[Bug 1844012] Re: grub2 doesn't recognize ext4 with metadata_csum_seed enabled

[Adrien Beau]

Note that this is not limited to metadata_csum_seed, other "recently"
added ext4 features cannot be used on the system partition (and maybe
the whole system disk, if you have other ext4 partitions there with such
features).

At least confirmed to not work with GRUB:

- metadata_csum_seed
- ea_inode
- large_dir
- casefold

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Title:
  grub2 doesn't recognize ext4 with metadata_csum_seed enabled

Status in grub2 package in Ubuntu:
  Confirmed
Status in grub2 package in Debian:
  Unknown

Bug description:
  /usr/lib/grub/x86_64-efi/ext2.mod, from:

  grub-efi-amd64-bin:
    Installed: 2.02-2ubuntu8.13
    Candidate: 2.02-2ubuntu8.13

  doesn't recognize an ext4 filesystem with metadata_csum_seed set.

  This is true in command-line grub, not just the update-grub software.
  Attempting

  linux (hdx,gptx)/ etc

  on an ext4 fs with metadata_csum enabled fails; removing the
  metadata_csum_seed option fixes this.

  The failure is "unknown filesystem" for any ext4 fs with
  metadata_csum_seed set. Apparently saving the metadata checksum seed
  in the superblock changes it beyond recognition for grub.

   The message appears to be coming from 
  grub-2.04/grub-core/kern /fs.c:

  grub_fs_t
  grub_fs_probe (grub_device_t device)
  {....
   grub_error (GRUB_ERR_UNKNOWN_FS, N_("unknown filesystem"));
  }
  which appears to probe for filesystems by calling the fs modules to attempt to mount it.

  
  I tried to install latest grub from eaon to see if upstream has fixed this, but it depended on too much other unreleased software such as libc6.

  I pulled the 2.04 source. There is nothing in the Changelog that
  appears to address this.

  
  from `man ext4`:
   metadata_csum_seed
                This feature allows the filesystem to store the metadata checksum seed in the superblock, which allows the administrator to change the UUID of a filesystem using the metadata_csum feature while it is mounted.

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