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

[Christoph Hellwig]

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.