On 04/09/2013 10:04 AM, Markus Armbruster wrote: >> + >> +## >> +# @vm-snapshot-save: >> +# >> +# Create a snapshot of the whole virtual machine. If tag is provided as >> @name, >> +# it is used as human readable identifier. If there is already a snapshot >> +# with the same tag or id, the force argument needs to be true to replace >> it. > > "tag or id"? > > HMP command savevm's argument is matched against both QEMUSnapshotInfo > member id_str (a.k.a. id) and name (a.k.a. tag). Do we really want that > kind of overloading in QMP? Shouldn't we make it tag vs. id explicit > there?
The qcow2 file format already allows for the creation of a snapshot with an id but no tag. We've been back and forth about whether QMP should allow a user to be able to create all valid qcow2 files (and hence allow the omission of tag). But things really get confusing if you allow the creation of a tag that matches an existing id (create a snapshot, then create another snapshot with the tag '1'); or even if a tag can match a potential future id (create a snapshot with a tag named '2', then create another snapshot). So the lookup should always check for BOTH tag and id, even though the command is supplying only a 'tag'; and if a tag is omitted, a unique id will always be returned. > >> +# >> +# The VM is automatically stopped and resumed and saving a snapshot can take >> +# a long time. >> +# >> +# @name: #optional tag of new snapshot or tag|id of existing snapshot > > Should we make this mandatory? We have to keep the argument optional in > HMP, but that needn't concern us here. If we mandate that a tag always be supplied, then we cannot create qcow2 files with a snapshot that lacks a tag using just QMP; but even if we do that, we STILL have to support use of existing qcow2 files that were created by earlier qemu and/or other tools that have snapshots without a tag. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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