Re: [Xen-devel] [PATCH 5/5] tools/libxenctrl: use new xenforeignmemory API to seed grant table

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Aug 04, 2017 at 03:02:03PM +0200, Marek Marczykowski-Górecki wrote:
> On Fri, Aug 04, 2017 at 01:26:21PM +0100, Wei Liu wrote:
> > On Wed, Aug 02, 2017 at 10:59:49AM +0100, Paul Durrant wrote:
> > > A previous patch added support for priv-mapping guest resources directly
> > > (rather than having to foreign-map, which requires P2M modification for
> > > HVM guests).
> > > 
> > > This patch makes use of the new API to seed the guest grant table unless
> > > the underlying infrastructure (i.e. privcmd) doesn't support it, in which
> > > case the old scheme is used.
> > > 
> > 
> > The code mostly looks fine.
> > 
> > What's the benefit of doing this?
> 
> Also, I see changed signature of xc_dom_gnttab_seed (it got is_hvm
> parameter). Wei, what is the policy for backward incompatible libxc API
> changes?

libxc isn't stable, so functions might get deleted / updated at any
point.

Most libxc functions are quite simple and are quite "close" to the
hypervisor.

The non-trivial functions I know of are VMI related ones but I think
users in that area already have the right expectation.

An important user of unstable libxc APIs is QEMU. It probes for specific
functions in the configure script to handle compatibility issues.

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