Hi all, This series fixes numerous flag handling bugs in the rmapbt key code. The most serious transgression is that key comparisons completely strip out all flag bits from rm_offset, including the ones that participate in record lookups. The second problem is that for years we've been letting the unwritten flag (which is an attribute of a specific record and not part of the record key) escape from leaf records into key records. The solution to the second problem is to filter attribute flags when creating keys from records, and the solution to the first problem is to preserve *only* the flags used for key lookups. The ATTR and BMBT flags are a part of the lookup key, and the UNWRITTEN flag is a record attribute. This has worked for years without generating user complaints because ATTR and BMBT extents cannot be shared, so key comparisons succeed solely on rm_startblock. Only file data fork extents can be shared, and those records never set any of the three flag bits, so comparisons that dig into rm_owner and rm_offset work just fine. A filesystem written with an unpatched kernel and mounted on a patched kernel will work correctly because the ATTR/BMBT flags have been conveyed into keys correctly all along, and we still ignore the UNWRITTEN flag in any key record. This was what doomed my previous attempt to correct this problem in 2019. A filesystem written with a patched kernel and mounted on an unpatched kernel will also work correctly because unpatched kernels ignore all flags. With this patchset applied, the scrub code gains the ability to detect rmap btrees with incorrectly set attr and bmbt flags in the key records. After three years of testing, I haven't encountered any problems. Online scrub is amended to recommend rebuilding of rmap btrees with the unwritten flag set in key records. The xfsprogs counterpart to this series amends xfs_repair to report key records with the unwritten flag bit set, just prior to rebuilding the rmapbt. It also exposes the bit via xfs_db to enable testing back and forth. If you're going to start using this mess, you probably ought to just pull from my git trees, which are linked below. This is an extraordinary way to destroy everything. Enjoy! Comments and questions are, as always, welcome. --D kernel git tree: https://git.kernel.org/cgit/linux/kernel/git/djwong/xfs-linux.git/log/?h=rmap-btree-fix-key-handling xfsprogs git tree: https://git.kernel.org/cgit/linux/kernel/git/djwong/xfsprogs-dev.git/log/?h=rmap-btree-fix-key-handling --- db/btblock.c | 4 +++ libxfs/xfs_rmap_btree.c | 40 ++++++++++++++++++++++++------- repair/scan.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++- 3 files changed, 93 insertions(+), 11 deletions(-)
