linux-kernel - [PATCH 2/2] initramfs: Encode dependency on KBUILD_BUILD

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Message-Id: <20230320040839.660475-2-bgray@linux.ibm.com>
Date:   Mon, 20 Mar 2023 15:08:39 +1100
From:   Benjamin Gray <bgray@...ux.ibm.com>
To:     linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org
Cc:     Benjamin Gray <bgray@...ux.ibm.com>
Subject: [PATCH 2/2] initramfs: Encode dependency on KBUILD_BUILD_TIMESTAMP

gen_initramfs.sh has an internal dependency on KBUILD_BUILD_TIMESTAMP
for generating file mtimes that is not exposed to make, so changing
KBUILD_BUILD_TIMESTAMP will not trigger a rebuild of the archive.

Declare the mtime date as a new parameter to gen_initramfs.sh to encode
KBUILD_BUILD_TIMESTAMP in the shell command, thereby making make aware
of the dependency.

It will rebuild if KBUILD_BUILD_TIMESTAMP changes or is newly set/unset.
It will _not_ rebuild if KBUILD_BUILD_TIMESTAMP is unset before and
after. This should be fine for anyone who doesn't care about setting
specific build times in the first place.

Signed-off-by: Benjamin Gray <bgray@...ux.ibm.com>

---

Ran into this while debugging the issue in the first patch. Made for a
very perplexing debug session before we worked out the state wasn't
being rebuilt.
---
 usr/Makefile         |  2 ++
 usr/gen_initramfs.sh | 16 +++++++++-------
 2 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/usr/Makefile b/usr/Makefile
index 59d9e8b07a01..2aa386cf48d6 100644
--- a/usr/Makefile
+++ b/usr/Makefile
@@ -64,6 +64,7 @@ quiet_cmd_initfs = GEN     $@
 	$(CONFIG_SHELL) $< -o $@ -l $(obj)/.initramfs_data.cpio.d \
 	$(if $(CONFIG_INITRAMFS_ROOT_UID), -u $(CONFIG_INITRAMFS_ROOT_UID)) \
 	$(if $(CONFIG_INITRAMFS_ROOT_GID), -g $(CONFIG_INITRAMFS_ROOT_GID)) \
+	$(if $(KBUILD_BUILD_TIMESTAMP), -d $(KBUILD_BUILD_TIMESTAMP)) \
 	$(ramfs-input)
 
 # We rebuild initramfs_data.cpio if:
@@ -71,6 +72,7 @@ quiet_cmd_initfs = GEN     $@
 # 2) There are changes in which files are included (added or deleted)
 # 3) If gen_init_cpio are newer than initramfs_data.cpio
 # 4) Arguments to gen_initramfs.sh changes
+# 5) KBUILD_BUILD_TIMESTAMP is changed
 $(obj)/initramfs_data.cpio: $(src)/gen_initramfs.sh $(obj)/gen_init_cpio $(deps_initramfs) FORCE
 	$(call if_changed,initfs)
 
diff --git a/usr/gen_initramfs.sh b/usr/gen_initramfs.sh
index 63476bb70b41..14b5782f961a 100755
--- a/usr/gen_initramfs.sh
+++ b/usr/gen_initramfs.sh
@@ -23,6 +23,7 @@ $0 [-o <file>] [-l <dep_list>] [-u <uid>] [-g <gid>] {-d | <cpio_source>} ...
 	-g <gid>       Group ID to map to group ID 0 (root).
 		       <gid> is only meaningful if <cpio_source> is a
 		       directory.  "squash" forces all files to gid 0.
+	-d <date>      Use date for all file mtime values
 	<cpio_source>  File list or directory for cpio archive.
 		       If <cpio_source> is a .cpio file it will be used
 		       as direct input to initramfs.
@@ -190,6 +191,7 @@ prog=$0
 root_uid=0
 root_gid=0
 dep_list=
+timestamp=
 cpio_list=$(mktemp ${TMPDIR:-/tmp}/cpiolist.XXXXXX)
 output="/dev/stdout"
 
@@ -218,6 +220,13 @@ while [ $# -gt 0 ]; do
 			[ "$root_gid" = "-1" ] && root_gid=$(id -g || echo 0)
 			shift
 			;;
+		"-d")	# date for file mtimes
+			timestamp="$(date -d"$1" +%s || :)"
+			if test -n "$timestamp"; then
+				timestamp="-t $timestamp"
+			fi
+			shift
+			;;
 		"-h")
 			usage
 			exit 0
@@ -237,11 +246,4 @@ done
 
 # If output_file is set we will generate cpio archive
 # we are careful to delete tmp files
-timestamp=
-if test -n "$KBUILD_BUILD_TIMESTAMP"; then
-	timestamp="$(date -d"$KBUILD_BUILD_TIMESTAMP" +%s || :)"
-	if test -n "$timestamp"; then
-		timestamp="-t $timestamp"
-	fi
-fi
 usr/gen_init_cpio $timestamp $cpio_list > $output
-- 
2.39.2