[PATCH 0/2] btrfs-progs: rely on "btrfstune --csum" to replace "btrfs check --init-csum-tree"

[Qu Wenruo <wqu@suse.com>]

We had a report that "btrfs check --init-csum-tree" corrupted a
seemingly fine btrfs (which can originally pass "btrfs check
--readonly").

The root cause is in how we rebuild the csum tree, in the btrfs check
code, we screw up the csum tree root, then rely on the extent tree
repair code to finish the damage we introduced.

This can lead to unexpected corner cases, if the fs is already fine,
there is no need for such risky move.

Considering there are valid ways to cause data csum mismatch (mostly
O_DIRECT and modifying the buffer when it's still under writeback), some
users expect to use "btrfs check --init-csum-tree" to fix the csum
mismatch, which can lead to the same corruption.

Instead this patchset would recommend the end users to go "btrfstune
--csum", as it is way less risky by its design, and no more damage to
the fs caused by ourselves.

I hope we can completely go that direction when the "btrfstune --csum"
option is moved out of experimental features.

Qu Wenruo (2):
  btrfs-progs: tune: allow --csum to rebuild csum tree
  btrfs-progs: check: add advice to avoid --init-csum-tree

 check/main.c       |  9 +++++++++
 tune/change-csum.c | 35 +++++++++++++++++++++++++----------
 tune/main.c        |  3 ++-
 3 files changed, 36 insertions(+), 11 deletions(-)

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2.41.0