Re: [Qemu-devel] [Qemu-block] [RFC] nvme: how to support multiple namespaces

[Klaus Birkelund <klaus@birkelund.eu>]

On Thu, Jun 20, 2019 at 05:37:24PM +0200, Laszlo Ersek wrote:
> On 06/17/19 10:12, Klaus Birkelund wrote:
> > Hi all,
> > 
> > I'm thinking about how to support multiple namespaces in the NVMe
> > device. My first idea was to add a "namespaces" property array to the
> > device that references blockdevs, but as Laszlo writes below, this might
> > not be the best idea. It also makes it troublesome to add per-namespace
> > parameters (which is something I will be required to do for other
> > reasons). Some of you might remember my first attempt at this that
> > included adding a new block driver (derived from raw) that could be
> > given certain parameters that would then be stored in the image. But I
> > understand that this is a no-go, and I can see why.
> > 
> > I guess the optimal way would be such that the parameters was something
> > like:
> > 
> >    -blockdev raw,node-name=blk_ns1,file.driver=file,file.filename=blk_ns1.img
> >    -blockdev raw,node-name=blk_ns2,file.driver=file,file.filename=blk_ns2.img
> >    -device nvme-ns,drive=blk_ns1,ns-specific-options (nsfeat,mc,dlfeat)...
> >    -device nvme-ns,drive=blk_ns2,...
> >    -device nvme,...
> > 
> > My question is how to state the parent/child relationship between the
> > nvme and nvme-ns devices. I've been looking at how ide and virtio does
> > this, and maybe a "bus" is the right way to go?
> 
> I've added Markus to the address list, because of this question. No
> other (new) comments from me on the thread starter at this time, just
> keeping the full context.
> 

Hi all,

I've succesfully implemented this by introducing a new 'nvme-ns' device
model. The nvme device creates a bus named from the device id ('id'
parameter) and the nvme-ns devices are then registered on this.

This results in an nvme device being creates like this (two namespaces
example):

  -drive file=nvme0n1.img,if=none,id=disk1
  -drive file=nvme0n2.img,if=none,id=disk2
  -device nvme,serial=deadbeef,id=nvme0
  -device nvme-ns,drive=disk1,bus=nvme0,nsid=1
  -device nvme-ns,drive=disk2,bus=nvme0,nsid=2

How does that look as a way forward?

Cheers,
Klaus