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Re: [Xen-devel] libvirt, libxl and QDISKs

On Fri, 2013-04-26 at 12:31 +0100, Marek Marczykowski wrote:
> What about old good loop+phy based backend for file disk images? I don't want
> whole qemu in dom0 for PV domains, only for handling simple disk backend.
> Additionally sparse images + loop + phy + mount -o discard in domU makes the
> images "auto shrinking". Don't know if qemu is able to do this.

IIRC the problem with loop+phy is that loop doesn't do O_DIRECT and
therefore your data isn't actually on the disk when you might think it
is, which can lead to filesystem corruption even if the f/s is doing
correct barriers.

> Attached patch, which I currently use for that. If it is close to something
> that would be accepted, I will send it in new thread.

I think you can use a block script for this (i.e. it does the loop
mount) and avoid patching libxl at all. That's what xend did at least...


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