Re: RFC: "local" communications

[Nivedita Singhvi <niv@us.ibm.com>]

Anthony Liguori wrote:
> Rik van Riel wrote:
> 
>> Hi,
>>
>> When combining clustering with cluster storage, the situation
>> arises where virtual machines are not only managed by the cluster
>> software, but also need to participate in the cluster software
>> themselves...
>>
>> In order for this to work better, it would be good if there
>> was a way for software in a domU to communicate with software
>> on the local dom0 - so after being migrated elsewhere, a guest
>> would start talking to the new dom0 automatically.

Rik, is this a heartbeat kind of protocol or some such thing?
Is there value to making it be a generic solution that would
work when communicating in a non-xen environment?

>> Should it be some virtual device analogous to the virtual
>> network driver, or should we have some other kind of socket
>> for node local communications ?

Using protocols like TCP for node-local comms is undesirable
as TCP is engineered for the heavy machinery of the Internet.
UDP or raw sockets will be somewhat better, although AF_UNIX
would be best of all (albeit with its own constraints).

>> What kind of approach would the Xen community (that's you, if
>> you read this far) prefer ?
>>  
>>
> I can only speak for myself, but I'd personally like to see a small 
> userspace library that established a datagram connection between two 
> domains (using an event channel and a shared page) that could be reused 
> for many applications.

Which datagram service, Anthony?  Having a small lib like this
would be a good idea, although the benefit would be in the details,
and of course, depending on how many apps we need to support that
we don't want to modify...

> If it could be used with normal read/write calls that would be even 
> better (although first thought is that that would require a daemon).

Probably don't want to do that...

thanks,
Nivedita