Re: Xen newbie: inter-domain communication

[Derrik Pates <dpates@dsdk12.net>]

Chotu Ram wrote:
> 1. As far as I can understand (and I might be wrong) Xen maintains two 
> domains dom0 (control domain) and dom1 (the other guest OSes). When the 
> documentation says inter-domain communication, is it only referring to 
> the communication between the dom0 and dom1, or it can also be applied 
> to the communication among the guest OSes (unprivileged that is).

A "domain" is a single virtual execution space, more or less. Each 
"virtual machine" is a separate domain. (When you do "xm list", the "Id" 
field is the "domain ID".) So yes, an inter-domain commmunication 
channel can exist between domain 0 and any other domain (running virtual 
machine).

> 2. What are the capabilities of the inter-domain communication method. 
> Specifically: what protocol is used to communicate?, what kind of 
> information can be communicated? Can this communication be used for 
> logging/auditing? Does anybody has any experience using this method or 
> has any working example?

As I understand, the "protocol" is basically just a per-channel 
"interrupt" (to get the other side's attention as needed), and a shared 
page, which is exchanged between the two domains as needed (only one can 
be interacting with it at a time, I think). The virtual block device 
driver and virtual network interface driver, as I understand it, 
structure it as a big ring buffer, and encode messages (and assign pages 
of their allocated memory to the other side of the channel for a 
DMA-like exchange method) in that ring buffer. Look at the developer 
documentation for a better explanation.

-- 
Derrik Pates
dpates@dsdk12.net


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