[PATCH v3] stubdom: modify ioemu linkfarm only if necessary

[Juergen Gross <jgross@suse.com>]

Several stubdom libraries are being rebuilt each time a top level make
is called as they depend on stubdom/ioemu/linkfarm.stamp which is
depending on tools/qemu-xen-traditional-dir. Unfortunately this
directory is modified by each "make tools" call.

This can be avoided by writing stubdom/ioemu/linkfarm.stamp only if
a source file beneath tools/qemu-xen-traditional-dir has been added
or removed.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
---
V3: use cmp -s as suggested by Wei Liu

V2: maintain a list of the to be linked files in linkfarm.stamp and
    rebuild this list at each make call for detecting any change
---
 stubdom/Makefile | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/stubdom/Makefile b/stubdom/Makefile
index bc49cfe..f858210 100644
--- a/stubdom/Makefile
+++ b/stubdom/Makefile
@@ -298,9 +298,13 @@ ioemu/linkfarm.stamp: $(XEN_ROOT)/tools/qemu-xen-traditional-dir
 	(cd $$src && find *	! -type l  -type f  $(addprefix ! -name ,	\
 			'*.[oda1]' 'config-*' config.mak qemu-dm qemu-img-xen	\
 			'*.html' '*.pod'					\
-			)) |							\
-	    while read f; do rm -f "$$f"; ln -s "$$src/$$f" "$$f"; done
-	touch ioemu/linkfarm.stamp
+			)) >linkfarm.stamp.tmp;				\
+	cmp -s linkfarm.stamp.tmp linkfarm.stamp &&			\
+		rm linkfarm.stamp.tmp || {				\
+		mv linkfarm.stamp.tmp linkfarm.stamp;			\
+		cat linkfarm.stamp | while read f;			\
+			do rm -f "$$f"; ln -s "$$src/$$f" "$$f"; done;	\
+	}
 else
 export QEMU_ROOT
 
-- 
2.10.2


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