[Bug 2044657] Re: zfs block cloning file system corruption

[Rob N]

Hi all,

Patch for 0.8 (and others) available here:
https://zfsonlinux.topicbox.com/groups/zfs-
discuss/T12876116b8607cdb/lseek-glitch-dirty-dnode-patches-for-older-
openzfs-zfs-on-linux

If you didn't want to take all of 2.2.2 or 2.1.14, specific patches for
those series are:

https://github.com/robn/zfs/commits/dnode-dirty-data-2.2
https://github.com/robn/zfs/commits/dnode-dirty-data-2.1

Block cloning appears unrelated at this point, though there are multiple
cloning-related fixes in 2.2.2, and more on master that (presumably)
will land in 2.2.3.

Regarding cloning being "off by default" in 2.2.1, it will still appear
"enabled" in the feature list because it is actually enabled in the disk
structures. The new module option `zfs_bclone_enabled` is disabled (0)
by default, and when disabled it rejects the syscalls that lead cloning
to happen. So eg `cp --reflink=always` would return `ENOTSUPP`.

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https://bugs.launchpad.net/bugs/2044657

Title:
  zfs block cloning file system corruption

Status in linux-hwe-6.2 package in Ubuntu:
  Confirmed
Status in linux-hwe-6.5 package in Ubuntu:
  Confirmed
Status in zfs-linux package in Ubuntu:
  Confirmed

Bug description:
  OpenZFS 2.2 reportedly has a bug where block cloning might lead to
  file system corruption and data loss. This was fixed in OpenZFS 2.2.1.

  Original bug report: https://github.com/openzfs/zfs/issues/15526

  and 2.2.1 release notes:
  https://github.com/openzfs/zfs/releases/tag/zfs-2.2.1

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