Xen was expected to be built tightly into the Linux kernel at the heart of the open-source operating system. But Andrew Morton, a key deputy to Linux leader Linus Torvalds, is advocating an interface in the Linux kernel that would let it work with any virtualization foundation.

Virtualization generally refers to software and hardware that let a single computer run multiple operating systems. It is useful for making servers more efficient and isolating desktop applications into noninterfering partitions called virtual machines. Xen, Microsoft and VMware all are working on software called a "hypervisor" that governs how those virtual machines get access to the hardware resources.

Morton said he prefers a neutral interface that works with any hypervisor, rather than the Xen-specific patch to Linux that had been envisioned.

"For a long time, it was thought that we'd just merge the Xen patches as-is and be happy. But then, Linux would only run on Xen," Morton said. Instead, VMware programmers suggested a documented, stable interface between the kernel and the hypervisor--and they're preparing one, he said.

"From a high-level design perspective, I think that VMware's point is a good one, and that a general kernel-to-virtual machine interface is a better thing than a Xen-only one," Morton said.

XenSource and VMware both are fine with the change, but VMware gets a place at the table it lacked before.