[PATCH] image.bbclass: set file timestamps inside the rootfs and initramfs image

[venkata.pyla@toshiba-tsip.com]

From: venkata pyla <venkata.pyla@toshiba-tsip.com>

As part of reproducible-build work, one of the problem chosen to solve
is the file time stamps inside rootfs and initramfs are not identical
between two builds.

With the help of reproducible-builds.org and their suggestions, the
above problem can be fixed using 'SOURCE_DATE_EPOCH' variable [2].

In case of rootfs file time-stamps, set all the files and folders that
are newer than 'SOURCE_DATE_EPOCH' and set it to same.
In case of initramfs, regenerate the initramfs image with
'SOURCE_DATE_EPOCH' variable set as the mkinitramfs script is already
taken care of creating reproducible initramfs image when the
variable is set in the environment[3].

The SOURCE_DATE_EPOCH variable should be set to the last modification of
the git repository as explained in the documentation[2].

e.g:
SOURCE_DATE_EPOCH=$(git log -1 --pretty=%ct)

To know more about the reproducible builds and its goals please refer [1].

[1] https://reproducible-builds.org/
[2] https://reproducible-builds.org/docs/source-date-epoch/
[3] https://manpages.debian.org/bullseye/initramfs-tools-core/mkinitramfs.8.en.html#ENVIRONMENT

Signed-off-by: venkata pyla <venkata.pyla@toshiba-tsip.com>
---
 meta/classes/image.bbclass | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/meta/classes/image.bbclass b/meta/classes/image.bbclass
index ccff810..c1bb4fd 100644
--- a/meta/classes/image.bbclass
+++ b/meta/classes/image.bbclass
@@ -431,6 +431,21 @@ do_rootfs_finalize() {
             "${ROOTFSDIR}/etc/apt/sources.list.d/bootstrap.list"
 
         rm -f "${ROOTFSDIR}/etc/apt/sources-list"
+
+        # Recreate initramfs inorder to set timestamps to SOURCE_DATE_EPOCH
+        # inorder to make reproducible initramfs
+        test ! -z "${SOURCE_DATE_EPOCH}" && \
+           SOURCE_DATE_EPOCH=${SOURCE_DATE_EPOCH} chroot "${ROOTFSDIR}" \
+                  update-initramfs -u -v
+
+	# Set timestamp to files inside the rootfs image inorder to make
+	# reproducible rootfs
+	test ! -z "${SOURCE_DATE_EPOCH}" && \
+           find ${ROOTFSDIR} -newermt \
+               "$(date -d@${SOURCE_DATE_EPOCH} '+%Y-%m-%d %H:%M:%S')" \
+               -printf "%y %p\n" \
+               -exec touch '{}' -h -d@${SOURCE_DATE_EPOCH} ';'
+
 EOSUDO
 }
 addtask rootfs_finalize before do_rootfs after do_rootfs_postprocess
-- 
2.20.1