[OE-core] [PATCH] cpio rootfs build: Avoid modifying rootfs dir

[Jonas Eriksson]

The Linux kernel requires that initrd images contain a /init file for
the image to be used as an initrd, even if it is empty. Adding it into
the rootfs directory creates a race, that can upset tar when building
both a .tar and .cpio image file ("tar: .: file changed as we read it").
Additionally, whether or not the tar file will contain the /init file is
also up to the race condition.

To avoid this problem, move the /init addition out from the rootfs
directory, and thus only include it in the .cpio image.

Signed-off-by: Jonas Eriksson <jonas.eriksson at enea.com>
Signed-off-by: Josep Puigdemont <josep.puigdemont at enea.com>
Cc: Laurentiu Palcu <laurentiu.palcu at intel.com>
---
 meta/classes/image_types.bbclass | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/meta/classes/image_types.bbclass b/meta/classes/image_types.bbclass
index 602c1f0..8001025 100644
--- a/meta/classes/image_types.bbclass
+++ b/meta/classes/image_types.bbclass
@@ -67,10 +67,12 @@ IMAGE_CMD_squashfs-xz = "mksquashfs ${IMAGE_ROOTFS} ${DEPLOY_DIR_IMAGE}/${IMAGE_
 IMAGE_CMD_tar = "tar -cvf ${DEPLOY_DIR_IMAGE}/${IMAGE_NAME}.rootfs.tar -C ${IMAGE_ROOTFS} ."
 
 IMAGE_CMD_cpio () {
-	if [ ! -L ${IMAGE_ROOTFS}/init ]; then
-		touch ${IMAGE_ROOTFS}/init
-	fi
 	(cd ${IMAGE_ROOTFS} && find . | cpio -o -H newc >${DEPLOY_DIR_IMAGE}/${IMAGE_NAME}.rootfs.cpio)
+	if [ ! -e ${IMAGE_ROOTFS}/init ]; then
+		mkdir -p ${WORKDIR}/cpio_append
+		touch ${WORKDIR}/cpio_append/init
+		(cd  ${WORKDIR}/cpio_append && echo ./init | cpio -oA -H newc -F ${DEPLOY_DIR_IMAGE}/${IMAGE_NAME}.rootfs.cpio)
+	fi
 }
 
 ELF_KERNEL ?= "${STAGING_DIR_HOST}/usr/src/kernel/${KERNEL_IMAGETYPE}"
-- 
1.9.0