[Xen-devel] [PATCH] libxl, buildmakevars2file: Do not relink libxl each time

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Make Config.mk's definition of buildmakevars2file and
tools/libxl/Makefile's rule for _libxl_paths.h generate their files to
temporary files and only rename them into place if the intended file
has changed.  This gets rid of unnecessarily compilation and link
steps.

Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>

diff -r 81c40c5db26e Config.mk
--- a/Config.mk Mon Sep 20 16:57:08 2010 +0100
+++ b/Config.mk Mon Sep 20 17:04:34 2010 +0100
@@ -104,16 +104,17 @@ define buildmakevars2file-closure
 define buildmakevars2file-closure
     .PHONY: genpath
     genpath:
-       rm -f $(1);                                                    \
-       echo "SBINDIR=\"$(SBINDIR)\"" >> $(1);                         \
-       echo "BINDIR=\"$(BINDIR)\"" >> $(1);                           \
-       echo "LIBEXEC=\"$(LIBEXEC)\"" >> $(1);                         \
-       echo "LIBDIR=\"$(LIBDIR)\"" >> $(1);                           \
-       echo "SHAREDIR=\"$(SHAREDIR)\"" >> $(1);                       \
-       echo "PRIVATE_BINDIR=\"$(PRIVATE_BINDIR)\"" >> $(1);           \
-       echo "XENFIRMWAREDIR=\"$(XENFIRMWAREDIR)\"" >> $(1);           \
-       echo "XEN_CONFIG_DIR=\"$(XEN_CONFIG_DIR)\"" >> $(1);           \
-       echo "XEN_SCRIPT_DIR=\"$(XEN_SCRIPT_DIR)\"" >> $(1)
+       rm -f $(1).tmp;                                                    \
+       echo "SBINDIR=\"$(SBINDIR)\"" >> $(1).tmp;                         \
+       echo "BINDIR=\"$(BINDIR)\"" >> $(1).tmp;                           \
+       echo "LIBEXEC=\"$(LIBEXEC)\"" >> $(1).tmp;                         \
+       echo "LIBDIR=\"$(LIBDIR)\"" >> $(1).tmp;                           \
+       echo "SHAREDIR=\"$(SHAREDIR)\"" >> $(1).tmp;                       \
+       echo "PRIVATE_BINDIR=\"$(PRIVATE_BINDIR)\"" >> $(1).tmp;           \
+       echo "XENFIRMWAREDIR=\"$(XENFIRMWAREDIR)\"" >> $(1).tmp;           \
+       echo "XEN_CONFIG_DIR=\"$(XEN_CONFIG_DIR)\"" >> $(1).tmp;           \
+       echo "XEN_SCRIPT_DIR=\"$(XEN_SCRIPT_DIR)\"" >> $(1).tmp;           \
+       if ! cmp $(1).tmp $(1); then mv -f $(1).tmp $(1); fi
 endef
 
 ifeq ($(debug),y)
diff -r 81c40c5db26e tools/libxl/Makefile
--- a/tools/libxl/Makefile      Mon Sep 20 16:57:08 2010 +0100
+++ b/tools/libxl/Makefile      Mon Sep 20 17:04:34 2010 +0100
@@ -52,12 +52,12 @@ all: $(CLIENTS) libxenlight.so libxenlig
        @rm -f $*.[ch]
        $(FLEX) --header-file=$*.h --outfile=$*.c $<
 
-genpath-target = $(call buildmakevars2file,_libxl_paths.h)
+genpath-target = $(call buildmakevars2file,_libxl_paths.h.tmp)
 $(eval $(genpath-target))
 
 _libxl_paths.h: genpath
-       sed -e "s/\([^=]*\)=\(.*\)/#define \1 \2/g" $@ >_$@
-       mv _$@ $@
+       sed -e "s/\([^=]*\)=\(.*\)/#define \1 \2/g" $@.tmp >$@.2.tmp
+       if ! cmp $@.2.tmp $@; then mv -f $@.2.tmp $@; fi
 
 libxl_paths.c: _libxl_paths.h
 

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