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 $$source/scripts/tracetool.py --check-backends --
> > > > > backends
> > > > > log ; then \
> > > >
> > > > --check-backends only works on qemu-xen >= 4.6, on the other hand we
> > > > know that qemu-xen < 4.6 supports stderr.
> > >
> > > But, if you use '--check-backend --backend' (no 's') instead, the check
> > > would works with qemu-xen >= 4.3
> >
> > That would be preferable to the below, IMHO. Any contrary opinions?
>
> Actually, given that the upstream default is now "log", how about:
>
> Â Â Â Â if $$source/scripts/tracetool.py --check-backend --backend stderr ; 
> then \
>               enable_trace_backend='--enable-trace-backend=stderr'; \
>       else \          enable_trace_backend='' ; \
>
> Â Â Â Â fi ; \
>
> IOW just accept the upstream default (be it log or whatever comes next)
> from this version onwards?

The risk associated with that is that in the past QEMU recommended
'simple', which has a binary output to a separate file.

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