Kbuild regenerates bounds.h and asm-offsets.h, resetting the timestamps
and forcing rebuilds even if the contents haven't changed. Add a bit of
shell magic to only replace the file if the contents have in fact changed,
which should speed up git bisects and similar.
Signed-off-by: Valdis Kletnieks <valdis.kletni...@vt.edu>
---
So I was doing a git bisect, and getting towards the end, and wondering why
it's taking a long time for each build, and I notice that netfilter modules
are being rebuilt, even though 'git bisect visualize' doesn't show anything
that should have touched netfilter. Turns out the offender is bounds.h
Fully 3/4 of my modules have a dependency on bounds.h - and we touch it
all the time, even if the contents haven't changed.
RFC because I can't wrap my head around why this wasn't done ages ago.
If I'm missing something something obvious, please apply a cluestick. :)
Lightly tested - if I rm one of those two files, it gets rebuilt. If I
insert some whitespace, it gets replaced. If I don't touch it, the datestamp
doesn't change.
--- linux-next/Kbuild.dist 2015-03-03 19:50:45.175673346 -0500
+++ linux-next/Kbuild 2015-03-03 20:03:20.107820199 -0500
@@ -15,7 +15,7 @@
quiet_cmd_offsets = GEN $@
define cmd_offsets
- (set -e; \
+ ( (set -e; \
echo "#ifndef $2"; \
echo "#define $2"; \
echo "/*"; \
@@ -26,7 +26,10 @@
echo ""; \
sed -ne $(sed-y) $<; \
echo ""; \
- echo "#endif" ) > $@
+ echo "#endif" ) > $@.tmp; \
+ if [ ! -f $@ ]; then mv $@.tmp $@; \
+ elif cmp -s $@ $@.tmp ; then rm $@.tmp; \
+ else mv -f $@.tmp $@; fi )
endef
#####
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