Re: [Qemu-devel] [PATCH] KVM: Add wrapper script around QEMU to test kernels

[Alexander Graf]

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