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Re: [Qemu-devel] [Qemu-block] [PATCH 00/10] qcow2: Implement image locki

From: Denis V. Lunev
Subject: Re: [Qemu-devel] [Qemu-block] [PATCH 00/10] qcow2: Implement image locking
Date: Wed, 23 Dec 2015 18:08:45 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.4.0

On 12/23/2015 05:57 PM, Vasiliy Tolstov wrote:
2015-12-22 19:46 GMT+03:00 Kevin Wolf <address@hidden>:
Enough innocent images have died because users called 'qemu-img snapshot' while
the VM was still running. Educating the users doesn't seem to be a working
strategy, so this series adds locking to qcow2 that refuses to access the image
read-write from two processes.

Eric, this will require a libvirt update to deal with qemu crashes which leave
locked images behind. The simplest thinkable way would be to unconditionally
override the lock in libvirt whenever the option is present. In that case,
libvirt VMs would be protected against concurrent non-libvirt accesses, but not
the other way round. If you want more than that, libvirt would have to check
somehow if it was its own VM that used the image and left the lock behind. I
imagine that can't be too hard either.

This breaks ability to create disk only snapshot while vm is running.
Or i miss something?

you should do this by asking running QEMU not by
qemu-img, which is badly wrong.


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