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Re: [Xen-devel] PV drivers for HVM guests

Interesting!  Ideally, there would be better performance in the base HVM
device model.  I think I know of some people that are working hard on

I'm curious to see what you've done for (1) and (2).


On Tue, 2006-10-03 at 16:31 -0400, Ky Srinivasan wrote:
> I am trying to build PV drivers for SLES9 HVM guests. SLES 9 is based on the 
> 2.6.5 kernel. Since the PV driver code is really designed for the latest 
> kernel release, I have had many issues/problems in building the PV drivers 
> for older Linux OS targets - I have only been looking at the issues with 
> 2.6.5 kernel base and I suspect the problem will be even worse if one were to 
> look at older Linux kernels. This is unfortunate since PV drivers are so 
> critical for HVM guests and there is considerable interest in supporting 
> legacy Linux environments as HVM guests. The problems I have had to deal with 
> can be broadly classified into:
> a) Compiler related issues
> b) Missing functionality in the legacy kernel - this includes features as 
> well as changed data structures
> c) Implementation differences of a given feature
> These differences can be dealt with in a couple of different ways:
> 1) Modify the code in the PV drivers under appropriate compilation switches 
> to deal with the differences in the base kernels.
> 2)  Introduce  a compatibility component that bridges the gap between the 
> current PV code and a given Linux target and leave much of the PV driver  
> code untouched.
> I have implemented both these schemes for the sles9 kernel and would like to 
> get your input on your preference. I personally like option 2. Going forward, 
> the evolution of PV drivers needs to be constrained by the required support 
> for legacy Linux environments. 
> Regards,
> K. Y. Srinivasan 
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