I thought that one of the main blockers was that RedHat wanted to be able to keep binary compatibility for kernel modules, so that any module built for a kernel in a particular RHEL version would work with any kernel of the same series. Note that I say "wanted" - I doubt it works perfectly in practice and may be wrong altogether.
Posted Mar 15, 2012 16:27 UTC (Thu) by pbonzini (subscriber, #60935)
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It works as long as the module sticks to the defined set of symbols which make up the RHEL kernel stable ABI. RHEL kernel backports usually are also very cautious in changing the meaning of enums and other stuff like that.