Date:   Fri, 13 Aug 2021 11:14:36 -0700
From:   "Darrick J. Wong" <djwong@...nel.org>
To:     Theodore Ts'o <tytso@....edu>
Cc:     Andreas Dilger <adilger@...ger.ca>,
        linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH v2] mke2fs: warn about missing y2038 support when
 formatting fresh ext4 fs

On Fri, Aug 13, 2021 at 01:52:00PM -0400, Theodore Ts'o wrote:
> On Thu, Aug 12, 2021 at 04:22:22PM -0700, Darrick J. Wong wrote:
> > 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.
> 
> So I took a closer look, and it turns out that we changed the default
> inode size for ext2 and ext3 file systems in 2008 (see commit
> b1631cce648e ("Create new filesystems with 256-byte inodes by
> default"), in e2fsprogs 1.40.4.  Even a positively antedeluvian distro
> such as RHEL 7 uses e2fsprogs 1.42.9, and RHEL 6 EOL'ed November 30th,
> 2020.
> 
> There were only two cases where we created file systems with 128 byte
> inodes --- "small" and "floppy" sized file systems, and for the GNU
> Hurd, which only supports the original 128 byte inode.  What will GNU
> Hurd do in 16.5 years?  ¯\_(ツ)_/¯

Perhaps in that time someone can donate a disused Opteron 140 system?
Assuming the motherboard capacitors haven't since lost their mojo.

> Given that, I think we can simplify the patch a little, and just use a
> mke2fs.conf boolean to disable the warning message.
> 
> What do folks think?
> 
> 						- Ted
> 
> 
> 
> commit f569fe86caddf964973ed35cdf36ed520ef23a0c
> Author: Darrick J. Wong <djwong@...nel.org>
> Date:   Thu Aug 12 16:22:22 2021 -0700
> 
>     mke2fs: warn about missing y2038 support when formatting fresh ext4 fs
>     
>     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. ]

Even better!

>     
>     Signed-off-by: Darrick J. Wong <djwong@...nel.org>
>     Signed-off-by: Theodore Ts'o <tytso@....edu>
> 
> diff --git a/misc/mke2fs.c b/misc/mke2fs.c
> index 92003e11..881ffd31 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 ext2, ext3, and hurd file systems.

Um... the conffile changes only disable the warning for 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..62d0fdb5 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,

Nit: need a closing parentheses after '2038' or no opening paren.

> +except for file systems created for the GNU Hurd, which does not support
> +inodes larger than 128 bytes.

I wonder if this statementt about Hurd this belongs in the conffile as a
comment in the hurd section?

--D

> +.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
>  	}

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