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Paravirtualized driver competition benefits Linux users

What's the deal with Novell, Microsoft and Red Hat licensing paravirtualized drivers? Will they all be GPLed? How will Linux users benefit from paravirtualized drivers?

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Are you referring to the SUSE Linux Enterprise Virtual Machine Driver Pack that contains paravirtualized drivers for Red Hat Enterprise Linux, Microsoft Windows and SUSE Enterprise Linux? The Red Hat and SUSE drivers in it are "distributed under an open source license," according to Novell, while the Microsoft drivers are proprietary (60-day free trial after downloading). Novell's drivers presumably gain the advantage of Microsoft source code availability for their development.

Red Hat's own paravirtualized drivers for Microsoft will be based on open sources where available; in the case of proprietary material like Microsoft, Red Hat must reverse engineer the drivers without a knowledge of the underlying code. In any case the Red Hat drivers will be Open Source, and the company sees no need to negotiate a license with Microsoft in order to write them.

Both Red Hat and Novell are using Xen for virtualization. Interestingly, Microsoft was an early contributor to the Xen project. Microsoft offers both a < a target="_blank" href="http://www.microsoft.com/windowsserversystem/virtualserver/default.aspx">Virtual Server and a Virtual PC. Their paravirtualized drivers are both included and both proprietary.

The advantages of paravirtualization come from its use of a layer between the guest and host operating systems called the virtual machine monitor, or hypervisor. This layer directs hardware calls from the guest operating systems down to the host operating system. By depending on the host system for hardware drivers, their (slow) emulation in the virtual system is eliminated. The increase in operational speed is significant, but is paid for by difficulty of development in I/O, memory, privilege rings and memory management. Also, the guest operating system must be modified before it can be run on host system.

Currently, Xen works by paravirtualization, and is built into the Linux kernel; KVM (the Kernel-based Virtual Machine, likewise built into the kernel) is currently adding paravirtualization to its present technology.

The current gold rush in virtualization and paravirtualization will enable Linux users to run atop Windows or to run Windows on Linux. Currently we can do this, but the new technologies will enable more machines to be run as guests. The competition among the different systems (and their convergence), and the fact that the kernel supports both KVM and Xen seem to offer hope that the best of the competition will benefit Linux users.

This was first published in February 2008

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