[Xen-devel] Re: Domain Save-Restore

[Chotu Ram <chotwo@xxxxxxxxxxx>]

Mark Williamson <maw48 <at> cl.cam.ac.uk> writes:

> > I would like to understand the method used by Xen to Save/Restore domains.
> > As far as I tried... most of the code is written in python and exists in
> > lib/python/xen/sv/ directory. I am not much familier with python, but this
> 
> * SV is the (experimental) web interface and is located in 
> tools/python/xen/sv/.
> * Xend is the control daemon and handles all sorts of control-plane things 
> including receiving commands from SV and the xm command line tool and 
> dispatching them to the rest of the system.  Xend lives in 
> tools/python/xen/xend/.
> * Xfrd is the migration / suspend daemon and is written in C for performance 
> reasons.  It accepts commands dispatched from Xend itself.  It lives in 
> tools/xfrd/ and contains the actual code for suspending / migrating a domain.
> 
> HTH,
> Mark

Hi Mark,

Thanks for that info.

I would like to know if it makes any sense to be able to figure out the process
table information from the saved image of the VM. I am still not too sure about
the save operation, but feel that it is more or less a memory dump. If that is
the case, then hypervisor would copy the image back ad somehow restart the VM.
Could you enlighten me about how does the hypervisor advises (or triggers) the
VM so that its running... how are the registers saved and restored. I know these
questions might seem little novice but I am still learning Xen and not sure
about the structure of the code. Also, is there any official documentation
available for the code structure (apart from the interface manual).

How do you put the VM into pause domain? and whats the advantage of putting it
in pause? does it freeze all the processes and restricts the CPU cycles alloted
to it? If that is the case, is there a way to be able to read this frozen state
information using hypervisor.

I would really appreciate any help in this regard.

Chotu



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