Re: Oldest supported Xen version in upstream QEMU (Was: Re: [Minios-devel] [PATCH v2 0/15+5+5] Begin to disentangle libxenctrl and provide some stable libraries)

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

On Wed, 2015-09-23 at 10:21 -0400, Konrad Rzeszutek Wilk wrote:
> On Wed, Sep 23, 2015 at 04:17:05PM +0200, Juergen Gross wrote:
> > On 09/23/2015 04:09 PM, Konrad Rzeszutek Wilk wrote:
> > > On Wed, Sep 23, 2015 at 09:29:10AM +0100, Ian Campbell wrote:
> > > > On Tue, 2015-09-22 at 22:31 +0100, Stefano Stabellini wrote:
> > > > > The oldest Xen version I build-test for every pull request is Xen
> > > > > 4.0.0,
> > > > > I think it is very reasonable to remove anything older than that.
> > > > > I am OK with removing Xen 4.0.0 too, but I would like a warning
> > > > > to be
> > > > > sent ahead of time to qemu-devel to see if anybody complains.
> > > > 
> > > > There is not much point in removing <=3.4 support and keeping 4.0,
> > > > since
> > > > 4.0.0 was the last one which used a plain int as a handle, anything
> > > > older
> > > > than 4.0.0 is trivial if 4.0.0 is supported.
> > > > 
> > > > One approach I am considering in order to keep 4.0.0 support and
> > > > earlier
> > > > was to turn the "int fd" for <=4.0 into a pointer by having the
> > > > open
> > > > wrapper do malloc(sizeof int) and the using wrappers do
> > > > xc_foo(*handle).
> > > > 
> > > > This way all the different variants take pointers and we have less
> > > > hoops to
> > > > jump through to typedef everything in the correct way for each
> > > > variant.
> > > > 
> > > > If you would rather avoid doing that then I think dropping 4.0.0
> > > > support
> > > > would be the way to go and I'll send a mail to qemu-devel.
> > > 
> > > Perhaps to help in killing the 4.0.0 support - Linux pvops can't work
> > > with Xen 4.0.0 - sadly I don't recall the details but I think it was
> > > missing
> > > an hypercall.
> > 
> > Are you sure? On the Xen developer summit this year I asked a guy from
> 
> And I am incorrect (from http://wiki.xen.org/wiki/Dom0_Kernels_for_Xen):
> 
> 	"Q: I've seen mentions of 'pv_ops' and 'xenlinux' kernels. Which
> one
> 	should I choose?
> 
> 	Simple answer: pv_ops. Xen Project 4.0 switched to using Linux
> pv_ops
> 	based dom0 kernel as a default.."

This contracts your hypothesis, it says that Xen 4.0 is expected to work
with a pvops dom0 (or else we wouldn't have switched to it by default).

I think the cut off you are thinking of was a bit older, e.g. 3.4 or so.

> 
> > Amazon whether they are testing upstream pvops kernels on all Xen
> > versions they support, and he confirmed that. And they do support Xen
> > 4.0 and older.

NB they presumably care about domU only for this testing, whereas whatever
the incompatibility is it was to do with dom0 only, since domU interface
has been stable since 3.0.

Ian.