Re: [PATCH 5/6] migration: support excluding block devs in QMP snapshot commands

[Kevin Wolf]

Am 02.07.2020 um 19:57 hat Daniel P. Berrangé geschrieben:
> This wires up support for a new "exclude" parameter to the QMP commands
> for snapshots (savevm, loadvm, delvm). This parameter accepts a list of
> block driver state node names.
> 
> One use case for this would be a VM using OVMF firmware where the
> variables store is a raw disk image. Ideally the variable store would be
> qcow2, allowing its contents to be included in the snapshot, but
> typically today the variable store is raw. It is still useful to be able
> to snapshot VMs using OVMF, even if the varstore is excluded, as the
> main OS disk content is usually the stuff the user cares about.
> 
> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

Wouldn't it be better to take an optional list of nodes to _include_
that just defaults to our current set of nodes?

The problem with excluding is that we already don't snapshot many nodes,
and the criteria to choose the right ones weren't entirely obvious, so
we just went with something that seemed to make the most sense. But the
management application may actually want to snapshot more nodes than we
cover by default.

I feel things become clearer and less surprising if the client just
tells us explicitly which images are supposed to be snapshotted instead
of adding exceptions on top of a default selection that we're already
not really sure about.

Kevin