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

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Wei Liu writes ("Re: [PATCH v11 20/27] Support colo mode for qemu disk"):
> Supporting PV guest is certainly going to be non-trivial. And I don't
> think we would ever ask you to actually implement that.

Indeed.

> The point is to have a story that when other people want to implement
> COLO for PV-aware guests (PVHVM, PV and PVH), they are not crippled by
> existing interfaces.
> 
> Currently the disk spec seems to be designed exclusively for QEMU. This
> is not very desirable, but at least it wouldn't stop people from either
> reusing them or inventing new parameters.

I think in fact (following some in-person conversations) that I am
comfortable with this implementation requiring qemu right now.

Future PV[H] COLO arrangements might well use qdisk anyway.  I think
it is OK for libxl to decide that qemu is needed in this case.  All
that's needed now is to arrange that: if someone, in the future, wants
to make a version of COLO that works without qemu somehow then they
can do that without having to significantly change the libxl API.

So all that's needed is for the interface to libxl not to imply that
qemu is in use.  I don't think the interface proposed here implies
that qemu is in use.

The proposed interface seems to mostly speak about things which are
not qemu-specific, so it's probably OK.

Ian.

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