Linux 3.0 Will Have Full Xen Support

GPLHost-Thomas writes "The very last components that were needed to run Xen as a dom0 have finally reached kernel.org. The Xen block backend was one major feature missing from 2.6.39 dom0 support, and it's now included. Posts on the Xen blog, at Oracle and at Citrix celebrate this achievement."

Comments

Meanwhile

[TheRaven64]

Xen Dom0 support has been supported in released versions of NetBSD and Solaris for something like 4 years, while the VMWare lobby on the LKML was requiring the entire paravirtualisation subsystem to be rewritten before they'd accept patches, and Red Hat decided to push KVM as a Xen replacement, in spite of them having very different capabilities.

Re:I hopefully speak for lots of people when I say

[martyros]

But doesn't that just make Xen the OS with linux becoming an application? I mean, it is the OS's job to manage memory and devices, and to allocate CPU time.

No, Xen is a hypervisor. A process expects a *lot* more from an operating system than an OS expects from a hypervisor. VMs expect raw hardware and know they have to manage most things (like setting up memory, doing filesystems, and so on) themselves. Processes expect an operating system set up memory mapping for them, give them filesystems (not just raw disks), IP addresses and sockets and TCP (not just raw packets), and so on.

In the KVM case, Linux is an operating system to normal processes, but a hypervisor to VMs. Linux gives memory and time to the guest OS, and the guest OS gives memory and time (along with filesystems, TCP, &c) to guest processes. So in that way Xen and KVM (i.e., Linux-as-hypervisor) are the same.

The main difference is that Xen is only a hypervisor, whereas with KVM, Linux tries to be both a hypervisor and an operating system. That has a number of practical implications. Xen has been widely deployed and tested as an enterprise-class hypervisor. I'm not aware of any large-scale enterprise deployments of KVM, so it remains to be seen whether Linux can successfully be both an enterprise-class hypervisor and an operating system at the same time.