image.bbclass: make ext2/ext3 images autoresize

New variable IMAGE_EXTRA_SPACE contains amount of kilobytes which has
to be added to size of IMAGE_ROOTFS. Resulting size is then passed to
genext2fs util.

As a result we do not have to specify size for ROOTFS_SIZE anymore.

git-svn-id: https://svn.o-hand.com/repos/poky/trunk@5269 311d38ba-8fff-0310-9ca6-ca027cbcb966

meta/classes/image.bbclass

@@ -107,6 +107,7 @@ fakeroot do_rootfs () {
 
 	${IMAGE_PREPROCESS_COMMAND}
 
+	ROOTFS_SIZE=`du -ks ${IMAGE_ROOTFS}|awk '{print ${IMAGE_EXTRA_SPACE} + $1}'`
 	${@get_imagecmds(d)}
 
 	# Run ldconfig on the image to create a valid cache