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Re: [Qemu-block] [Qemu-devel] [PATCH v4 00/27] block: Lock images when o
From: |
Daniel P. Berrange |
Subject: |
Re: [Qemu-block] [Qemu-devel] [PATCH v4 00/27] block: Lock images when opening |
Date: |
Wed, 11 May 2016 09:52:58 +0100 |
User-agent: |
Mutt/1.6.0 (2016-04-01) |
On Wed, May 11, 2016 at 10:04:12AM +0200, Markus Armbruster wrote:
> "Daniel P. Berrange" <address@hidden> writes:
>
> > 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.
> >>
> >> 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.
>
> Could a QEMU + libvirt together provide both safe and unsafe read-only
> access? Safe means you get consistent data. Unsafe means you're taking
> your chances.
>
> Libguestfs could then use unsafe if the user asks for it. Or even by
> default; that's really libguesfs's business.
>
> Backward compatibility may complicate things, but getting into a
> reasonable state is sometimes worth a lengthy and somewhat messy
> transition.
We would have to use 'nolock' by default, and provide apps an opt-in
config flag to request locking of r/o images if they wanted it.
Regards,
Daniel
--
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- Re: [Qemu-block] [Qemu-devel] [PATCH v4 00/27] block: Lock images when opening, (continued)
- Re: [Qemu-block] [Qemu-devel] [PATCH v4 00/27] block: Lock images when opening, Daniel P. Berrange, 2016/05/10
- Re: [Qemu-block] [Qemu-devel] [PATCH v4 00/27] block: Lock images when opening, Kevin Wolf, 2016/05/10
- Re: [Qemu-block] [Qemu-devel] [PATCH v4 00/27] block: Lock images when opening, Richard W.M. Jones, 2016/05/10
- Re: [Qemu-block] [Qemu-devel] [PATCH v4 00/27] block: Lock images when opening, Kevin Wolf, 2016/05/10
- Re: [Qemu-block] [Qemu-devel] [PATCH v4 00/27] block: Lock images when opening, Richard W.M. Jones, 2016/05/10
- Re: [Qemu-block] [Qemu-devel] [PATCH v4 00/27] block: Lock images when opening, Kevin Wolf, 2016/05/10
- Re: [Qemu-block] [Qemu-devel] [PATCH v4 00/27] block: Lock images when opening, Richard W.M. Jones, 2016/05/10
- Re: [Qemu-block] [Qemu-devel] [PATCH v4 00/27] block: Lock images when opening, Daniel P. Berrange, 2016/05/10
- Re: [Qemu-block] [Qemu-devel] [PATCH v4 00/27] block: Lock images when opening, Kevin Wolf, 2016/05/10
- Re: [Qemu-block] [Qemu-devel] [PATCH v4 00/27] block: Lock images when opening, Markus Armbruster, 2016/05/11
- Re: [Qemu-block] [Qemu-devel] [PATCH v4 00/27] block: Lock images when opening,
Daniel P. Berrange <=
- Re: [Qemu-block] [Qemu-devel] [PATCH v4 00/27] block: Lock images when opening, Fam Zheng, 2016/05/11
- Re: [Qemu-block] [Qemu-devel] [PATCH v4 00/27] block: Lock images when opening, Richard W.M. Jones, 2016/05/11
- Re: [Qemu-block] [Qemu-devel] [PATCH v4 00/27] block: Lock images when opening, Kevin Wolf, 2016/05/11
- Re: [Qemu-block] [Qemu-devel] [PATCH v4 00/27] block: Lock images when opening, Daniel P. Berrange, 2016/05/10
- Re: [Qemu-block] [Qemu-devel] [PATCH v4 00/27] block: Lock images when opening, Kevin Wolf, 2016/05/10
- Re: [Qemu-block] [Qemu-devel] [PATCH v4 00/27] block: Lock images when opening, Richard W.M. Jones, 2016/05/10
Re: [Qemu-block] [PATCH v4 00/27] block: Lock images when opening, Richard W.M. Jones, 2016/05/11