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Re: [Xen-devel] [PATCH v1] unmodified_drivers: unplug the emulated devices at resume time

On Tue, 12 Jun 2018, Jan Beulich wrote:
> >>> On 12.06.18 at 16:10, <olaf@xxxxxxxxx> wrote:
> > Since qemu-2.10 it is required to unplug emulated devices again after
> > a live migration. If this is not done, qemu's block-backend driver
> > will be unable to open the backing disk image because it is still busy
> > by qemu's IDE driver. As a result the domUs block-frontend driver will
> > be unable to access the disks, and the domU has to be destroyed.
> > libxl is unable to detect the situation.
> So there's no plan to fix this on the qemu side?
> > Apply the same workaround for this qemu bug that was done already
> > years ago in linux.git with commit 512b109ec962 ("xen: unplug the
> > emulated devices at resume time") to make sure xenlinux based domUs
> > can be migrated to unfixed hosts.
> Hmm, that change has no explanation whatsoever of why this was
> necessary already back at that time. Stefano?

It was too long ago, I don't remember exactly, but my guess is that the
presence of the emulated devices at resume time was causing problems to
Linux. Given that Linux HVM was supposed to be able to run on older
versions of Xen, the workaround was put in Linux rather than Xen. (I
wonder if the Windows PV drivers have also something similar.)

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