Re: [Xen-devel] [PATCH RESEND] tools/libxl: add support for emulated NVMe drives

[Ian Jackson <ian.jackson@xxxxxxxxxxxxx>]

Paul Durrant writes ("RE: [PATCH RESEND] tools/libxl: add support for emulated 
NVMe drives"):
> This is my VM:
> 
> root@brixham:~# xenstore-ls "/libxl/3"
> device = ""
>  vbd = ""
>   51712 = ""
...
>    params = "qcow2:/root/winrs2-pv1.qcow2"

> No problem using xvda... still ends up as IDE primary master.

Right.  The question is more whether this confuses the guest.  I don't
think the tools will actually mind.

I guess that was with xapi rather than libxl ?

> > So maybe they should reuse the hd* numbering ?
> 
> That might be too limiting. The hd* numbering scheme doesn't stretch
> very far.

Indeed.  sd is rather limited too.

But, you say:

      Also, current versions of SeaBIOS do not support booting from
      NVMe devices, so the vdev should only be used for secondary drives.

So currently this is mostly useful for testing ?

Normally the emulated devices are _intended_ for bootstrapping to an
environment that can handle vbds.  Which doesn't involve having very
many of them.

> > > That means modifications to PV frontends would be needed, which is
> > > going to make things more difficult. Most OS find disks by UUID
> > > these days anyway so I'm still not sure that just using xvd*
> > > numbering would really be a problem.
> > 
> > In terms of the "nominal disk type" discussed in
> > xen-vbd-interface.markdown.7, I don't think these emulated devices,
> > which get unplugged, should be have a "nomainl disk type" of "Xen
> > virtual disk".
> 
> Ok. I'll submit another patch to QEMU to distinguish between
> IDE/SCSI disks and NVMe disks in the unplug protocol, come up with a
> new PV numbering schemed and modify the Windows frontend to
> understand it.

Before you go away and do a lot of work, perhaps we should keep
exploring whether my concerns are actualliy justified...

Allocating a new numbering scheme might involve changing Linux guests
too.  (I haven't experimented with what happens if one specifies a
reserved number.)

Ian.

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