[PATCH] kernel: Use hardlinks during do_install for speed

[Richard Purdie <richard.purdie@linuxfoundation.org>]

Whilst the comment says we can't do this, its incorrect, install operates
on WORKDIR and its hard for different parts of WORKDIR to be on different
filesystems. Hardlinking instead of copying is therefore a nice performance
gain.

Also, completely skip the Documentation directory (adding a dummy Makefile
to keep make happy) and tweak the other cp commands to link since if we
don't we'd get "this is the same file" type errors from cp for some kernel
versions.

For do_install on linux-yocto, this takes it from 227s -> 84s.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
---
diff --git a/meta/classes/kernel.bbclass b/meta/classes/kernel.bbclass
index a4db9f5..0b6360f 100644
--- a/meta/classes/kernel.bbclass
+++ b/meta/classes/kernel.bbclass
@@ -236,20 +236,21 @@ kernel_do_install() {
 	# dir. This ensures the original Makefiles are used and not the
 	# redirecting Makefiles in the build directory.
 	#
-	# work and sysroots can be on different partitions, so we can't rely on
-	# hardlinking, unfortunately.
-	#
-	find . -depth -not -name "*.cmd" -not -name "*.o" -not -path "./.*" -print0 | cpio --null -pdu $kerneldir
+	find . -depth -not -name "*.cmd" -not -name "*.o" -not -path "./Documentation*" -not -path "./.*" -print0 | cpio --null -pdlu $kerneldir
 	cp .config $kerneldir
 	if [ "${S}" != "${B}" ]; then
 		pwd="$PWD"
 		cd "${S}"
-		find . -depth -not -path "./.*" -print0 | cpio --null -pdu $kerneldir
+		find . -depth -not -path "./Documentation*" -not -path "./.*" -print0 | cpio --null -pdlu $kerneldir
 		cd "$pwd"
 	fi
 	install -m 0644 ${KERNEL_OUTPUT} $kerneldir/${KERNEL_IMAGETYPE}
 	install -m 0644 System.map $kerneldir/System.map-${KERNEL_VERSION}
 
+	# Dummy Makefile so the clean below works
+        mkdir $kerneldir/Documentation
+        touch $kerneldir/Documentation/Makefile
+
 	#
 	# Clean and remove files not needed for building modules.
 	# Some distributions go through a lot more trouble to strip out
@@ -262,22 +263,21 @@ kernel_do_install() {
 	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 '{}' \;
-	find $kerneldir/Documentation -name "*.txt" -exec rm '{}' \;
 
 	# As of Linux kernel version 3.0.1, the clean target removes
 	# arch/powerpc/lib/crtsavres.o which is present in
 	# KBUILD_LDFLAGS_MODULE, making it required to build external modules.
 	if [ ${ARCH} = "powerpc" ]; then
-		cp arch/powerpc/lib/crtsavres.o $kerneldir/arch/powerpc/lib/crtsavres.o
+		cp -nl arch/powerpc/lib/crtsavres.o $kerneldir/arch/powerpc/lib/crtsavres.o
 	fi
 
 	# Necessary for building modules like compat-wireless.
 	if [ -f include/generated/bounds.h ]; then
-		cp include/generated/bounds.h $kerneldir/include/generated/bounds.h
+		cp -nl include/generated/bounds.h $kerneldir/include/generated/bounds.h
 	fi
 	if [ -d arch/${ARCH}/include/generated ]; then
 		mkdir -p $kerneldir/arch/${ARCH}/include/generated/
-		cp -fR arch/${ARCH}/include/generated/* $kerneldir/arch/${ARCH}/include/generated/
+		cp -fnlR arch/${ARCH}/include/generated/* $kerneldir/arch/${ARCH}/include/generated/
 	fi
 
 	# Remove the following binaries which cause strip or arch QA errors