Cc'ing the QCOW2 folks. Drew DeVault <s...@cmpwn.com> writes:
> 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
