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?