Re: [Minios-devel] [PATCH v4 0/<VARIOUS>] Begin to disentangle libxenctrl and provide some stable libraries

[Ian Campbell <ian.campbell@citrix.com>]

On Thu, 2015-11-19 at 16:20 +0000, Stefano Stabellini wrote:

(Backing up this thread a bit).

> > It seems like much of this would be candidates for adding to
> > libxendevicemodel, but the underlying unstable interfaces pose a problem
> > there. I'm going to leave this for another day.
> 
> Does the Xen<->libxc interface need to be stable for libxendevicemodel
> to have a stable ABI?
> I think that libxendevicemodel could be stable, no matter what hypercall
> is eventually called underneath. Am I missing something?

I remember this morning why this matters, it's not the user space library
ABI etc, but rather that if we want libxendevicemodel to be able to lock
its fd to a specific domain (which we eventually do) then the kernel driver
needs to be able to introspect the privcmd hypercalls[0] so the underlying
hypercall does really need to be stable (since we don't want to be
constantly reving the kernel driver when something changes).

Given a stable hypercall interface underneath given the wrapping library a
stable ABI is a no brainer.

Ian.

[0] or to provide a dedicate ioctl or something, either way it is the
kernel which needs to be providing the lockdown functionality.