[lkml]   [2007]   [Mar]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: ABI coupling to hypervisors via CONFIG_PARAVIRT

* Chris Wright <> wrote:

> * Ingo Molnar ( wrote:
> > ( 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. )
> This was the whole reason we didn't adopt VMI directly. Instead,
> preferring an kernel internal API, pv_ops, that can adopt naturally as
> the kernel changes, and it is the pv_ops client code's (or backend as
> it is also referred to) responsibility to do whatever is necessary to
> map back to the hypervisor's ABI. The goal was explicitly to keep
> things internal fluid as usual. As I said before, no matter how you
> slice it there's glue code somewhere to deal with compatibilities. And
> it's always been the virtualization platform's responsibility to deal
> with the changes.

For example, for the sake of argument, if the VMI ABI consisted only of
a single call:

#define VMI_CALL_NOP 1

then obviously it would be very hard for VMI to adopt to changes in the
kernel - no matter how many smarts you put into paravirt_ops :-)

agreed? That is the center of my argument. Does the VMI ABI limit the
Linux kernel or not?

As we increase the complexity of a hypercall ABI, more and more things
can be implemented via it. So _obviously_ there is a 'minimum level of
capability' for every hypercall ABI that is /required/ to keep the Linux
kernel 100% flexible. If in some tricky corner the ABI has some stupid
limit or assumption, it might stiffle future changes in Linux.

i am worried whether /any/ future change to the upstream kernel's design
can be adopted via paravirt_ops, via the current VMI ABI. And by /any/ i
mean truly any. And whether that can be done is not a function of the
flexibility of paravirt_ops, it's a function of the flexibility of the

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2007-03-09 22:51    [W:0.559 / U:0.012 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site