mke2fs: warn about missing y2038 support when formatting fresh ext4 fs

From: Darrick J. Wong <[email protected]>

Filesystems with 128-byte inodes do not support timestamps beyond the year 2038. Since we're now less than 16.5 years away from that point, it's time to start warning users about this lack of support when they format an ext4 filesystem with small inodes.

First, change the mke2fs.conf file to specify 256-byte inodes even for small filesystems, then add a warning to mke2fs itself if someone is trying to make us format an ext4 filesystem with 128-byte inodes.

Note that we /don't/ warn about these things if the user has signalled that they want an old format such as ext2, ext3, or hurd. Everyone should know by now that those are legacy.

Signed-off-by Darrick J. Wong <[email protected]>

---
misc/mke2fs.c | 35 +++++++++++++++++++++++++++++++++++
misc/mke2fs.conf.in | 4 ++--

2 files changed, 37 insertions(+), 2 deletions(-)

misc/mke2fs.c +35 -0

index 92003e11..b16880c2 100644
@@ -1537,6 +1537,30 @@ static int get_device_geometry(const char *file,
 }
 #endif
 
+/*
+ * Returns true if the user is forcing an old format (e.g. ext2, ext3).
+ *
+ * If there is no fs_types list, the user invoked us with no explicit type and
+ * gets the default (ext4) format.  If we find the latest format (ext4) in the
+ * type list, some combination of program name and -T argument put us in ext4
+ * mode.  Anything else (ext2, ext3, hurd) and we return false.
+ */
+static inline int
+old_format_forced(char **fs_types)
+{
+	int found_ext4 = 0;
+	int i;
+
+	if (!fs_types)
+		return 0;
+
+	for (i = 0; fs_types[i]; i++)
+		if (!strcmp(fs_types[i], "ext4"))
+			found_ext4 = 1;
+
+	return !found_ext4;
+}
+
 static void PRS(int argc, char *argv[])
 {
 	int		b, c, flags;

@@ -2603,6 +2627,17 @@ static void PRS(int argc, char *argv[])
 		exit(1);
 	}
 
+	/* If the user didn't tell us to format with an old ondisk format... */
+	if (!old_format_forced(fs_types)) {
+		/*
+		 * ...warn them that filesystems with 128-byte inodes will not
+		 * work properly beyond 2038.
+		 */
+		if (inode_size == EXT2_GOOD_OLD_INODE_SIZE)
+			printf(
+_("128-byte inodes cannot handle dates beyond 2038 and are deprecated\n"));
+	}
+
 	/* Make sure number of inodes specified will fit in 32 bits */
 	if (num_inodes == 0) {
 		unsigned long long n;

misc/mke2fs.conf.in +0 -1

index 01e35cf8..2fa1a824 100644
@@ -16,12 +16,12 @@
 	}
 	small = {
 		blocksize = 1024
-		inode_size = 128

+/*
+ * Returns true if the user is forcing an old format (e.g. ext2, ext3).
+ *
+ * If there is no fs_types list, the user invoked us with no explicit type and
+ * gets the default (ext4) format. If we find the latest format (ext4) in the
+ * type list, some combination of program name and -T argument put us in ext4
+ * mode. Anything else (ext2, ext3, hurd) and we return false.
+ */

Quoted 8 lines · Darrick J. Wong

+/*
+ * Returns true if the user is forcing an old format (e.g. ext2, ext3).
+ *
+ * If there is no fs_types list, the user invoked us with no explicit type and
+ * gets the default (ext4) format. If we find the latest format (ext4) in the
+ * type list, some combination of program name and -T argument put us in ext4
+ * mode. Anything else (ext2, ext3, hurd) and we return false.
+ */

So that's not actually quite right. Even if the user has no explicit type, mke2fs will assign a default type --- and it's not necessarily ext4. You can see what the contents of the fs_types list using the -v option:

% /bin/rm /tmp/foo.img ; mke2fs -vq /tmp/foo.img 8m fs_types for mke2fs.conf resolution: 'ext2', 'small' % /bin/rm /tmp/foo.img ; mke2fs -vq -T news /tmp/foo.img 8m fs_types for mke2fs.conf resolution: 'ext2', 'news' % /bin/rm /tmp/foo.img ; mkfs.ext4 -vq /tmp/foo.img 8m fs_types for mke2fs.conf resolution: 'ext4', 'small' % /bin/rm /tmp/foo.img ; mkfs.ext4 -T huge -vq /tmp/foo.img 8m fs_types for mke2fs.conf resolution: 'ext4', 'huge' % /bin/rm /tmp/foo.img ; mkfs.ext4 -o hurd -vq /tmp/foo.img 8m fs_types for mke2fs.conf resolution: 'ext2', 'small', 'hurd'

Also note that the ext2/ext3/ext4 fs_type will always be in fs_types[0], so it's not necessary to search the entire list, as the patch is currently doing:

misc/mke2fs.c static int get_device_geometry(const char *file, · line 1559

Quoted 4 lines

misc/mke2fs.c +3 -0

+	for (i = 0; fs_types[i]; i++)
+		if (!strcmp(fs_types[i], "ext4"))
+			found_ext4 = 1;

Cheers,

- Ted

P.S. Although I'm not aware of anyone actually doing this, if there mke2fs is installed as mke3fs or mke4fs, that's the equivalent of mkfs.ext3 and mkfs.ext4. (See the logic in the parse_fs_type function.) Although perhaps there is some obscure distro somewhere out there that I don't know about....