While Microsoft's submission Monday of driver source code to the Linux kernel is monumental on its face, under the covers it leaves a few unanswered questions about virtualization.

"This submission is goodness, but the question now is how much goodness," said Chris Wolf, an analyst with the Burton Group.

On Monday, Microsoft submitted source code for inclusion in the Linux kernel under a GPLv2 license.

The code consists of four drivers that are part of a Microsoft technology called Linux Device Driver for Virtualization. The drivers, once added to the Linux kernel, will provide the hooks for any distribution of Linux to run on Windows Server 2008 and its Hyper-V hypervisor technology.

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One of the drivers is a virtual hypervisor bus that talks to the Windows Hyper-V platform that will sit underneath Linux. The other three are positioned on top of that and address performance and storage. One is for virtual networks, one for virtual SCSI and the last is virtual block, a storage mechanism similar to SCSI.

Wolf said there are a few things the virtualization user base is going to want to know, such as whether users will see similar driver compatibility that exists between Microsoft and Citrix today.

"I can install power virtualized drivers on Xen server and they include the driver libraries for Hyper-V so that if I move a Xen server virtual machine to Hyper-V I can just run it without any modification. I am hopeful that with these open source drivers I will have similar compatibility between Hyper-V, Xen and KVM. That would be ideal," he said.

KVM is the hypervisor technology that is already a part of the Linux kernel.

Wolf said one other pressing question is how fast Novell and Red Hat will backport the new Microsoft virtualization drivers to their distributions.

Greg Kroah-Hartman, the Linux driver project lead and a Novell fellow, said Novell won't hesitate.

"We will have to backport the driver to our enterprise kernel, and that will happen quickly. One of our requirements to get code into our kernel is that it must be accepted upstream and it is now accepted upstream and we can backport it. I don't know a delivery date," he said.

Microsoft's open source driver technology will first appear in December as part of the 2.6.32 release of the kernel.

Wolf said another issue will be performance, specifically around the fact that Microsoft's Hyper-V support for Linux guest operating systems allows only for a single virtual CPU.

"For some applications that run on Linux that is not going to be enough compute power," he said. "Microsoft would need to increase its support to multiple CPUs for Linux guests."

Wolf said that while the issues are more of a platform, support and certification matter it is still an important point of clarity in grading out Microsoft's driver submission to the Linux kernel.

"Microsoft needs this if they are going to be a serious platform for Linux guests," he said.

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This story, "Microsoft's Linux kernel submission raises virtualization questions" was originally published by Network World .