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Re: [Qemu-devel] [PATCH v4 00/27] block: Lock images when opening

From: Kevin Wolf
Subject: Re: [Qemu-devel] [PATCH v4 00/27] block: Lock images when opening
Date: Tue, 10 May 2016 14:45:57 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

Am 10.05.2016 um 14:22 hat Daniel P. Berrange geschrieben:
> On Tue, May 10, 2016 at 01:11:30PM +0100, Richard W.M. Jones wrote:
> > At no point did I say that it was safe to use libguestfs on live VMs
> > or that you would always get consistent data out.
> > 
> > But the fact that it can fail is understood, the chance of failure is
> > really tiny (it has literally only happened twice that I've read
> > corrupted data, in years of daily use), and the operation is very
> > useful.

Is it understood by you (which I'm happy to believe you) or by all of
your users (which I doubt)?

> > So I think this patch series should either not lock r/o VMs, or should
> > add a nolock flag to override the locking (which libguestfs will
> > always use).
> If QEMU locks r/o disks, then libvirt would likely end up setting the
> "nolock" flag unconditionally too, in order to avoid breaking libguestfs
> and other application usage of libvirt.

It would still have some value as we would protect command line users at
least. Of course I would prefer if libvirt could find a way to protect
their users as well without breaking valid use cases. But if we can
point at libvirt, I guess that's good for qemu at least...


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