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

From: Max Reitz <mreitz@redhat.com>
To: "Eduardo Habkost" <ehabkost@redhat.com>,
	"Daniel P. Berrangé" <berrange@redhat.com>
Cc: "Michal Suchánek" <msuchanek@suse.de>,
	"Kevin Wolf" <kwolf@redhat.com>,
	qemu-block@nongnu.org, "Michael S. Tsirkin" <mst@redhat.com>,
	"Richard W.M. Jones" <rjones@redhat.com>,
	qemu-devel@nongnu.org, stefanha@redhat.com
Subject: Re: [Qemu-devel] storing machine data in qcow images?
Date: Wed, 6 Jun 2018 16:21:28 +0200	[thread overview]
Message-ID: <9a7567dd-5813-8a5a-b079-ae198e5394a5@redhat.com> (raw)
In-Reply-To: <20180606141432.GS7451@localhost.localdomain>

[-- Attachment #1: Type: text/plain, Size: 2019 bytes --]

On 2018-06-06 16:14, Eduardo Habkost wrote:
> On Wed, Jun 06, 2018 at 02:50:10PM +0100, Daniel P. Berrangé wrote:
>> On Wed, Jun 06, 2018 at 03:45:10PM +0200, Michal Suchánek wrote:
>>>
>>> I think that *if* we want an 'appliance' format that stores a whole VM
>>> in a single file to ease VM distribution then the logical place to look
>>> in qemu is qcow. The reason have been explained at length.
>>
>> I rather disagree. This is a common problem beyond just QEMU and everyone
>> just uses an existing archive format (TAR, ZIP) for bundling together
>> one or more disk images, metdata for config, and whatever other resources
>> are applicable for the vendor.  This works with any disk format (raw,
>> qcow2, vmdk, vpc, etc) so is preferrable to inventing someting that is
>> specific to qcow2 IMHO.
> 
> Now we have N+1 appliance file formats.  :)
> 
> (We like it or not, qcow2 is already used as an appliance format
> for single-disk VMs in practice.)
> 
> But I agree this must not be specific to qcow2.  The same VM
> description format we agree upon should work with other disk
> formats or with multi-disk appliances.
> 
> If we specify a reasonable VM description format for appliances
> and make it work inside (e.g.) tar files, we will still have the
> option of allowing the description be placed inside qcow2 if we
> really want to.  I don't think we need to finish this qcow2
> bikeshedding exercise right now.

That actually sounds reasonable to me.

I better not think about it for too long so I don't come up with
something I very much dislike about it.

(Well, now I have.  The thing I still dislike is that we haven't talked
about what we actually want in the end.  Do we want just the very basic
configuration options that are portable?  But what really is the use
case for such basic information?  Won't people demand ever more
configuration options, then?  I certainly would.

And having to handle a full-blown config is probably a pain...)

Max

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 488 bytes --]