[PATCH v1 1/1] imagetypes.bbclass: Generate reproducible ext4 images using IMAGE_CMD

[Adithya Balakumar]

e2fsprogs v1.47.1 added support for timestamp clamping to SOURCE_DATE_EPOCH
to generate reproducible ext4 images.

Along with the above, a deterministic uuid and hash_seed also needs to be set.

Signed-off-by: Adithya Balakumar <Adithya....@toshiba-tsip.com>
---
meta/classes/imagetypes.bbclass | 23 ++++++++++++++++++++++-
1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/meta/classes/imagetypes.bbclass b/meta/classes/imagetypes.bbclass
index a3be0a1d..f802c11c 100644
--- a/meta/classes/imagetypes.bbclass
+++ b/meta/classes/imagetypes.bbclass
@@ -14,9 +14,30 @@ IMAGE_CMD:tar() {

# image type: ext4
IMAGER_INSTALL:ext4 += "e2fsprogs"
-MKE2FS_ARGS ?= "-t ext4"

+# NOTE: Creating reproducible ext4 images requires timestamp clamping to SOURCE_DATE_EPOCH and deterministic uuid, hash_seed to be set.
+# Timestamp clamping to SOURCE_DATE_EPOCH is only available from e2fsprogs v1.47.1 onwards. Older versions cannot generate reproducible ext4 images.
+python set_mke2fs_args () {
+ import uuid
+
+ mke2fs_args = "-t ext4"
+ sde_time = int(os.getenv('SOURCE_DATE_EPOCH'))
+
+ # set uuid
+ fsuuid = uuid.UUID(int=sde_time)
+ mke2fs_args += " -U " + str(fsuuid)
+
+ # set hash_seed
+ hash_seed = str(uuid.uuid5(fsuuid, str(sde_time)))
+ mke2fs_args += " -E hash_seed=" + hash_seed
+
+ d.setVar("MKE2FS_ARGS", mke2fs_args)
+}
+
+do_image_ext4[prefuncs] = "set_mke2fs_args"
IMAGE_CMD:ext4() {
+ export E2FSPROGS_FAKE_TIME="${SOURCE_DATE_EPOCH}"
+
truncate -s ${ROOTFS_SIZE}K '${IMAGE_FILE_HOST}'

${SUDO_CHROOT} /sbin/mke2fs ${MKE2FS_ARGS} \
--
2.39.5