[Xen-users] Re: Xen-users Digest, Vol 2, Issue 20

[Tim Deegan <Tim.Deegan@xxxxxxxxxxxx>]

> They are really useful, I have a configuration
> with one host machine with 8 UML virtual machines
> inside, all of them using only one root partition
> image, each of them having their exclusive cow file.
> 
> Yet, I do not know how to use them from Xen. If you
> are interested, go ahead and ask.

The "cow:" stuff on the demo CD is a bunch of scripts written
specifically for the CD that make copy-on-write snapshots of filesystem
images on the CD.  This is both so that we can boot more than one domain
from the same image, and so that we don't have to worry about the
filesystem's not being writeable.

If you're interested in how they work, have a look at /sbin/snapshot.sh
and /sbin/unsnapshot.sh to see the dmsetup commands used, and in
/etc/xen/scripts/ to see how to extend the xm disk description syntax.
/sbin/cow_root.sh is the script used in the ramdisk to set up the first
copy-on-write device for domain 0.

Tim.

-- 
Tim Deegan                           (My opinions, not the University's)
Systems Research Group
University of Cambridge Computer Laboratory

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