Re: [RFC PATCH 0/2] wic: warn on usage of Y2038 affected file systems

[Anton Mikanovich <amikan@ilbers.de>]

01.02.2021 21:58, florian.bezdeka@siemens.com wrote:
> From: Florian Bezdeka <florian.bezdeka@siemens.com>
>
> Hi ISAR developers,
>
> this series is the summary of a nice journey through the file system
> jungle regarding Y2038 problem. It all began with a warning which is
> reported by kernels >= 5.4:
>
> ext4 filesystem being mounted at (mountpoint) supports timestamps until
> 2038 (0x7fffffff)
>
> I guess that most ISAR layers are using the Debian kernels, so that
> warning was not recognized yet or at least not very often.
>
> When reading this warning I was surprised. Shouldn't a modern file
> system like ext4 be Y2038-safe? As it turned out it depends on the
> inode size if an ext4 file system is safe or not. So why was the
> inode size not sufficient in my case?
>
> The inode size is chosen during file system generation and depends on
> the size of the file system that is going to be created. For details
> let's have a look at `man mke2fs`:
>
> -T usage-type[,...]
>      Specify how the filesystem is going to be used, so that mke2fs can
>      choose optimal filesystem parameters for that use. The usage types
>      that are supported are defined in the configuration file
>      /etc/mke2fs.conf. The user may specify one or more usage types
>      using a comma separated list.
>
>      If this option is is not specified, mke2fs will pick a single
>      default usage type based on the size of the filesystem to be
>      created. If the filesystem size is less than 3 megabytes, mke2fs
>      will use the filesystem type floppy. If the filesystem size is
>      greater than or equal to 3 but less than 512 megabytes, mke2fs(8)
>      will use the filesystem type small.
>
> The relevant parts from /etc/mke2fs.conf:
> [fs_types]
> ...
>          small = {
>                  blocksize = 1024
>                  inode_size = 128
>                  inode_ratio = 4096
>          }
> ...
>
> So whenever you create an ext4 file system with less than 512MB in
> size you will end up with 128 byte inodes and your file system is
> not Y2038-safe.
>
> The ISAR part:
> ext4 may often be used in combination with the expand-on-first-boot
> recipe / feature. So whenever creating a small partition (e.g. inside
> a wic file) and extending it later may result in a Y2038 affected ext4
> file system.
>
> That is exactly what happened to me and I would like to make sure that
> all other ISAR users are aware of this situation.
>
> Valid workarounds found so far:
>   - Tell wic that an partition will grow:
>     Add `--mkfs-extraopts "-T ext4"` to your wic partition definition
>   - Set the inode size to 256 (for small ext4 partitions)
>     Add `--mkfs-extraopts "-I 256"` to your wic partition definition
>
> The upstream part:
> None of the following patches has been sent to any upstream (OE)
> mailing lists yet but hopefully that will happen soon. So far: Any
> comments welcome!
>
> Best regards,
> Florian
>
> Florian Bezdeka (2):
>    wic-img: Forward warnings from wic to bitbake
>    wic: Warn if an ext filesystem affected by the Y2038 problem is used
>
>   meta/classes/wic-img.bbclass | 20 ++++++++++++++-----
>   scripts/lib/wic/partition.py | 38 ++++++++++++++++++++++++++++++++++++
>   2 files changed, 53 insertions(+), 5 deletions(-)
>
Applied to next, thanks.

-- 
Anton Mikanovich
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