[Xen-changelog] [xen master] tools: probe for existence of qemu-xen stderr trace backend.

[patchbot@xxxxxxx]

commit f9b880721cd0ffa207faf90af9b02e2df3b57393
Author:     Ian Campbell <ian.campbell@xxxxxxxxxx>
AuthorDate: Thu Feb 11 12:11:21 2016 +0000
Commit:     Ian Campbell <ian.campbell@xxxxxxxxxx>
CommitDate: Thu Feb 11 16:33:54 2016 +0000

    tools: probe for existence of qemu-xen stderr trace backend.
    
    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@xxxxxxxxxx>
    Cc: Paul Durrant <paul.durrant@xxxxxxxxxx>
    Cc: Anthony PERARD <anthony.perard@xxxxxxxxxx>
    Reviewed-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
    Reviewed-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
    Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>
---
 tools/Makefile | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/tools/Makefile b/tools/Makefile
index cb8652c..3f45fb9 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -228,7 +228,7 @@ qemu-xen-dir-force-update: qemu-xen-dir-find
        fi
 
 ifeq ($(debug),y)
-QEMU_XEN_ENABLE_DEBUG := --enable-debug --enable-trace-backend=stderr
+QEMU_XEN_ENABLE_DEBUG := --enable-debug
 else
 QEMU_XEN_ENABLE_DEBUG :=
 endif
@@ -240,8 +240,14 @@ subdir-all-qemu-xen-dir: qemu-xen-dir-find
                source=.; \
        fi; \
        cd qemu-xen-dir; \
+       if $$source/scripts/tracetool.py --check-backend --backend stderr ; 
then \
+               enable_trace_backend='--enable-trace-backend=stderr'; \
+       else \
+               enable_trace_backend='' ; \
+       fi ; \
        $$source/configure --enable-xen --target-list=i386-softmmu \
                $(QEMU_XEN_ENABLE_DEBUG) \
+               $$enable_trace_backend \
                --prefix=$(LIBEXEC) \
                --libdir=$(LIBEXEC_LIB) \
                --includedir=$(LIBEXEC_INC) \
--
generated by git-patchbot for /home/xen/git/xen.git#master

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