It should be created at VM creation time (or template changes commit).
But for example for HVM templates created before implementing
QubesOS/qubes-issues#1573, there would be no such image. So create it
when needed, just before VM startup
FixesQubesOS/qubes-issues#1602
We still can't support running HVM template and its VMs simultaneously
(easily), but still, have root-cow.img handled for HVM template, to
allow qvm-revert-template-changes.
FixesQubesOS/qubes-issues#1573
- QubesVmStorage provides now a default get_config_params() method which should
be enough for all possible Storage implementations.
- When writing a custom Storage implementation, one has just to reimplement the
following methods:
* root_dev_config()
* private_dev_config()
* volatile_dev_config()
- QubesVmStorage provides a default implementation of other_dev_config(),
because it can be shared by all storage implementations
The method XenStorage._format_disk_dev() generates the xml config for a device.
It is not specific to the Xen file storage implementation. It can and must be
reused by other storage implementations
We use only one device-mapper layer for HVMs, and this isn't the same as
for PV - it is that one, which PV does in initramfs.
Device-mapper layers summary for template-based VMs:
PV: root.img+root-cow.img (dom0) -> xvda, xvda+volatile.img (VM)
HVM: root.img+volatile.img (dom0)
Some VM types do not have particular disk image. Instead of enumerating
cases in storage class, signal unused image from VM class by setting
appropriate attr to None.
