The usage in xen.spec is like this:
 %post tools
 %{fillup_only -n xencommons xencommons}

Do a fresh install, modify the key=value pairs as required, then upgrade the
package, the sysconfig file is broken and changes are lost:

rm /etc/sysconfig/xencommons
zypper in --oldpackage xen-tools-4.12.4_02-3.30.1
echo XENSTORETYPE=domain >> /etc/sysconfig/xencommons
echo XENSTORE_DOMAIN_SIZE=123 >> /etc/sysconfig/xencommons
zypper in --oldpackage xen-tools-4.12.4_04-3.33.1
diff -u /var/adm/fillup-templates/sysconfig.xencommons
/etc/sysconfig/xencommons

The resulting diff is huge. Basically fillup removed all comments, and also the
two added key=value lines.


Apparently each key=value must be enabled, even if value is empty.
In case key= is commented out, the entire block is handled as dead comment and
will be removed.