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Re: [Qemu-devel] Qemu savevm and CPU soft lockup

From: Anthony Liguori
Subject: Re: [Qemu-devel] Qemu savevm and CPU soft lockup
Date: Thu, 24 Sep 2009 11:20:39 -0500
User-agent: Thunderbird (X11/20090825)

Kevin Wolf wrote:
Am 24.09.2009 00:28, schrieb Anthony Liguori:
Jamie Lokier wrote:
This is normal savevm behaviour, and it is exactly the reason why
migrate-to-file is useful.  I would not be surprised if savevm is
changed to use migrate-to-file internally at some point, but it does
not look like happening soon.
It's the same infrastructure. The reason savevm isn't live is that savevm stores it's data in a qcow2 file. Right now the way qcow2 is structured, the snapshot has to be a fixed size and allocated at once. In order to make savevm live, we need a method to stream savevm data to a qcow2 file while still allowing other IO operations to that qcow2 file.

I'm fairly sure this will require a change to the qcow2 format in order to support this.

Hm, snapshots are nothing complicated from qcow2 perspective. Why do you
think data needs to be fixed size?

What happens if you're in the middle of writing snapshot data and another cluster has to be allocated? You'll need a way to store the snapshot data discontinuously.


Anthony Liguori

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