Chris Wright wrote:
> * Jeremy Fitzhardinge (jeremy@xxxxxxxx) wrote:
>
>> Chris Wright wrote:
>>
>>> Consistently wrap paravirt ops callsites
>>> "ugh" - mingo
>>>
>> Had a thought. What if we do a kind of reverse/two-way module linkage?
>> Somehow compile each pv-op implementation like a module, and then link
>> the appropriate one in at boot time.
>>
>
> This is very similar to something Steve was chatting with me about
> this morning. The idea he was tossing around was something a bit like
> an initrd that a load_module analog could link up. In a sense, it's
> similar to the VMI ROM, with the exceptions that the ABI is just created
> by the compiler from a normal mutable kernel API and it's linkage with
> symbols available on both sides.
>
Yeah. It would have to happen a lot earlier than initrd. It would be
more like a multiboot kernel module or something.
>> Tricky parts: it would need two-way unresolved references between kernel
>> and module, and it would need to be able to run very early in the
>> kernel's life.
>>
>
> This is the tricky part, and where Steve and I left off.
>
Fortunately the linker code should be pretty easy to make
self-contained. It shouldn't need to do memory allocations or anything
complex like that, so I think its just a matter of grovelling around and
fixing up linkages.
> I suspect we could free the unused backends already.
We could; we just need to make sure they get their own section so
they're easily separable.
> It also has one
> negative side-effect, which is promoting external module code that links
> with the kernel. IOW, there's much less incentive to get code merged
> if it's just a matter of linking.
It wouldn't be something we'd promote by making it easy to bind
out-of-tree code to the interface. And it would still be a
kernel-version-specific ABI; no guarantees of stability.
J
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