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On 16.01.14 at 19:18, Wolfgang Rosenauer wrote: Am 16.01.2014 18:39, schrieb Charles Arnold: Perhaps a more general question to the list is what is a reasonable backward compatibility level that we should be setting in the openSUSE kernel so that our VMs can run on older hosts?

I would have an opinion but I have no idea what the implications are when compatibility is extended.

One rule of thumb could be to provide compatibility down to oldest maintained openSUSE release (at release time of a new distribution) at least. And when I say that I would expect this to include the Evergreen maintained versions. So that would mean that 13.1 would need to support running on a 11.4 host (as in my case). For 13.2 (if it will be released in plan at all) it's a bit of a conflict. 11.4 is maintained at least until July 2014 while 13.2 is planned around that time. So talking about the theory I would also wish 13.2 to run on 11.4 still. And obviously all openSUSE releases should still run on SLES11 (not sure which Xen version is in the latest service pack there).

In the end that would likely mean that we can't ever bump the compatibility level - quite possibly someone else will show up and need things to be compatible going even further backwards than what you ask for.

But all that is without any idea what that means technically about efforts and disadvantages of being compatible with older Xen releases.

It's not a lot of effort (it really just means to alter that one kernel setting). The disadvantage is that more compatibility code will remain in the kernel, making it bigger, slower, and I can't exclude that in some cases might alter behavior (the most prominent example for this is the page table handling quirks needed for compatibility with 3.0.2 and earlier).

Was there any policy up to now how that compatibility level was chosen? Because currently (if my reading of the kernel parameter is correct) 13.1 is only compatible to run on 12.3 hosts and no older ones. This limitation is quite narrow in my opinion.

So far the policy was to be compatible with the immediately preceding release, such that migrating hosts and guests can be done in any order. Jan -- To unsubscribe, e-mail: opensuse-virtual+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse-virtual+owner@opensuse.org