gistfile1.txt

activation-time import:

1. create a zvol for the disk image based on the `import/hash-name` of the
   image file in the store
2. qemu-img dd the data from the `.qcow2` to the zvol
3. snapshot zvol to `import/hash-name:import`
4. For each `import/*` see if their path is live, if not: delete the
   snapshot and zvol (via: `nix-store --query --roots /nix/store/hash-name`


run-time code:

pre-start: create the volume named `execute/hash-name` if it doesn't
           already exist
pre-start: roll-back `execute/hash-name` to the snapshot for
           `import/hash-name:import`
    start: execute qemu with the parameters like this:
    
<disk type='block' device='disk'>
  <driver name='qemu' type='raw' cache='none'/>
  <source dev='/dev/zd0'/>
  <target dev='vda' bus='virtio'/>
  <alias name='virtio-disk0'/>
  <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
</disk>