[Xen-devel] PV drivers for HVM guests

["Ky Srinivasan" <ksrinivasan@xxxxxxxxxx>]

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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