Re: [Xen-devel] Which OSes do NFSroot?

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> For Linux, that's ok, i know and use nfsroot capabilities of the kernel.
> But i was wondering about other OSes whose kernel don't support that
> option. I didn't look at XEN source code and am not sure i'd understand its
> principles if i read it!

The documentation means NFS root on guests that support it themselves.  There 
are other ways to access domain filesystems over the network, if desired.

>  From what I have understood, dom0 shares its device drivers with other
> guest OSes, right? If that's the case, then i guess one might NFS link
> to a distant OS image directory and then boot that OS NFSrooted, XEN
> "simulating a local disk".

You might, for instance, connect dom0 to a remote disk image using a network 
block device (ENBD, iSCSI, HyperSCSI...) and then export it to the guest as 
it's root filesystem.  Actual NFS isn't a particularly good fit here but 
those other protocols would be fine.

> Actually, i'm MUCH concerned about MS Windows XP. I know ther's no
> support currently  for licence issues, but everybody (web sources) say
> XEN 3.0 will enable running XP.

Xen 3.0 will enable running XP *on a machine with hardware virtualisation 
assists* (i.e. using upcoming hardware from Intel / AMD - not available yet).

> Do developpers think users will be to run XP NFSrooted? What about INT 13?

Again, the best fit would probably be to store the filesystem on a network 
block device and export it to the guest as an ordinary disk.

> As well, i'm pretty curious as to know how to load XP kernel, as
> NT/2000/XP boot process is much more different than unices'.
> In fact, i was wondering if XenoXP developpers were bootstraping from a
> partition image (with a MBR, a partition table, and a valid partition
> boot sector allowing the ntdetect.com/ntldr process) as SYSLinux's
> MemDisk does, or if the had some tricks to directly bootstrap
> ntoskrnl.exe/hal.dll. Then again, what about INT 13?

Support for running XP will use whole machine virtualisation enabled by 
hardware virtualisation extensions.  The tools will set up a virtual machine 
with a complete set of virtual hardware (instead of the paravirtual machine 
we run ported guests in).  Then, you'll kick that virtual machine into life 
and XP will boot thinking it's on real hardware.

> To sum up: do xen developpers think it'll be possible to run XP
> nfsrooted in release 3.x ?

Can it boot from its disk image stored on a network device, rather than 
locally: yes.  This won't let you do all the things you can with NFS (have 
multiple writers to the filesystem) but it enables network transparency 
(useful, e.g. for migration).  Again, I don't think NFS would be a good fit 
here.

> Regards and a big 'congrats' to all of Xen developpers

Cheers,
Mark

>
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