Previously, upgrading a fully virtualized guest system from Red Hat Enterprise Linux 4.6 (with the kmod-xenpv package installed) to newer versions of Red Hat Enterprise Linux 4 resulted in an improper module dependency between the built-in kernel modules: xen-vbd.ko & xen-vnif.ko and the older xen-platform-pci.ko module. Consequently, file systems mounted via the xen-vbd.ko block driver, and guest networking using the xen-vnif.ko network driver would fail.
In Red Hat Enterprise Linux 4.7, the functionality in the xen-platform-pci.ko module was built-in to the kernel. However, when a formally loadable kernel module becomes a part of the kernel, the symbol dependency check for existing loadable modules is not accounted for in the module-init-tools correctly. With this update, the xen-platform-pci.ko functionality has been removed from the built-in kernel and placed back into a loadable module, now allowing the module-init-tools to check and create the proper dependencies during a kernel upgrade.