Re: ABI coupling to hypervisors via CONFIG_PARAVIRT

[Ingo Molnar <mingo@elte.hu>]

* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> So please
> 
>  - point out things that are badly done. [...]

the thing badly done is fundamental and it trumps any other small 
technological detail complaint i have, because it affects the 
development and maintainance model: to promise backwards compatibility 
to 4-5 different hypervisors, using separate ABIs for each. /One/ such 
ABI would be complex enough to maintain IMO.

( if there is no backwards compatibility promise then i have zero
  complaints: then paravirt_ops + the hypercall just becomes another API
  internal to Linux that we can improve at will. But that is not
  realistic: if we provide CONFIG_VMI today, people will expect to have
  CONFIG_VMI in the future too. )

as i said in the very, very first email about this topic: /one/ new ABI 
towards hypervisors should be introduced step by step, and via concensus 
across hypervisors. We should treat the hypercall ABI very similar to 
the system call ABI: the system call ABI is largely based on a concensus 
between applications.

[ i think apic_write() granularity is bad too - but that is a small
  technical issue, dwarved by the ABI issues that impact the development
  model IMO. ]

	Ingo