"Finally Mark Johnson submitted to xen-devel mailing
list patch for ZFS 24 support at Xen 4.0. Patch mentioned bellow
was successfully tested at Xen 4.0 Dom0 with pvops kernel 126.96.36.199
on top of Fedora 12 via modifying Michael's Young
xen-188.8.131.52.fc12.src.rpm and direct patching xen 4.0 official
tarball on Ubuntu Karmic Koala Server. Download from 
fsimage-zfs-24.patch . Then add it to /root/rpmbuild/SOURCES folder
created via install xen-4.0.0-0.7.fc12.src.rpm :-"