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

[Paul Durrant <Paul.Durrant@citrix.com>]

> -----Original Message-----
> From: Wei Liu [mailto:wei.liu2@citrix.com]
> Sent: 18 January 2017 12:02
> To: Paul Durrant <Paul.Durrant@citrix.com>
> Cc: Wei Liu <wei.liu2@citrix.com>; xen-devel@lists.xenproject.org; Ian
> Jackson <Ian.Jackson@citrix.com>
> Subject: Re: [PATCH RESEND] tools/libxl: add support for emulated NVMe
> drives
> 
[snip]
> > > >
> > > > -   For HVM guests, each whole-disk hd* and and sd* device is made
> > > > -   available _both_ via emulated IDE resp. SCSI controller, _and_ as a
> > > > -   Xen VBD.  The HVM guest is entitled to assume that the IDE or SCSI
> > > > -   disks available via the emulated IDE controller target the same
> > > > +   For HVM guests, each whole-disk hd*, sd* or nvme* device is made
> > > > +   available _both_ via emulated IDE, SCSI controller or NVMe drive
> > > > +   respectively _and_ as a Xen VBD.  The HVM guest is entitled to
> > > > +   assume that the disks available via the emulation target the same
> > >
> > > How do you expect the guest to deal with multipath NVMe devices?
> Maybe
> > > we need to add unplug support for NVMe devices in QEMU?
> >
> > That's true. For convenience, there would need to a QEMU patch for
> unplug to allow displacement of the emulated device with PV. I can
> document this as a shortcoming at the moment, if that's ok?
> >
> 
> The unplug functionality, as I understand, is crucial to data integrity.
> Documenting this as shortcoming doesn't seem to be good enough.  Do we
> need to wait until QEMU is ready before we can apply this patch?

It will take time to get a patch into QEMU and if you're going to use PV drivers then you have little interest in the emulation model. I think just documenting it would be ok. For safety I guess I could explore the possibility of having libxl not create a PV backend for this vdev type.

  Paul

> 
> Wei.
> 
> 
> >   Paul

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