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Message-ID: <4EB96829.1010709@suse.de>
Date:	Tue, 08 Nov 2011 18:34:33 +0100
From:	Alexander Graf <agraf@...e.de>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Avi Kivity <avi@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	"linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org list" <kvm@...r.kernel.org>,
	qemu-devel Developers <qemu-devel@...gnu.org>,
	Pekka Enberg <penberg@...nel.org>,
	Am?rico Wang <xiyou.wangcong@...il.com>,
	Blue Swirl <blauwirbel@...il.com>
Subject: Re: [PATCH] KVM: Add wrapper script around QEMU to test kernels

On 11/08/2011 03:59 PM, Christoph Hellwig wrote:
> On Tue, Nov 08, 2011 at 04:57:04PM +0200, Avi Kivity wrote:
>>> Running qemu -snapshot on the actual root block device is the only
>>> safe way to reuse the host installation, although it gets a bit
>>> complicated if people have multiple devices mounted into the namespace.
>> How is -snapshot any different?  If the host writes a block after the
>> guest has been launched, but before that block was cowed, then the guest
>> will see the new block.
> Right, thinko - qemu's snapshots are fairly useless due to sitting
> ontop of the file to be modified.
>
>> It could work with a btrfs snapshot, but not everyone uses that.
> Or LVM snapshot.  Either way, just reusing the root fs without care
> is a dumb idea, and I really don't want any tool or script that
> encurages such braindead behaviour in the kernel tree.

Heh, yeah, the intent was obviously to have a separate rootfs tree 
somewhere in a directory. But that's not available at first when running 
this, so I figured for a simple "get me rolling" FAQ directing the 
guest's rootfs to / at least gets you somewhere (especially when run as 
user with init=/bin/bash).

Alex

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