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Re: [Qemu-devel] storing machine data in qcow images?

From: Richard W.M. Jones
Subject: Re: [Qemu-devel] storing machine data in qcow images?
Date: Thu, 24 May 2018 16:20:14 +0100
User-agent: Mutt/1.5.21 (2010-09-15)

On Thu, May 24, 2018 at 05:08:17PM +0200, Kevin Wolf wrote:
> Am 24.05.2018 um 16:56 hat Michael S. Tsirkin geschrieben:
> > On Thu, May 24, 2018 at 12:32:51PM +0100, Richard W.M. Jones wrote:
> > > There is however a seed of a good idea in the thread:
> > > 
> > > > I don't think QEMU needs to use this information automatically,
> > > > necessarily.  I think the first step is to simply make QEMU save
> > > > this information in the disk image, and making qemu-img able to
> > > > read and write this information.
> > > 
> > > It would be nice if qcow2 added arbitrary data sections (which would
> > > always be ignored by qemu) for storing additional data.  This could be
> > > used to create a compact qcow2 + metadata format to rival OVA for
> > > management layers to use, and there are various other uses too.
> > > 
> > > Rich.
> > 
> > I think this part is pretty uncontroversial.
> > 
> > But can we add data without changing the verion?
> Yes. Don't worry about where to store it, we'll solve this. Do worry
> about what to store.

Ideally from my point of view: named blobs.  More formally, any number
of (key, value) pairs where the key is a simple string, and the value
is a binary blob.  The binary blobs might really be XML or YAML or an
icon or whatever, but qemu would not need to look inside them.

We could then attach metadata (in some to-be-decided format) to qcow2
files and create a compact rival to OVA without needing to encode any
knowledge of the metadata into qemu at all.

Another use for this is allowing qcow2 files to contain names, titles,
descriptions, creation date, OS icons, etc. which could be displayed
in file managers.


Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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