[Bug 1601997] Re: Ubuntu 16.10 installer sets metadata_csum option on ext4 partition which is incompatible with other LTS Ubuntu versions

[Theodore Ts'o]

One bit of context --- metadata_csum is not enabled by default in the
official upstream e2fsprogs.tar.gz file.  So with my upstream maintainer
hat, I deliberately decided not to enable it by default, and mentioned
in the release notes that individual distributions should decide whether
they wanted to enable it.   So with the upstream e2fsprogs tarball, the
user can still request metadata_csum by asking for it explicitly: mke2fs
-t ext4 -O metadata_csum.

With my *Debian* maintainer hat on (well, with some egging on with my
upstream maintainer persona :-), I decided to enable metadata_csum by
default so that in the testing and unstable branches, metadadata_csum
checking would get some additional exposure, and hence testing.  This
gambit has worked.  There have been a number of bug between 1.43 and
1.43.3 that were fixed because they were reported by Debian users.
Whether I will continue leaving metadata_csum enabled right before
Debian Stretch goes into final lockdown for the Debian Stable release is
not something I have decided, but so far the bug report rate has been
positive.

Ubuntu has apparently adopted the Debian enablement of metadata_csum by
default, because it's based on the Debian 1.43.3-1 package.   However,
there may be some differences between Ubuntu and Debian --- the average
technical sophistication of a Debian vs. a Ubuntu user, compatibility
constraints with Ubuntu LTS, etc. --- that may drive a different
decision with respect to mke2fs's *defaults*.

It would be good if a decision is made explicitly by Ubuntu / Canonical
to decide what best makes since for Ubuntu.  If you decide that Ubuntu
16.10 is a community distro, and you want to help me test metadata_csum,
that's great.    I have had some experiences with less-than-savvy Ubuntu
users who really struggled with filing a useful bug report and
participating in root causing a bug.

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https://bugs.launchpad.net/bugs/1601997

Title:
  Ubuntu 16.10 installer sets metadata_csum option on ext4 partition
  which is incompatible with other LTS Ubuntu versions

Status in e2fsprogs package in Ubuntu:
  Invalid

Bug description:
  Ubuntu 16.10 installer sets metadata_csum option on ext4 partition
  which is incompatible with other LTS Ubuntu versions (12.04 LTS, 14.04
  LTS, 16.04 LTS).

  Steps to reproduce:
  1. Download Ubuntu 16.10 installation media.
  2. Install Ubuntu.
  3. Try to do fsck -fy /dev/sdX1 from other supported Ubuntu distro.

  Expected results:
  User can check and fix errors on ext4 filesystem, created on Ubuntu 16.10.

  Actual results:
  User can not check and fix errors on ext4 filesystem because of lack of 'metadata_csum' option in previous LTS Ubuntu versions.
  The only one working solution was to scan from 16.10 live install media.

  Note:
  it is known, that Dan Watkins disabled metadata_csum when creating ext4 filesystems ( see http://bazaar.launchpad.net/~daniel-thewatkins/maas-images/fix-yakkety-builds/revision/305 ). It is good solution.

  ProblemType: Bug
  DistroRelease: Ubuntu 16.10
  Package: e2fsprogs 1.43.1-1
  ProcVersionSignature: Ubuntu 4.4.0-30.49-generic 4.4.13
  Uname: Linux 4.4.0-30-generic i686
  ApportVersion: 2.20.2-0ubuntu1
  Architecture: i386
  CurrentDesktop: Unity
  Date: Mon Jul 11 23:42:49 2016
  SourcePackage: e2fsprogs
  UpgradeStatus: No upgrade log present (probably fresh install)

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