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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 12.06.18 at 21:39, <sstabellini@xxxxxxxxxx> wrote:
> 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.)

Paul?

Thanks, Jan



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