now is to have the regular setup:
> 
_Normally_ the 'id' of the parent device spans a bus, so the syntax
should be

-device nvme-subsys,id=subsys1,...
-device nvme-ns,bus=subsys1,...

As for the nvme device I would initially expose any namespace from the
subsystem to the controller; the nvme spec has some concept of 'active'
or 'inactive' namespaces which would allow us to blank out individual
namespaces on a per-controller basis, but I fear that's not easy to
model with qdev and the structure above.

>   -device nvme-subsys,...
>   -device nvme,...
>   -device nvme-ns,...
> 
> And the nvme-ns device will then reparent to the NvmeBus on nvme-subsys
> (which magically now IS available when nvme-ns is realized). This has
> the same end result, but I really would like that the namespaces could
> be specified as children of the subsys directly.
> 
Shudder.
Automatic reparenting.
To my understanding from qdev that shouldn't even be possible.
Please don't.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                     Kernel Storage Architect
hare@suse.de                                   +49 911 74053 688
SUSE Software Solutions Germany GmbH, 90409 Nürnberg
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