initramfs: Use KBUILD_BUILD_TIMESTAMP for generated entries

gen_init_cpio gets the current time and uses it for each symlink,
special file, and directory.  Grab the current time once and make it
possible to override it with the KBUILD_BUILD_TIMESTAMP variable for
reproducible builds.
Signed-off-by: Michal Marek <mmarek@suse.cz>

Documentation/kbuild/kbuild.txt

@@ -205,7 +205,8 @@ gcc -W... options for more extensive build-time checking.
 KBUILD_BUILD_TIMESTAMP
 --------------------------------------------------
 Setting this to a date string overrides the timestamp used in the
-UTS_VERSION definition (uname -v in the running kernel). The default value
+UTS_VERSION definition (uname -v in the running kernel). The value has to
+be a string that can be passed to date -d. The default value
 is the output of the date command at one point during build.
 
 KBUILD_BUILD_USER, KBUILD_BUILD_HOST

scripts/gen_initramfs_list.sh

@@ -287,8 +287,15 @@ done
 # we are carefull to delete tmp files
 if [ ! -z ${output_file} ]; then
 	if [ -z ${cpio_file} ]; then
+		timestamp=
+		if test -n "$KBUILD_BUILD_TIMESTAMP"; then
+			timestamp="$(date -d"$KBUILD_BUILD_TIMESTAMP" +%s || :)"
+			if test -n "$timestamp"; then
+				timestamp="-t $timestamp"
+			fi
+		fi
 		cpio_tfile="$(mktemp ${TMPDIR:-/tmp}/cpiofile.XXXXXX)"
-		usr/gen_init_cpio ${cpio_list} > ${cpio_tfile}
+		usr/gen_init_cpio $timestamp ${cpio_list} > ${cpio_tfile}
 	else
 		cpio_tfile=${cpio_file}
 	fi

usr/gen_init_cpio.c

@@ -22,6 +22,7 @@
 
 static unsigned int offset;
 static unsigned int ino = 721;
+static time_t default_mtime;
 
 struct file_handler {
 	const char *type;
@@ -102,7 +103,6 @@ static int cpio_mkslink(const char *name, const char *target,
 			 unsigned int mode, uid_t uid, gid_t gid)
 {
 	char s[256];
-	time_t mtime = time(NULL);
 
 	if (name[0] == '/')
 		name++;
@@ -114,7 +114,7 @@ static int cpio_mkslink(const char *name, const char *target,
 		(long) uid,		/* uid */
 		(long) gid,		/* gid */
 		1,			/* nlink */
-		(long) mtime,		/* mtime */
+		(long) default_mtime,	/* mtime */
 		(unsigned)strlen(target)+1, /* filesize */
 		3,			/* major */
 		1,			/* minor */
@@ -152,7 +152,6 @@ static int cpio_mkgeneric(const char *name, unsigned int mode,
 		       uid_t uid, gid_t gid)
 {
 	char s[256];
-	time_t mtime = time(NULL);
 
 	if (name[0] == '/')
 		name++;
@@ -164,7 +163,7 @@ static int cpio_mkgeneric(const char *name, unsigned int mode,
 		(long) uid,		/* uid */
 		(long) gid,		/* gid */
 		2,			/* nlink */
-		(long) mtime,		/* mtime */
+		(long) default_mtime,	/* mtime */
 		0,			/* filesize */
 		3,			/* major */
 		1,			/* minor */
@@ -242,7 +241,6 @@ static int cpio_mknod(const char *name, unsigned int mode,
 		       unsigned int maj, unsigned int min)
 {
 	char s[256];
-	time_t mtime = time(NULL);
 
 	if (dev_type == 'b')
 		mode |= S_IFBLK;
@@ -259,7 +257,7 @@ static int cpio_mknod(const char *name, unsigned int mode,
 		(long) uid,		/* uid */
 		(long) gid,		/* gid */
 		1,			/* nlink */
-		(long) mtime,		/* mtime */
+		(long) default_mtime,	/* mtime */
 		0,			/* filesize */
 		3,			/* major */
 		1,			/* minor */
@@ -460,7 +458,7 @@ static int cpio_mkfile_line(const char *line)
 static void usage(const char *prog)
 {
 	fprintf(stderr, "Usage:\n"
-		"\t%s <cpio_list>\n"
+		"\t%s [-t <timestamp>] <cpio_list>\n"
 		"\n"
 		"<cpio_list> is a file containing newline separated entries that\n"
 		"describe the files to be included in the initramfs archive:\n"
@@ -491,7 +489,11 @@ static void usage(const char *prog)
 		"nod /dev/console 0600 0 0 c 5 1\n"
 		"dir /root 0700 0 0\n"
 		"dir /sbin 0755 0 0\n"
-		"file /sbin/kinit /usr/src/klibc/kinit/kinit 0755 0 0\n",
+		"file /sbin/kinit /usr/src/klibc/kinit/kinit 0755 0 0\n"
+		"\n"
+		"<timestamp> is time in seconds since Epoch that will be used\n"
+		"as mtime for symlinks, special files and directories. The default\n"
+		"is to use the current time for these entries.\n",
 		prog);
 }
 
@@ -529,17 +531,42 @@ int main (int argc, char *argv[])
 	char *args, *type;
 	int ec = 0;
 	int line_nr = 0;
+	const char *filename;
+
+	default_mtime = time(NULL);
+	while (1) {
+		int opt = getopt(argc, argv, "t:h");
+		char *invalid;
 
-	if (2 != argc) {
+		if (opt == -1)
+			break;
+		switch (opt) {
+		case 't':
+			default_mtime = strtol(optarg, &invalid, 10);
+			if (!*optarg || *invalid) {
+				fprintf(stderr, "Invalid timestamp: %s\n",
+						optarg);
+				usage(argv[0]);
+				exit(1);
+			}
+			break;
+		case 'h':
+		case '?':
+			usage(argv[0]);
+			exit(opt == 'h' ? 0 : 1);
+		}
+	}
+
+	if (argc - optind != 1) {
 		usage(argv[0]);
 		exit(1);
 	}
-
-	if (!strcmp(argv[1], "-"))
+	filename = argv[optind];
+	if (!strcmp(filename, "-"))
 		cpio_list = stdin;
-	else if (! (cpio_list = fopen(argv[1], "r"))) {
+	else if (!(cpio_list = fopen(filename, "r"))) {
 		fprintf(stderr, "ERROR: unable to open '%s': %s\n\n",
-			argv[1], strerror(errno));
+			filename, strerror(errno));
 		usage(argv[0]);
 		exit(1);
 	}