linux-ext4 - Re: "beyond 2038" warnings from loopback mount is noisy

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Date:   Tue, 03 Sep 2019 17:13:38 -0400
From:   Qian Cai <cai@....pw>
To:     Arnd Bergmann <arnd@...db.de>, Andreas Dilger <adilger@...ger.ca>
Cc:     Deepa Dinamani <deepa.kernel@...il.com>,
        Jeff Layton <jlayton@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Theodore Ts'o <tytso@....edu>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: "beyond 2038" warnings from loopback mount is noisy

On Tue, 2019-09-03 at 21:50 +0200, Arnd Bergmann wrote:
> On Tue, Sep 3, 2019 at 9:39 PM Andreas Dilger <adilger@...ger.ca> wrote:
> > 
> > On Sep 3, 2019, at 12:15 PM, Qian Cai <cai@....pw> wrote:
> > > 
> > > On Tue, 2019-09-03 at 09:36 -0700, Deepa Dinamani wrote:
> > > > We might also want to consider updating the file system the LTP is
> > > > being run on here.
> > > 
> > > It simply format (mkfs.ext4) a loop back device on ext4 with the kernel.
> > > 
> > > CONFIG_EXT4_FS=m
> > > # CONFIG_EXT4_USE_FOR_EXT2 is not set
> > > # CONFIG_EXT4_FS_POSIX_ACL is not set
> > > # CONFIG_EXT4_FS_SECURITY is not set
> > > # CONFIG_EXT4_DEBUG is not set
> > > 
> > > using e2fsprogs-1.44.6. Do you mean people now need to update the kernel
> > > to
> > > enable additional config to avoid the spam of warnings now?
> > 
> > Strange.  The defaults for mkfs.ext4 _should_ default to use options that
> > allow enough space for the extra timestamps.
> > 
> > Can you please provide "dumpe2fs -h" output for your filesystem, and the
> > formatting options that you used when creating this filesystem.
> 
> According to the man page,
> 
>         "The default inode size is controlled by the mke2fs.conf(5)
> file.  In the
>          mke2fs.conf file shipped with  e2fsprogs, the default inode size is
> 256
>          bytes for most file systems, except for small file systems
> where the inode
>          size will be 128 bytes."
> 
> If this (small file systems) is the problem, then I think we need to
> do two things:
> 
> 1. Change the per-inode warning to not warn if the inode size for the
>     file system is less than 256. We already get a mount-time warning
>     in that case.
> 
> 2. Change the mkfs.ext4 defaults to never pick a 128 byte inode unless
>     the user really wants this (maybe not even then).

Indeed.

# dd if=/dev/zero of=small bs=1M count=50
50+0 records in
50+0 records out
52428800 bytes (52 MB, 50 MiB) copied, 0.0168322 s, 3.1 GB/s

# losetup -f small

# mkfs.ext4 /dev/loop0

# dumpe2fs -h /dev/loop0 
dumpe2fs 1.44.6 (5-Mar-2019)
Filesystem volume name:   <none>
Last mounted on:          <not available>
Filesystem UUID:          8cd1b7f1-dec9-45fc-807b-26cceedcdaa7
Filesystem magic number:  0xEF53
Filesystem revision #:    1 (dynamic)
Filesystem features:      has_journal ext_attr resize_inode dir_index filetype
extent 64bit flex_bg sparse_super large_file huge_file dir_nlink extra_isize
metadata_csum
Filesystem flags:         unsigned_directory_hash 
Default mount options:    user_xattr acl
Filesystem state:         clean
Errors behavior:          Continue
Filesystem OS type:       Linux
Inode count:              12824
Block count:              51200
Reserved block count:     2560
Free blocks:              44440
Free inodes:              12813
First block:              1
Block size:               1024
Fragment size:            1024
Group descriptor size:    64
Reserved GDT blocks:      256
Blocks per group:         8192
Fragments per group:      8192
Inodes per group:         1832
Inode blocks per group:   229
Flex block group size:    16
Filesystem created:       Tue Sep  3 16:10:35 2019
Last mount time:          Tue Sep  3 16:10:42 2019
Last write time:          Tue Sep  3 16:10:48 2019
Mount count:              1
Maximum mount count:      -1
Last checked:             Tue Sep  3 16:10:35 2019
Check interval:           0 (<none>)
Lifetime writes:          6050 kB
Reserved blocks uid:      0 (user root)
Reserved blocks gid:      0 (group root)
First inode:              11
Inode size:	          128
Journal inode:            8
Default directory hash:   half_md4
Directory Hash Seed:      6507a815-ee3a-4573-99c8-2f9103061dec
Journal backup:           inode blocks
Checksum type:            crc32c
Checksum:                 0x4b0ec46e
Journal features:         journal_64bit journal_checksum_v3
Journal size:             4096k
Journal length:           4096
Journal sequence:         0x00000004
Journal start:            0
Journal checksum type:    crc32c
Journal checksum:         0x23f8be20