Re: [Xen-devel] [PATCH] tools: probe for existence of qemu-xen trace backends.

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 10 Feb 2016, Ian Campbell wrote:
> On Wed, 2016-02-10 at 14:27 +0000, Ian Campbell wrote:
> > On Wed, 2016-02-10 at 14:18 +0000, Anthony PERARD wrote:
> > > On Wed, Feb 10, 2016 at 02:14:13PM +0000, Stefano Stabellini wrote:
> > > > On Wed, 10 Feb 2016, Ian Campbell wrote:
> > > > > diff --git a/tools/Makefile b/tools/Makefile
> > > > > index 5688a7c..76a2235 100644
> > > > > --- a/tools/Makefile
> > > > > +++ b/tools/Makefile
> > > > > @@ -228,7 +228,7 @@ qemu-xen-dir-force-update: qemu-xen-dir-find
> > > > > Â     fi
> > > > > Â
> > > > > Âifeq ($(debug),y)
> > > > > -QEMU_XEN_ENABLE_DEBUG := --enable-debug --enable-trace-
> > > > > backend=stderr
> > > > > +QEMU_XEN_ENABLE_DEBUG := --enable-debug
> > > > > Âelse
> > > > > ÂQEMU_XEN_ENABLE_DEBUG :=
> > > > > Âendif
> > > > > @@ -240,8 +240,16 @@ subdir-all-qemu-xen-dir: qemu-xen-dir-find
> > > > > Â             source=.; \
> > > > > Â     fi; \
> > > > > Â     cd qemu-xen-dir; \
> > > > > +     if $$source/scripts/tracetool.py --check-backends --
> > > > > backends
> > > > > log ; then \
> > > >
> > > > --check-backends only works on qemu-xen >= 4.6, on the other hand we
> > > > know that qemu-xen < 4.6 supports stderr.
> > >
> > > But, if you use '--check-backend --backend' (no 's') instead, the check
> > > would works with qemu-xen >= 4.3
>
> BTW, I think those correspond to
>
> qemu-mainline == QEMU 2.5.50
> qemu-xen-unstable == QEMU 2.4.1
> qemu-xen-4.6 == QEMU 2.2.1
> qemu-xen-4.5 == QEMU 2.0.2
>
> and the change to use --backends was betweenÂ2.0.50 andÂ2.0.90 (AKA 2.1.0-
> rc0).
>
> Do we require that Xen 4.7 will work with QEMU 2.0.x? Given that AFAICT the
> oldest QEMU upstream supported version is 2.2.1?

No, but if somebody wants to use qemu-xen-4.5 with xen-unstable, which
is not that crazy given that qemu-xen-4.5 is still supported (even
qemu-xen-4.3 still is), this change in the Makefile would break the
build. Anthony's suggestion is a good compromise.

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