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Matthew Jackson
6e14fc0c0c
Security - Remove the unsafe Vec::set_len over recycled sector buffers — UB reachable from safe code (GHSA-j8ww-f5fg-9pmh, low). Uses Vec::resize; pooling unchanged. CI / tooling - clippy on stable with the MSRV single-sourced from Cargo.toml; cargo-deny dependency-audit gate with first-party git sources allowed (#15); audience-based comment-guard (#17). Docs - README (keydb ownership, BD-J parser count), drive-access transport/reset notes, mux timeline module-doc links.
30 lines
1.3 KiB
Markdown
30 lines
1.3 KiB
Markdown
# file_sector_source::macos
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macOS has no direct `POSIX_FADV_SEQUENTIAL` equivalent; the idiomatic hint is
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`fcntl(F_RDADVISE, &radvisory)` describing the byte range you intend to read
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soon. The open-time sequential hint points it at the whole file (clamped to
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`RDADVISE_MAX_BYTES` so a multi-TB ISO doesn't ask the kernel to prefetch
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everything at once).
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## RDADVISE_MAX_BYTES
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Cap on the byte length passed to `F_RDADVISE`. Asking for a multi-GB
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readahead window is counterproductive — the OS doesn't have that much cache
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to throw at one fd. 64 MiB is generous for our use case (sweep, mux) so the
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kernel's prefetch keeps pace with our app-level pipeline depth.
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## drop_window
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macOS has no direct `POSIX_FADV_DONTNEED` equivalent for a byte range.
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`fcntl(F_NOCACHE)` would disable caching globally on the fd (too coarse — we
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want the unread region to still benefit). Best approximation: no-op.
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macOS's unified buffer cache is generally less prone to the pin-everything
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pathology that triggers the regression on Linux NFS clients.
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## prefetch
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Async-prefetch the byte range `[offset, offset+len)`. macOS uses the same
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`fcntl(F_RDADVISE, &radvisory)` primitive as the open-time sequential hint,
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just targeted at a moving window instead of the whole file. The kernel
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queues I/O for the requested range and returns immediately.
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