Re: [Xen-devel] Proposal for init/kexec/hotplug format for Xen

[Anthony Liguori <aliguori@xxxxxxxxxx>]

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



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