Fix data loss on writes larger than the tape block size#607
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_unified_insert_new_request copies at most one cache block (the tape block size) but returned the full requested count, so the append loop in unified_write advanced past data that was never stored. Writes larger than the block size silently lost everything after the first block while reporting success. Latent with libfuse 2, which caps requests at 128 KiB, below the default 512 KiB block; reachable today through the I/O scheduler API and triggered by FUSE 3 request sizes. Return the number of bytes actually stored. A regression test (multi-block single writes of random data, content verified) accompanies the integration test suite. Fixes LinearTapeFileSystem#591
This was referenced Jun 12, 2026
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_unified_insert_new_requestin the unified I/O scheduler copies at most one tape block of an incoming write into the new request, but reports the full count as written. Any singlewrite()larger than the tape block size is silently truncated to one block — a 1 MiB write with the default 512 KiB block size stores exactly 524288 bytes while the application sees success.One commit, 5 lines: cap the reported count at what was actually queued, so the caller loops over the remainder.
This matches the corruption reported in #591. A regression test that verifies the content of multi-block single writes ships with the integration test-suite PR (#611,
t/13-large-write-integrity.sh).Note: #603 (FUSE 3) includes this same commit, because FUSE 3's 1 MiB requests expose the bug in the default configuration; git drops the duplicate whichever PR merges first.
Fixes #591.