While it may seem that zero detection is pointless for backing chain
layers other than the top one, which is usually the only one gettin
written to, with block operations such as active-layer commit the
non-top layer may become active, in which case the VM wouldn't be
configured in accordance to the XML any more.
Similarly with snapshots a new image is introduced which would not get
zero detection enabled, but next start of the VM would enable it.
Fix this by propagating the zero detection setting for all layers.
This problem partially addresses one of the issues reported in
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1120389
Fixes: 8a78f88a1a and a522c3044b (effectively reverts them)
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Andrea Bolognani <abologna@redhat.com>
Peter Krempa
475ed7075d