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Re: [Qemu-devel] [PATCH 1/5] block: added lock image option and callback
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] [PATCH 1/5] block: added lock image option and callback |
Date: |
Tue, 12 Jan 2016 13:28:06 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
Am 12.01.2016 um 12:33 hat Fam Zheng geschrieben:
> On Tue, 01/12 11:10, Kevin Wolf wrote:
> >
> > The problem is that libvirt already takes a lock, as Dan mentioned in
> > another reply in this thread, so we can't enable locking in qemu by
> > default. It would always fail when run under libvirt.
> >
> > Unless I'm seriously mistaken, this means that flock() inside qemu is
> > dead.
>
> Yes, I see the problem with libvirt, but can we instead do these?
>
> 1) Do a soft flock() in QEMU invocation. If it fails, sliently ignore.
> 2) Do a hard flock() in qemu-img invocation. If it fails, report and exit.
>
> This way, if libvirt is holding flock, we can assume libvirt is actually
> "using" the image: 1) just works as before, but 2) will not break the qcow2.
> That is still a slight improvement, and does solve the reckless "qemu-img
> snapshot create" user's problem.
This makes two assumptions:
1. qemu is only ever invoked by libvirt
2. qemu-img is only ever invoked by human users
Both of them are wrong. 1. just means that manually started QEMUs are
unprotected (which is already bad), but 2. means that qemu-img called by
libvirt fails (which is obviously not acceptable).
Kevin
- Re: [Qemu-devel] [PATCH 1/5] block: added lock image option and callback, (continued)
Re: [Qemu-devel] [PATCH 1/5] block: added lock image option and callback, Denis V. Lunev, 2016/01/12
- Re: [Qemu-devel] [PATCH 1/5] block: added lock image option and callback, Kevin Wolf, 2016/01/12
- Re: [Qemu-devel] [PATCH 1/5] block: added lock image option and callback, Fam Zheng, 2016/01/12
- Re: [Qemu-devel] [PATCH 1/5] block: added lock image option and callback, Denis V. Lunev, 2016/01/12
- Re: [Qemu-devel] [PATCH 1/5] block: added lock image option and callback,
Kevin Wolf <=
- Re: [Qemu-devel] [PATCH 1/5] block: added lock image option and callback, Fam Zheng, 2016/01/12
- Re: [Qemu-devel] [PATCH 1/5] block: added lock image option and callback, Daniel P. Berrange, 2016/01/12
- Re: [Qemu-devel] [PATCH 1/5] block: added lock image option and callback, Fam Zheng, 2016/01/12
Re: [Qemu-devel] [PATCH 1/5] block: added lock image option and callback, Denis V. Lunev, 2016/01/12
Re: [Qemu-devel] [PATCH 1/5] block: added lock image option and callback, Fam Zheng, 2016/01/12
Re: [Qemu-devel] [PATCH 1/5] block: added lock image option and callback, Eric Blake, 2016/01/13
Re: [Qemu-devel] [PATCH 1/5] block: added lock image option and callback, Denis V. Lunev, 2016/01/14