I recently ran into an issue where I found I couldn't combine the -loadvm and -snapshot flags, nor any conceivable combination of alternate approaches like loadvm via the monitor. Independently, both options work as expected, but together I get this error:
qemu-system-x86_64: Device 'virtio0' does not have the requested snapshot 'base' The goal here is to resume the VM state from a snapshot, but to prevent the guest from persisting writes to the underlying qcow2. I started digging into the code to understand this problem more, and I was pretty deep in the weeds when I realized what the underlying problem probably was and the kind of refactoring necessary to fix it - so I'm here to touch base before moving any further. I believe this happens because -snapshot creates a temporary qcow2 overlaid on top of the disk you're using, and this overlay does not have any snapshots copied, nor does any of the snapshot reading code (e.g. qcow2_snapshot_list or qcow2_snapshot_goto) iterate over backing disks to load their snapshots. At first I was going to adjust the qcow2 snapshot loading code (those two functions in particular) to read through their backends, but I'm a little unfamiliar with this code and the refactoring is not minor so I would like to get feedback from some of the wiser folks on this mailing list before I sink too much time into this. Thoughts? -- Drew DeVault
