This prevents simultaneous attachment of the same device (in practice)
to multiple VMs.
This change to be effective requires udev action being called when such
device is attached/detached to some domain. Script
/etc/xen/scripts/block will take care of it.
FixesQubesOS/qubes-issues#1081
Exclude exclude device if mounted/part of other device, or any of its
partition is used (same definition). Update this state whenever device
or it's partition receives udev event.
FixesQubesOS/qubes-issues#1600
When device becomes non-attachable (for example because it gets mounted,
or used as part of LVM/RAID/whatever), it should be removed from
advertised available devices. The code for removing QubesDB entry was
buggy - the device is actually a directory in QubesDB, not a single
entry.
QubesOS/qubes-issues#1600
