Re: [Qemu-block] [Qemu-devel] [PATCH 1/2] Add save-snapshot, load-snapshot and delete-snapshot to QAPI

[Max Reitz]

On 2018-01-08 14:52, Eric Blake wrote:
> On 01/07/2018 06:23 AM, Richard Palethorpe wrote:
>> Add QAPI wrapper functions for the existing snapshot functionality. These
>> functions behave the same way as the HMP savevm, loadvm and delvm
>> commands. This will allow applications, such as OpenQA, to programmatically
>> revert the VM to a previous state with no dependence on HMP or qemu-img.
> 
> That's already possible; libvirt uses QMP's human-monitor-command to
> access these HMP commands programmatically.
> 
> We've had discussions in the past about what it would take to have
> specific QMP commands for these operations; the biggest problem is that
> these commands promote the use of internal snapshots, and there are
> enough performance and other issues with internal snapshots that we are
> not yet ready to commit to a long-term interface for making their use
> easier.  At this point, our recommendation is to prefer external snapshots.

We already have QMP commands for internal snapshots, though.  Isn't the
biggest issue that savevm takes too much time to be a synchronous QMP
command?

Max

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