[PATCH] fs/proc: add compile time info

[Florian Eckert <fe@xxxxxxxxxx>]

We already have this information available during the build process.
This information is output in the first line of the boot log during the
boot process.

Unfortunately, this information is only readbale humans when
they look at the first line of the boolog. In order for this information
to be further processed by the machine and other userland services,
it should be separately readable as epoch date in the proc directory.

Signed-off-by: Florian Eckert <fe@xxxxxxxxxx>
---
 fs/proc/Makefile       |  1 +
 fs/proc/compile_time.c | 20 ++++++++++++++++++++
 scripts/mkcompile_h    |  5 ++++-
 3 files changed, 25 insertions(+), 1 deletion(-)
 create mode 100644 fs/proc/compile_time.c

diff --git a/fs/proc/Makefile b/fs/proc/Makefile
index bd08616ed8ba..ee61a8c2c840 100644
--- a/fs/proc/Makefile
+++ b/fs/proc/Makefile
@@ -23,6 +23,7 @@ proc-y	+= stat.o
 proc-y	+= uptime.o
 proc-y	+= util.o
 proc-y	+= version.o
+proc-y	+= compile_time.o
 proc-y	+= softirqs.o
 proc-y	+= namespaces.o
 proc-y	+= self.o
diff --git a/fs/proc/compile_time.c b/fs/proc/compile_time.c
new file mode 100644
index 000000000000..4cf659d3c28c
--- /dev/null
+++ b/fs/proc/compile_time.c
@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <generated/compile.h>
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+
+static int compile_time_proc_show(struct seq_file *m, void *v)
+{
+	seq_printf(m, "%s\n", LINUX_COMPILE_EPOCH);
+	return 0;
+}
+
+static int __init proc_compile_time_init(void)
+{
+	proc_create_single("compile_time", 0, NULL, compile_time_proc_show);
+	return 0;
+}
+
+fs_initcall(proc_compile_time_init);
diff --git a/scripts/mkcompile_h b/scripts/mkcompile_h
index ca40a5258c87..d0e927602276 100755
--- a/scripts/mkcompile_h
+++ b/scripts/mkcompile_h
@@ -24,8 +24,10 @@ else
 fi
 
 if [ -z "$KBUILD_BUILD_TIMESTAMP" ]; then
-	TIMESTAMP=`date`
+	LINUX_COMPILE_EPOCH=$(date +%s)
+	TIMESTAMP=$(date -d "@$LINUX_COMPILE_EPOCH")
 else
+	LINUX_COMPILE_EPOCH=$(date -d "$KBUILD_BUILD_TIMESTAMP" +%s)
 	TIMESTAMP=$KBUILD_BUILD_TIMESTAMP
 fi
 if test -z "$KBUILD_BUILD_USER"; then
@@ -64,6 +66,7 @@ UTS_VERSION="$(echo $UTS_VERSION $CONFIG_FLAGS $TIMESTAMP | cut -b -$UTS_LEN)"
 
   echo \#define UTS_VERSION \"$UTS_VERSION\"
 
+  printf '#define LINUX_COMPILE_EPOCH "%s"\n' "$LINUX_COMPILE_EPOCH"
   printf '#define LINUX_COMPILE_BY "%s"\n' "$LINUX_COMPILE_BY"
   echo \#define LINUX_COMPILE_HOST \"$LINUX_COMPILE_HOST\"
 
-- 
2.30.2