docs: warn FIEMAP locations are unstable#693
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Merged — cherry-picked onto master, authorship preserved. Thanks! |
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Summary
Document that FIEMAP/filefrag extent locations on bcachefs are observations, not a stable userspace write ABI.
This addresses the safety question from koverstreet/bcachefs#774: even with a preallocated file or
nocow, userspace should not write directly to the reported block device offsets while the filesystem is mounted, because bcachefs may move extents in the background and userspace cannot lock those moves out.The supported direction for swapfile-style block I/O is filesystem-coordinated handling, not a manually constructed device-mapper table. The active swapfile work is #646, related to koverstreet/bcachefs#368.
Testing
git diff --checkpython3 -m py_compile doc/macro2rst.pyrst2man --halt=2 doc/bcachefs.5.rst.tmpl /tmp/bcachefs.5.rst.tmpl.manRelated