[PATCH v2 0/6] btrfs-progs: introduce "btrfs rescue fix-data-checksum"

[Qu Wenruo <wqu@suse.com>]

[CHANGELOG]
v2:
- Rename the subcommand to "fix-data-checksum"
  It's better to use full name in the command name

- Remove unused members inside corrupted_block
  The old @extent_bytenr and @extent_len is no longer needed, even for
  the future file-deletion action.

- Fix the bitmap size off-by-1 bug
  We must use the bit 0 to represent mirror 1, or the bitmap size will
  exceed num_mirrors.

- Introduce -i|--interactive mode
  Will ask the user for the action on the corrupted block, including:

  * Ignore
    The default behavior if no command is provided

  * Use specified mirror to update the data checksum item
    The user must input a number inside range [1, num_mirrors].

- Introduce -m|--mirror <num> mode
  Use specified mirror for all corrupted blocks.
  The value <num> must be >= 1. And if the value is larger than the
  actual max mirror number, the real mirror number will be
  `num % (num_mirror + 1)`.

We have a long history of data csum mismatch, caused by direct IO and
buffered being modified during writeback.

Although the problem is worked around in v6.15 (and being backported),
for the affected fs there is no good way to fix them, other than complex
manually find out which files are affected and delete them.

This series introduce the initial implementation of "btrfs rescue
fix-data-checksum", which is designed to fix such problem by either:

- Update the csum items using the data from specified copy

The subcommand has 3 modes so far:

- Readonly mode
  Only report all corrupted blocks and affected files, no repair is
  done.

- Interactive mode
  Ask for what to do, including

  * Ignore (the default)
  * Use certain mirror to update the checksum item

- Mirror mode
  Use specified mirror to update the checksum item, the batch mode of
  the interactive one.

In the future, there will be one more mode:

- Delete mode
  Delete all involved files.

  There are still some points to address before implementing this mode.

Qu Wenruo (6):
  btrfs-progs: introduce "btrfs rescue fix-data-checksum"
  btrfs-progs: fix a bug in btrfs_find_item()
  btrfs-progs: fix-data-checksum: show affected files
  btrfs-progs: fix-data-checksum: introduce interactive mode
  btrfs-progs: fix-data-checksum: update csum items to fix csum mismatch
  btrfs-progs: fix-data-checksum: introduce -m|--mirror option

 Documentation/btrfs-rescue.rst  |  28 ++
 Makefile                        |   2 +-
 cmds/rescue-fix-data-checksum.c | 511 ++++++++++++++++++++++++++++++++
 cmds/rescue.c                   |  65 ++++
 cmds/rescue.h                   |  10 +
 kernel-shared/ctree.c           |  17 +-
 kernel-shared/file-item.c       |   2 +-
 kernel-shared/file-item.h       |   5 +
 8 files changed, 635 insertions(+), 5 deletions(-)
 create mode 100644 cmds/rescue-fix-data-checksum.c

--
2.49.0