v4 includes Federico's drive-reopen (patch 10) command, fixes another
small bug in Jeff's code (patch 2), and tweaks the union handling for
older compilers.
v3 tested with the following scenarios, v4 only d/e:
a) mirror only
1) create base.qcow2 and starat QEMU with it
2) Execute the following QMP command
{ "execute": "qmp_capabilities" }
{ "execute": "transaction", "arguments":
{'actions': [
{ 'type': 'drive-mirror', 'data' :
{ 'device': 'ide0-hd0', 'target': '/home/pbonzini/mirror.qcow2' } } ] } }
{ "execute": "cont" }
3) hibernate the guest (this requires an IDE disk and -cpu kvm64,-kvmclock)