file_scan: block-aligned block-count estimate, clearer hole names (#89 review) - #94
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…review) Follow-up to the sparse-hole-skip work in #89, addressing crass's review comments on that PR. allocate_hashes() sized the block array from sum(fe_length)/blocksize + 1. FIEMAP extents are aligned to the filesystem block size (~4K), not to oans blocksize (128K default), so an extent can start and end mid-block and a partially-overlapped block is still read and hashed. The old estimate could therefore under-count by up to ~2 blocks per mapped extent, tripping the one-at-a-time realloc growth in add_block_hash() on fragmented files. Round each extent out to block boundaries before summing so the estimate never under-counts; adjacent extents sharing a block can over-count, but erring high only wastes a little memory once, so it is the safe bias for a preallocation. Also rename hole_run_at() -> hole_run_length() and the local `hole` -> `hole_length`: both name a byte length, not a position. No behavioural change to hashing or dedupe; verify.sh green (90 tests + valgrind smoke). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Follow-up addressing @crass's review comments on #89 (sparse-hole-skip), now merged.
What
Block-count estimate no longer under-counts (
allocate_hashes). The oldcode sized the block array from
sum(fe_length) / blocksize + 1. FIEMAPextents are aligned to the filesystem block size (~4K), not to oans
blocksize(128K default), so an extent can start and end mid-block and apartially-overlapped block is still read and hashed. The estimate could
under-count by up to ~2 blocks per mapped extent, tripping the
one-at-a-time
reallocgrowth inadd_block_hash()on fragmented files.Each extent is now rounded out to oans-block boundaries before summing, so
the estimate never under-counts. Adjacent extents sharing a block can
over-count, but erring high only wastes a little memory once — the safe bias
for a preallocation. (crass's suggestion.)
Naming:
hole_run_at()→hole_run_length()and the localhole→hole_length. Both name a byte length, not a position.Not a bug fix
Correctness was never affected —
add_block_hash()already grows the arraywhen the estimate is short, so no hash or dedupe result changes. This just
avoids the realloc churn and reads more clearly.
Testing
scripts/verify.shgreen: build clean, 90 tests pass (incl. the sparse-filesuite), valgrind scan+dedupe+replay smoke clean.
🤖 Generated with Claude Code