Re: [Xen-devel] [PATCH raisin 4/4] Update to 4.7, update qemu and qemu_traditional recipes

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Tue, Jun 14, 2016 at 11:34:43AM +0100, George Dunlap wrote:
> On 14/06/16 11:31, Stefano Stabellini wrote:
> > On Tue, 14 Jun 2016, George Dunlap wrote:
> >> On 14/06/16 11:08, Stefano Stabellini wrote:
> >>> On Tue, 14 Jun 2016, George Dunlap wrote:
> >>>> On 14/06/16 10:46, Stefano Stabellini wrote:
> >>>>> On Mon, 13 Jun 2016, George Dunlap wrote:
> >>>>>> Add a 4.7 config file, make it the default.
> >>>>>>
> >>>>>> Also update the qemu and qemu_traditional recipies after Ian Cambell's
> >>>>>> work to split off separate libraries.
> >>>>>>
> >>>>>> Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxx>
> >>>>>> ---
> >>>>>> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> >>>>>> ---
> >>>>>>  components/qemu             | 21 +++++++++++++--------
> >>>>>>  components/qemu_traditional |  2 +-
> >>>>>>  configs/config-4.7          |  8 ++++++++
> >>>>>>  defconfig                   |  2 +-
> >>>>>>  4 files changed, 23 insertions(+), 10 deletions(-)
> >>>>>>
> >>>>>> diff --git a/components/qemu b/components/qemu
> >>>>>> index e0d92a5..8624b50 100644
> >>>>>> --- a/components/qemu
> >>>>>> +++ b/components/qemu
> >>>>>> @@ -23,15 +23,20 @@ function qemu_build() {
> >>>>>>      cd "$BASEDIR"
> >>>>>>      git-checkout $QEMU_URL $QEMU_REVISION qemu-dir
> >>>>>>      cd qemu-dir
> >>>>>> -    ./configure --enable-xen --target-list=i386-softmmu 
> >>>>>> --prefix=$PREFIX \
> >>>>>> -        --extra-cflags="-I$INST_DIR/$PREFIX/include" \
> >>>>>> -        --extra-ldflags="-L$INST_DIR/$PREFIX/lib 
> >>>>>> -Wl,-rpath-link=$INST_DIR/$PREFIX/lib \
> >>>>>> +
> >>>>>> +    ./configure --enable-xen --target-list=i386-softmmu \
> >>>>>> +              --prefix=$PREFIX \
> >>>>>> +              --extra-cflags="-DXC_WANT_COMPAT_EVTCHN_API=1 \
> >>>>>> +              -DXC_WANT_COMPAT_GNTTAB_API=1 \
> >>>>>> +              -DXC_WANT_COMPAT_MAP_FOREIGN_API=1 \
> >>>>>> +                -I$INST_DIR/$PREFIX/include" \
> >>>>>> +              --extra-ldflags="-L$INST_DIR/$PREFIX/lib 
> >>>>>> -Wl,-rpath-link=$INST_DIR/$PREFIX/lib \
> >>>>>>                           -L$INST_DIR/$PREFIX/lib64 
> >>>>>> -Wl,-rpath-link=$INST_DIR/$PREFIX/lib64" \
> >>>>>> -        --disable-kvm \
> >>>>>> -        --disable-docs \
> >>>>>> -        --bindir=$PREFIX/lib/xen/bin \
> >>>>>> -        --datadir=$PREFIX/share/qemu-xen \
> >>>>>> -        --disable-guest-agent
> >>>>>> +              --bindir=$PREFIX/lib/xen/bin \
> >>>>>> +              --datadir=$PREFIX/share/qemu-xen \
> >>>>>> +              --disable-kvm \
> >>>>>> +              --disable-docs \
> >>>>>> +              --disable-guest-agent
> >>>>>
> >>>>> This is adding XC_WANT_COMPAT_EVTCHN_API=1, etc, unconditionally. If we
> >>>>> make this change, will raisin still be able to buil an older qemu
> >>>>> against an older xen?
> >>>>
> >>>> I've tested this with XEN_RELEASE set to 4.5 and 4.6, and it builds just
> >>>> fine.  The #define is just ignored, since neither Xen nor qemu in the
> >>>> 4.5 and 4.6 branches know anything about it.
> >>>>
> >>>> If part of our goal is to be a repository of the canonical way to build
> >>>> things, though, perhaps it would be better to have the extra flags be
> >>>> conditional on the value of XEN_RELEASE.
> >>>
> >>> If we are sure that it's ignored than it might be benign. Maybe we
> >>> should just add an in-code comment to explain why we added it though.
> >>
> >> Well really, I think that the detection should be put into the qemu
> >> configure scripts -- i.e., it should detect that there's the new API and
> >> add the appropriate #defines itself.  But that's the sort of change I
> >> don't think there will be a lot of enthusiasm for. :-)
> > 
> > Actually there is already code in QEMU configure script for the
> > detection. In fact I was wondering if explicitly passing XC_WANT_* is
> > actually necessary. I don't think it is from QEMU POV.
> 
> That code might be in qemu-upstream, but it's not in the qemu-xen trees;
> if you revert this bit of the patch and try to build with raisin it will
> fail.  That's why I even bothered to add these in in the first place;
> and why IanC added these runes to tools/Makefile.
> 
> Anthony, can you comment more authoritatively here on what's going on?

Yes, easy, xen-4.7 introduce a new API but qemu-xen-4.7 does not know
about it, so qemu-xen will fail to compile. But there are some magic
flags that are use to provide an compatible API and can qemu-xen
compile.

QEMU have been taught about the new API and will use it, without the
magic flags. QEMU will actually ignore the magic flags with a bunch of
#undef.

> Would it be possible for 4.7.1 to backport the configure auto-detection
> stuff?

I think that would be possible. But backporting the use of the new api
will probably be harder. I guess we could just have qemu-xen define the
magic flags itself instead of relying on them been given via a configure
option.


Is that answer your questions?

-- 
Anthony PERARD

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