[PATCH v2 0/7] btrfs-progs: csum-change: add the initial support for offline csum type change

[Qu Wenruo <wqu@suse.com>]

[CHANGELOG]
v2:
- Skip csum item checks if the fs is under csum change
  Tree-checker can be too sensitive if the csum size doesn not match the
  old csum size, which can lead to false alerts on overlapping csum
  items.

  But we still want the tree checker functionality overall, so just
  disable csum item related checks for csum change.

[DESIGN]
The csum change workflow looks like this:

- Generate new data csums
  New data csums would have a different objectid (CSUM_CHANGE -13),
  other than the existing one (EXTENT_CSUM -10).

  The generation part would also verify the data contents, if any
  mismatch we would error out.

- Delete the old data csums

- Change data csums objectid

- Rewrite metadata csums in-place
  At this stage, we would check the checksum for both old and new algo.
  If the metadata matches the old csum, we rewrite using new csum.
  If the metadata matches the new csum, we skip it.
  If the metadata doesn't match either csum, we error out.

[TESTS]
For now it's only basically tested manually.

So far the result looks good, the result fs can pass "btrfs check
--check-data-csum".

[TODO]
- Support for resume
  Currently we won't resume an interrupted csum conversion.
  Although the design should be able to handle any interruption at data
  csum conversion part, and as long as metadata csum writes are atomic,
  the metadata rewrites should also be fine.

- Support for revert if errors are found
  If we hit data csum mismatch and can not repair from any copy, then
  we should revert back to the old csum.

- Suppot for precaustious metadata check
  We'd better read and very metadata before rewriting them.

- Extra test cases


Qu Wenruo (7):
  btrfs-progs: tune: rework the main idea of csum change
  btrfs-progs: tune: implement the prerequisite checks for csum change
  btrfs-progs: tune: add the ability to read and verify the data before
    generating new checksum
  btrfs-progs: tune: add the ability to generate new data checksums
  btrfs-progs: tune: add the ability to delete old data csums
  btrfs-progs: tune: add the ability to migrate the temporary csum items
    to regular csum items
  btrfs-progs: tune: add the ability to change metadata csums

 check/mode-common.c             |   11 +-
 convert/main.c                  |   12 +-
 kernel-shared/ctree.c           |    3 -
 kernel-shared/ctree.h           |   19 +-
 kernel-shared/disk-io.c         |    8 -
 kernel-shared/file-item.c       |   46 +-
 kernel-shared/file-item.h       |    4 +-
 kernel-shared/print-tree.c      |   11 +-
 kernel-shared/tree-checker.c    |    5 +
 kernel-shared/uapi/btrfs_tree.h |    1 +
 mkfs/rootdir.c                  |   11 +-
 tune/change-csum.c              | 1053 +++++++++++++++++--------------
 tune/main.c                     |    2 +-
 tune/tune.h                     |    3 +-
 14 files changed, 646 insertions(+), 543 deletions(-)

-- 
2.40.1