Use xz filter instead of plugin, but apply cow layer.

xz filter in readonly mode is broken!

diff --git a/2019-fosdem/3000-xz-compressed.term b/2019-fosdem/3000-xz-compressed.term
index ba43450..37d6fc0 100755 (executable)
--- a/2019-fosdem/3000-xz-compressed.term
+++ b/2019-fosdem/3000-xz-compressed.term
@@ -7,7 +7,7 @@ export title="XZ compressed image"
 
 # 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'