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Re: [Qemu-devel] PATCH: Control over drive open modes for backing file
From: |
Jamie Lokier |
Subject: |
Re: [Qemu-devel] PATCH: Control over drive open modes for backing file |
Date: |
Thu, 31 Jul 2008 19:59:56 +0100 |
User-agent: |
Mutt/1.5.13 (2006-08-11) |
Anthony Liguori wrote:
> So while I think it's valid to have a "read-only disk" exposed to the
> guest, I don't think the user should have anything to do with how we
> open the file.
All good points.
My concern (and it may be different to others) is when I branch an
image using a qcow2 with backing qcow (perhaps more than two deep).
The backing image is sometimes shared with other branches.
E.g. I might have a full install of an OS, and then have a branch
where I install software package A, and another branch with software
package B. Both share the same base image.
In these, it's very important that I don't accidentally modify the
base image. E.g. if I foolishly entered the 'commit' monitor command
in VM A, I'd *corrupt* the disk of VM B.
So it would be nice to open the base image read-only.
(Microsoft have a similar description in their documentation on 'disk
image differencing for maintaining test systems' for Virtual PC).
Now savevm snapshots (as opposed to -snapshot) confuse this picture.
Can I arbitrarily branch off different snapshots within a single qcow2
file? Can I delete the 'base' snapshots safely? Most important: what
happens if I have snapshots in a qcow2 file which has a base file, and
I type 'commit'? Does it corrupt all the snapshots, effectively?
I find the snapshot facility a bit unclear as to what _exactly_ it
does to be honest, and am therefore wary of it.
Thanks,
-- Jamie
- Re: [Qemu-devel] PATCH: Control over drive open modes for backing file, (continued)
- Re: [Qemu-devel] PATCH: Control over drive open modes for backing file, Daniel P. Berrange, 2008/07/31
- Re: [Qemu-devel] PATCH: Control over drive open modes for backing file, Paul Brook, 2008/07/31
- Re: [Qemu-devel] PATCH: Control over drive open modes for backing file, Daniel P. Berrange, 2008/07/31
- Re: [Qemu-devel] PATCH: Control over drive open modes for backing file, Blue Swirl, 2008/07/31
- Re: [Qemu-devel] PATCH: Control over drive open modes for backing file, Jamie Lokier, 2008/07/31
- Re: [Qemu-devel] PATCH: Control over drive open modes for backing file, Daniel P. Berrange, 2008/07/31
- Re: [Qemu-devel] PATCH: Control over drive open modes for backing file, Blue Swirl, 2008/07/31
- Re: [Qemu-devel] PATCH: Control over drive open modes for backing file, Chris Wedgwood, 2008/07/31
Re: [Qemu-devel] PATCH: Control over drive open modes for backing file, Anthony Liguori, 2008/07/31
- Re: [Qemu-devel] PATCH: Control over drive open modes for backing file,
Jamie Lokier <=