Domain suspend mechanism

[James Rhett Aultman <jaultman@cise.ufl.edu>]

Xen Developers:

My name is Rhett Aultman, and I'm a Ph.D student at the University of
Florida.  I'm taking a class which studies virtual machines, and I'm
using Xen for my term project.  Specifically, I'm attempting to
implement a "wake on LAN" feature in Xen, whereby a domain can be
suspended and later restarted if a network packet arrives and would be
delivered to the domain had it been running.

At the moment, I'm trying to understand how the domain suspension
mechanism works.  I am fairly sure the codebase I'm using is a recent
copy of Xen 3.0 unstable, if that helps.  I've found that most of the
process of saving a domain to an image file is in the libxc library
function called xc_linux_save( ) or something similar, but the actual
events going on during suspension do not yet make sense to me.  It seems
there's a utility function called suspend_and_state( ), and it seems to
suspend a target domain...but the only way it seems to do so is by
sending the string "suspend" via standard out.  How this works, and how
the target domain receives the message, I do not understand.

Additionally, if anyone here has any advice or opinions on how a "wake
on LAN" feature might be implemented, I'm all ears.  I've noted that the
Xen hypervisor doesn't manage much of the mechanics of a domain's saving
and restoration, so the process of bubbling up the information that a
packet has arrived for a suspended domain will be...interesting.  I'm a
total rookie with your codebase, so any advice you could provide would
help me.

--
Rhett.