Booting CentOS 5.5 in xen DomU

CentOS 5.5
kernel-xen0-*.*.rpm and kernel-xen-*.*.rpm are built with xenblk as a module, so that an attempt to boot into a DomU with the xen0 kernel dies with a message like:
mount: could not find filesystem '/dev/root'

sudo mkinitrd --with=xennet --preload=xenblk /boot/$KERNEL-$DOMNAME.img $KERNEL

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