[Qemu-devel] Loading snapshot with readonly qcow2 image

[Michael Spradling <michael@os.amperecomputing.com>]

Hello,

I would like to resume a snapshot via the command line option -loadvm
with a read only QCOW2 file.  For my use case, I would ideally like to
load multiple instances of different snapshots from the same QCOW2 image.

It seems this is not possible at the moment as when a snapshot is loaded, QEMU
copies some meta data around in the qcow2 image.

I have also tried to use the "-snapshot" option, which to my understanding
creates a new temporary QCOW2 file with a backing file pointing the original
image passed on the command line.  This also does not work, when looking
through the source it appears QEMU only supports loading snapshots from writable
QCOW2 images and doesn't support loading from images in backing files.

My question is has anyone looked into loading snapshots from a backing
file?  I have attempted to look through the code and this looks to be
difficult.  If I attempt to add support for this is there any general
advice to follow?  Any other ideas?

Thanks,
Michael