Re: Proposal for init/kexec/hotplug format for Xen

[Anthony Liguori <aliguori@us.ibm.com>]

Harry Butterworth wrote:

>>We could begin work today on libxen-hcall and libxen-idc while we work 
>>out what the store is going to like and how the OF structure is going to 
>>work.  Thoughts?
>>    
>>
>
>The most difficult aspect of the inter-domain communication API to
>express from the point of view of forwards compatibility with a
>fault-tolerant implementation is that, in a fault-tolerant system with
>different levels of fault tolerance, some domains will come and go
>whilst others persist across failures.
>
>  
>
I'm not sure fault-tolerance has to be implemented at the IDC primative 
level.  That seems like something that's implemented at a slightly 
higher-level in the stack.

For instance, I'm not sure how to even think about what a fault-tolerant 
semaphore would be however I can certainly imagine being able to 
implement a fault-tolerant protocol that uses semaphores and shared memory.

I think fault-tolerant primatives can quite comfortably sit on top of 
lower-level primatives.  My initial reaction is that a fault-tolerant 
primative is going to have a fair bit of overhead.  I think the 
interface is going to be fairly different too.  I'm not sure you want to 
pay the price of transparent fault-tolerance in all circumstances.

It would probably be better to expect to implement a separate set of 
fault tolerant devices and just design the non-tolerant devices for 
maximum code-reuse.

Regards,
Anthony Liguori



-------------------------------------------------------
SF email is sponsored by - The IT Product Guide
Read honest & candid reviews on hundreds of IT Products from real users.
Discover which products truly live up to the hype. Start reading now.
http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click