[OE-core] [PATCH 1/2] kernel: stop using -exec rm for deleting files

[Bruce Ashfield]

Removing files from the source tree via find, exec and rm is not the
most efficient operation, due to (among other things) the many forked
processes.

If we use -delete, it saves a significant amount of time. But -delete
does not work with -prune (since it forces -depth). To maintain the
lib, tools and scripts source files, we can hide them temporarily,
skip their hidden directories and then finally restore them.

Time for install before this change:

 real    2m48.563s
 user    0m35.220s
 sys     0m33.036s

Time for install after this change:

 real    1m21.301s
 user    0m33.160s
 sys     0m28.388s

We could further speed this up by using inline perl to delete the files,
but that complexity is avoided for now.

Signed-off-by: Bruce Ashfield <bruce.ashfield at windriver.com>
---
 meta/classes/kernel.bbclass | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/meta/classes/kernel.bbclass b/meta/classes/kernel.bbclass
index 51626b03f824..b76a65699755 100644
--- a/meta/classes/kernel.bbclass
+++ b/meta/classes/kernel.bbclass
@@ -260,9 +260,21 @@ kernel_do_install() {
 	# we clean the scripts dir while leaving the generated config
 	# and include files.
 	#
-	oe_runmake -C $kerneldir CC="${KERNEL_CC}" LD="${KERNEL_LD}" clean
-	make -C $kerneldir _mrproper_scripts
-	find $kerneldir -path $kerneldir/lib -prune -o -path $kerneldir/tools -prune -o -path $kerneldir/scripts -prune -o -name "*.[csS]" -exec rm '{}' \;
+	oe_runmake -C $kerneldir CC="${KERNEL_CC}" LD="${KERNEL_LD}" clean _mrproper_scripts 
+
+	# hide directories that shouldn't have their .c, s and S files deleted
+	for d in tools scripts lib; do
+		mv $kerneldir/$d $kerneldir/.$d
+	done
+
+	# delete .c, .s and .S files, unless we hid a directory as .<dir>. This technique is 
+	# much faster than find -prune and -exec
+	find . -not -path '*/\.*' -type f -name "*.[csS]" -delete
+
+	# put the hidden dirs back
+	for d in tools scripts lib; do
+		mv $kerneldir/.$d $kerneldir/$d
+	done
 
 	# As of Linux kernel version 3.0.1, the clean target removes
 	# arch/powerpc/lib/crtsavres.o which is present in
-- 
1.8.1.2