Ian Pratt, of the University of Cambridge in England and the leader of the Xen project, said there were a number of reasons for the delay in including Xen in the kernel. Primarily, Xen 3.0 had suffered from a bit of feature creep. Physical Address Extension (PAE) 32b support and Virtualization Technology, for example, were added very late in the cycle. "We were aiming for an end-of-summer release, but this now looks on target for December," Pratt said.
It didn't make much sense to start preparing patches for sending upstream until the Xen 3 guest API was close to being frozen, because there is a significant resource cost in maintaining multiple trees, he said.
"We hit this point a month or so back, and there's actually been a lot of activity since then," Pratt said. "We've done a first cut reorganization of our patch into the form that was agreed on at the last Xen summit, forward ported it to the head of Linus [Torvalds'] tree, and put out a call for help to Red Hat, SuSE, IBM, HP and all the other stakeholders to help us beat it into shape. It's great to see them stepping up and promising to commit some of their best guys to help."