Re: [Xen-devel] [PATCH v11 20/27] Support colo mode for qemu disk

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Konrad Rzeszutek Wilk writes ("Re: [PATCH v11 20/27] Support colo mode for qemu 
disk"):
> On Fri, Mar 04, 2016 at 05:52:09PM +0000, Ian Jackson wrote:
> > How can this be made to work with PV guests ?
> 
> QEMU can also serve PV guests (qdisk).

Yes.

> I think your question is more of - what about making this work with
> PV block backend?

Yes.

> > What if an HVM guest has PV-on-HVM drivers ?  In this case there might
> > be two relevant qemus, one for the qdisk Xen PV block backend, and one
> > for the emulated IDE.
> 
> In both cases QEMU would use the same underlaying API to actually write/read
> out the blocks. That API would then use NBD, etc to replicate writes.
> 
> Maybe a little ASCII art?
> 
>       qdisk  ide
>         \    /
>          \  /
>          block API
>           |
>          QCOW2
>           |
>          NBD

Except that currently libxl may launch two qemus: one to serve
emulated ide requests, and one to service PV qdisk.

Ian.

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