Re: [libvirt] Fixing libvirt's libxl driver breakage -- where to define LIBXL_API_VERSION?

["Daniel P. Berrange" <berrange@redhat.com>]

On Mon, Jun 27, 2016 at 04:54:35PM +0100, Ian Jackson wrote:
> (Adding Jan Beulich)
> 
> Ian Jackson writes ("Re: [libvirt] [Xen-devel] Fixing libvirt's libxl driver breakage -- where to define LIBXL_API_VERSION?"):
> > It seems that the libvirt LIBXL_API_VERSION is now rather higher, at
> > 0x040400, since libvirt#fccf27253ced
> >   libxl: switch to using libxl_domain_create_restore from v4.4 API
> > 
> > One unfortunate effect of this is to break the osstest tests of the
> > Xen 4.3 stable branch, which for the moment is still allegedly in
> > security support.
> > 
> > I can't really see a way that this kind of problem could be avoided
> > in principle, without
> >   - providing a more sophisticated way for libxl callers to set the
> >     requested version
> >   - providing more compatibility code in libvirt, too, and retaining
> >     it for some time
> > 
> > I think instead that it would probably be better for osstest to
> > "freeze" the version of libvirt that it is using, every time we branch
> > Xen.
> > 
> > So Xen 4.4 would be tested with whatever libvirt we were using when
> > the stable branch for Xen 4.4 was made, and so on.
> > 
> > Does that sound sensible ?
> 
> In the assumption that it is, I have:
> 
> Created the following branch refs on xenbits in the toplevel
> libvirt.git:
> 
>  osstest/frozen/xen-4.3-testing 9a0c7f5f834185db9017c34aabc03ad99cf37bed
>  osstest/frozen/xen-4.4-testing 33fb8ff185846a7b4974105d2c9400690a6f95cf
>  osstest/frozen/xen-4.5-testing cda1cc170f07b45911b3dad03e42c8ebfc210fa1
>  osstest/frozen/xen-4.6-testing eac167e2610d3e59b32f7ec7ba78cbc8c420a425
>  osstest/frozen/xen-4.7-testing 1a41ed5af5e1704dd9b0bdca40df5c9cacbdabfc

How did you pick those hashes ? Would it make more sense to pick the
nearest libvirt release tag ? eg v1.3.2 instead of 33fb8ff18584 ?

> 
> These were those tested by the following `tolerable' osstest push gate
> flights for the corresponding Xen tree:
> 
>  xen-4.3-testing 9a0c7f5f8341 86673
>  xen-4.4-testing 33fb8ff18584 85031
>  xen-4.5-testing cda1cc170f07 83135
>  xen-4.6-testing eac167e2610d 96031
>  xen-4.7-testing 1a41ed5af5e1 95728
> 
> And I have prepared the patch below, which (together with a
> prerequisite, in my tree) will implement this in osstest.
> 
> Ian.
> 
> From 5d1c91d3c53b580305e96d62f8ca84f85f8d3011 Mon Sep 17 00:00:00 2001
> From: Ian Jackson <ian.jackson@eu.citrix.com>
> Date: Mon, 27 Jun 2016 16:49:52 +0100
> Subject: [OSSTEST PATCH] cr-daily-branch: libvirt: use frozen version on
>  stable branches
> 
> libvirt master might increase its LIBXL_API_VERSION.  When this feeds
> through osstest it can cause the push gates of Xen stable branches to
> break.
> 
> So for stable Xen branches do not track libvirt upstream.  Instead,
> use a frozen revision.  (Only for main push gate tests of stable Xen
> branches.)
> 
> The frozen branch is never going to be updated so it is not suitable
> for other kinds of uses.  In particular it won't get security fixes.
> So we call the refs   osstest/frozen/xen-K.L-testing  to discourage
> users from using them.
> 
> Deployment note: The Xen release checklist needs a new item "add this
> frozen libvirt branch".
> 
> Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
> ---
>  cr-daily-branch | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/cr-daily-branch b/cr-daily-branch
> index 8b7c789..21780b8 100755
> --- a/cr-daily-branch
> +++ b/cr-daily-branch
> @@ -186,6 +186,12 @@ if [ "x$REVISION_OVMF" = x ]; then
>      fi
>  fi
>  if [ "x$REVISION_LIBVIRT" = x ]; then
> +	case "$xenbranch" in
> +	xen-[0-9]*-testing)
> +		BASE_TAG_LIBVIRT=osstest/frozen/$xenbranch
> +		export BASE_TAG_LIBVIRT
> +		;;
> +	esac
>  	determine_version REVISION_LIBVIRT libvirt LIBVIRT
>  	export REVISION_LIBVIRT
>  fi

Overall I think your approach makes sense.

Regards,
Daniel
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