Hi, nice tool, thanks a lot

tried it in Ubuntu 20.04.2 LTS

1. apparmor issues - libvirtd not allowed to create sockets in /var/tmp

2021-04-20 17:38:50 INFO common - printVersion: Version: 0.17 Arguments: /usr/local/bin/virtnbdbackup -d vm-template -l full -o /mnt/backup/vm-template
2021-04-20 17:38:50 INFO virtnbdbackup - main: Domain has 1 disks attached which support changed block tracking.
2021-04-20 17:38:50 INFO virtnbdbackup - main: Looking for checkpoints
2021-04-20 17:38:50 INFO virtnbdbackup - main: Using checkpoint name: virtnbdbackup
2021-04-20 17:38:50 INFO virtnbdbackup - main: Temporary scratch file target directory: /var/tmp
2021-04-20 17:38:50 INFO virtnbdbackup - main: Starting backup job.
2021-04-20 17:38:50 WARNING libvirthelper - startBackup: Guest agent is not responding: QEMU guest agent is not connected
2021-04-20 17:38:50 ERROR virtnbdbackup - main: internal error: unable to execute QEMU command 'nbd-server-start': Failed to bind socket to /var/tmp/virtnbdbackup.868194: Permission denied

obvious workaround is to disable apparmor

extenthandler.py:
def _setRequestAligment(self):
align = self._nbdFh.get_block_size(0)
if align == 0:
align = self._align
return self._maxRequestBlock - align + 1

Ubuntu has libnbd 1.2.2 with missing get_block_size()
is it safe to skip get_block_size() and use self._align if no get_block_size() available ?