RE: [Xen-devel] TCP state between domU and client

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> pradeep singh rautela
> Sent: 24 April 2007 13:43
> To: xen-devel
> Subject: [Xen-devel] TCP state between domU and client
> 
> Hi All,
> 
> I have a query.
> How is a TCP connection state maintained across domUs and a 
> remote client? 
> Any pointers to the code will be really helpful.

This is ABSOLUTELY the same as if you have a connection between a
"bare-metal" machine, it's handled in the TCP-layer which is unchanged
between Xen and native Linux. If you don't understand how that works,
then you probably need to look at documentation of how the Linux
TCP-stack works. For the TCP-layer, there's no need to understand if a
machine is a real physical machine or a virtual machine. 
> 
> Second question ,Can I run a Xen hypervisor inside a domU, 
> making this domU as the host and subsequent domUs  as guests 
> running over this guest domU ? Just asking this out of curiosity. 

Yes, no, maybe. You can (so I've been told, I haven't tried) run
Xenified Linux on top of a HVM DomU. Obviously, any guest on top of that
would not be able to use the HVM feature, as that is a "single-layer". 

But for para-virtual domains, you can't run the hypervisor on top of
itself, because the hypervisor needs Ring0 (the most privileged
protection level). Any subsequent load would fail to control this level,
so it's not possible to run the hypervisor at this level. 

It is also pretty pointless (aside from the fun and games you can have
with it, and I guess it's proving a point, in the same way as compiling
the source for the compiler with itself proves that the compiler is
working pretty well [This can also be more useful, as the compiler is
perhaps able to do optimization that isn't available in the previous
compiler]). 

--
Mats
> 
> Thank you 
> 
> ~psr
> 
> 
> -- 
> ---
> pradeep singh rautela
> 
> "Genius is 1% inspiration, and 99% perspiration" - not me :) 
> 



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