Re: [PATCH v2] tools: probe for existence of qemu-xen stderr trace backend.

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

On Thu, 2016-02-11 at 16:30 +0000, Wei Liu wrote:
> On Thu, Feb 11, 2016 at 12:11:21PM +0000, Ian Campbell wrote:
> > QEMU upstream commit ed7f5f1d8db0 ("trace: convert stderr backend to
> > log") renamed the "stderr" trace backend to "log", which breaks the
> > xen build when pointed at a QEMU tree after that point:
> > 
> > ./configure of QEMU fail with:
> > "ERROR: invalid trace backends
> >         Please choose supported trace backends."
> > 
> > Upstream also changed, in baf86d6b3ca0 ("trace: switch default backend
> > to "log""), to use "log" as the default backend (previously it was
> > "nop").
> > 
> > Use ./scripts/tracetool.py to check for the presence of the stderr
> > backend and if it is present then explicitly enable it. If the stderr
> > backend is not present then assume a newer QEMU which defaults to
> > "log" and simply accept that default (there is a 1 commit window
> > upstream where this would result in no trace backend being enabled).
> > 
> > The check is done using the older (deprecated?) --check-backend/
> > --backend
> > variant of the tracetool.py options rather than the new plural
> > versions since the singular was supported even by very old versions of
> > QEMU.  New QEMU has compatibility code but if/when that is removed we
> > will still do the right thing i.e. no explict configuiration resulting
> > in the upstream default (currently "log").
> > 
> > If the explicit selection of the "stderr" backend is required then it
> > is now done unconditionally (not depending on debug=y), which is
> > simpler to arrange here but also matches the newer upstream's default
> > to "log" which is not conditional on debug being enabled either.
> > 
> > Tested with current qemu-xen-unstable (e9d8252) and current QEMU
> > upstream master (88c73d1), both out of tree via
> > QEMU_UPSTREAM_URL=/path/to/qemu-xen.git.
> > 
> > Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
> > Cc: Paul Durrant <paul.durrant@citrix.com>
> > Cc: Anthony PERARD <anthony.perard@citrix.com>
> 
> Acked-by: Wei Liu <wei.liu2@citrix.com>

Thanks, applied.


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