xz filter in readonly mode is broken!
# History.
remember 'ls -lh Fedora-Cloud-Base-29-1.2.x86_64.raw.xz'
# History.
remember 'ls -lh Fedora-Cloud-Base-29-1.2.x86_64.raw.xz'
-remember 'nbdkit xz Fedora-Cloud-Base-29-1.2.x86_64.raw.xz'
+remember 'nbdkit --filter=cow --filter=xz file Fedora-Cloud-Base-29-1.2.x86_64.raw.xz'
remember 'ps ax | grep nbdkit'
remember 'sudo nbd-client -b 512 localhost /dev/nbd0'
remember 'sudo mount /dev/nbd0p1 /tmp/mnt'
remember 'ps ax | grep nbdkit'
remember 'sudo nbd-client -b 512 localhost /dev/nbd0'
remember 'sudo mount /dev/nbd0p1 /tmp/mnt'