Re: [Qemu-devel] [Qemu-block] [RFC, v1] Namespace Management Support

[Klaus Birkelund]

On Tue, Jul 02, 2019 at 10:39:36AM -0700, Matt Fitzpatrick wrote:
> Adding namespace management support to the nvme device. Namespace creation
> requires contiguous block space for a simple method of allocation.
> 
> I wrote this a few years ago based on Keith's fork and nvmeqemu fork and
> have recently re-synced with the latest trunk.  Some data structures in
> nvme.h are a bit more filled out that strictly necessary as this is also the
> base for sr-iov and IOD patched to be submitted later.
> 

Hi Matt,

Nice! I'm always happy when new features for the nvme device is posted!

I'll be happy to review it, but I won't start going through it in
details because I believe the approach to supporting multiple namespaces
is flawed. We had a recent discussion on this and I also got some
unrelated patches rejected due to implementing it similarly by carving
up the image.

I have posted a long series that includes a patch for multiple
namespaces. It is implemented by introducing a fresh `nvme-ns` device
model that represents a namespace and attaches to a bus created by the
parent `nvme` controller device.

The core issue is that a qemu image /should/ be attachable to other
devices (say ide) and not strictly tied to the one device model. Thus,
we cannot just shove a bunch of namespaces into a single image.

But, in light of your patch, I'm not convinced that my implementation is
the correct solution. Maybe the abstraction should not be an `nvme-ns`
device, but a `nvme-nvm` device that when attached changes TNVMCAP and
UNVMCAP? Maybe you have some input for this? Or we could have both and
dynamically create the nvme-ns devices on top of nvme-nvm devices. I
think it would still require a 1-to-1 mapping, but it could be a way to
support the namespace management capability.


Cheers,
Klaus