[PATCH -v5] mke2fs: warn about missing y2038 support when formatting fresh ext4 fs

["Theodore Ts'o" <tytso@mit.edu>]

From: "Darrick J. Wong" <djwong@kernel.org>

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.

(Note that even for ext2 and ext3, we changed the default for
non-small file systems in 2008 in commit commit b1631cce648e ("Create
new filesystems with 256-byte inodes by default").)

So change the mke2fs.conf file to specify 256-byte inodes even for
small filesystems, and then add a warning to mke2fs itself if someone
is trying to make us format a file system with 128-byte inodes.  This
can be suppressed by setting the boolean option warn_y2038_dates in
the mke2fs.conf file to false, which we do in the case of GNU Hurd,
since it only supports 128 byte inodes as of this writing.

[ Patch reworked by tytso to only warn in the case of GNU Hurd, since
  the default for ext2/ext3 was changed for all but small file systems
  in 2008. ]

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
 misc/mke2fs.c         | 11 +++++++++++
 misc/mke2fs.conf.5.in |  7 +++++++
 misc/mke2fs.conf.in   |  4 +---
 3 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/misc/mke2fs.c b/misc/mke2fs.c
index 92003e11..a4573972 100644
--- a/misc/mke2fs.c
+++ b/misc/mke2fs.c
@@ -2603,6 +2603,17 @@ profile_error:
 		exit(1);
 	}
 
+	/*
+	 * Warn the user that filesystems with 128-byte inodes will
+	 * not work properly beyond 2038.  This can be suppressed via
+	 * a boolean in the mke2fs.conf file, and we will disable this
+	 * warning for file systems created for the GNU Hurd.
+	 */
+	if (inode_size == EXT2_GOOD_OLD_INODE_SIZE &&
+	    get_bool_from_profile(fs_types, "warn_y2038_dates", 1))
+		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;
diff --git a/misc/mke2fs.conf.5.in b/misc/mke2fs.conf.5.in
index 08bb9488..0b570303 100644
--- a/misc/mke2fs.conf.5.in
+++ b/misc/mke2fs.conf.5.in
@@ -505,6 +505,13 @@ This relation specifies the base file name for the huge files.
 This relation specifies the (zero-padded) width of the field for the
 huge file number.
 .TP
+.I warn_y2038_dates
+This boolean relation specifies wheather mke2fs will issue a warning
+when creating a file system with 128 byte inodes (and so therefore will
+not support dates after January 19th, 2038).  The default value is true,
+except for file systems created for the GNU Hurd since it only supports
+128-byte inodes.
+.TP
 .I zero_hugefiles
 This boolean relation specifies whether or not zero blocks will be
 written to the hugefiles while
diff --git a/misc/mke2fs.conf.in b/misc/mke2fs.conf.in
index 01e35cf8..05680992 100644
--- a/misc/mke2fs.conf.in
+++ b/misc/mke2fs.conf.in
@@ -12,16 +12,13 @@
 	}
 	ext4 = {
 		features = has_journal,extent,huge_file,flex_bg,metadata_csum,64bit,dir_nlink,extra_isize
-		inode_size = 256
 	}
 	small = {
 		blocksize = 1024
-		inode_size = 128
 		inode_ratio = 4096
 	}
 	floppy = {
 		blocksize = 1024
-		inode_size = 128
 		inode_ratio = 8192
 	}
 	big = {
@@ -44,4 +41,5 @@
 	hurd = {
 	     blocksize = 4096
 	     inode_size = 128
+	     warn_y2038_dates = 0
 	}
-- 
2.31.0