[Libvir] Scability / performance fix for virDomainLookupByID

Attached is a patch to significantly increase scalability / performance of the xenDaemonLookupByID method. The current implementation would get a list of all domain names from XenD, and then iterate doing a HTTP GET on /xend/domain/[name] until the domain with match ID was found. THis had O(n) complexity, with the result that when running on a system with 20 actives domains, 'virsh list' would have O(n^2) complexity needing ~230 HTTP calls, giving a runtime of ~9 seconds. The patch is to make the code do a HTTP GET on /xend/domain/[id] which we just discovered is a valid URL to access. This makes the method call O(1), and 'virsh list' is now a saner O(n), and completes in ~1 second. While still not great performance, this is certainly much better. I think it ought to be possible to optimize the code still further so that XenD is avoided altogether for simple commands which can be fullfilled purely with data available from Hypervisor, but that will need further investigation. Please review the patch in case I missed any bugs / edge cases Regards, Dan. -- |=- Red Hat, Engineering, Emerging Technologies, Boston. +1 978 392 2496 -=| |=- Perl modules: http://search.cpan.org/~danberr/ -=| |=- Projects: http://freshmeat.net/~danielpb/ -=| |=- GnuPG: 7D3B9505 F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 -=|