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Re: [Xen-devel] [libvirt] [PATCH-RFC] Change libxl to use Xen 4.2 interface

On Thu, May 10, 2012 at 10:56:06AM +0100, Ian Campbell wrote:
> On Wed, 2012-05-09 at 18:13 +0100, Daniel De Graaf wrote:
> > This patch changes libxl to use the interface in Xen 4.2. It is provided
> > as an example, not intended to go in to libvirt as-is since it removes
> > all support for libxl from Xen 4.1. It also still has some cruft (extra
> > void casts on parameters) and the device model info population is not
> > written. It has been tested with simple domain create/destroy.
> > ---
> >  src/libxl/libxl_conf.c   |  134 +++++++++------
> >  src/libxl/libxl_conf.h   |    8 +-
> >  src/libxl/libxl_driver.c |  430 
> > ++++++++++++++++++++++++++--------------------
> >  3 files changed, 326 insertions(+), 246 deletions(-)
> Thanks Daniel, interesting to see. It doesn't seem as invasive as I
> expected given the number of changes to libxl's interfaces between 4.1
> and 4.2. 
> I suppose it is worth mentioning in this context that we are intending
> to maintain the 4.2 libxl API in a stable manner going forward, as
> described near the top of:
> http://xenbits.xen.org/hg/staging/xen-unstable.hg/file/tip/tools/libxl/libxl.h
> Since libvirt is one of the main reasons we are doing this it would be
> useful to check that this actually meets the needs from that side.

Having a long term stable API for libxl certainly gets our vote.

WRT the use of LIBXL_API_VERSION to control API version. Libvirt generally
aims to support all possible API versions, so I expect we would not want
to define LIBXL_API_VERSION. Instead the libvirt code would #ifdef various
bits according to the libxl version it detects.

> That doesn't really help with support 4.1 and 4.2+. A large portion of
> the below looks like it would be reasonably easy to abstract away with a
> header full of compat defines for naming changes etc, other bits don't
> look so simple to deal with.

Personally I would prefer to keep support for all 4.x versions, but I'll
defer to Suse developers to decide upon this since they are the primary
maintainers & users of the libxl driver.

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