docs: audit io_uring fixed-buffer registration invariants#4022
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Add an invariants-table audit of `RegisteredBufferGroup` covering registration timing, silent fallback to unfixed opcodes, page-pinning ownership, default sizing vs kernel limits, drop ordering, and kernel cleanup on ring fd close. Each invariant cites a single file:line location with an OK / GAP / UNKNOWN status verdict. The one GAP - `IoUringWriter::with_ring` ignoring the configured `register_buffers` flag - is left to a follow-up PR with a scoped plumbing fix described inline.
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This was referenced May 14, 2026
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…ern (#4320) The post-#4310 tests.rs at 882 lines exceeded the 650-line cap. Split into a tests/ directory grouped by concern, each file well under cap: - tests/mod.rs (39) - shared try_ring / try_group helpers and module decls. - tests/registry.rs (113) - page size, validation guards, slot allocator. - tests/submit.rs (179) - submit_read/write_fixed_batch helpers. - tests/stats.rs (141) - acquire/miss counters and snapshot semantics. - tests/status.rs (49) - try_new_with_status outcome reporting. - tests/drop_contract.rs (309) - Drop semantics and constrained-env coverage for the PR #4022 / task #2118 fixed-buffer invariants audit. The try_ring / try_group helpers replace the repeated match-or-return boilerplate that handled environments where io_uring is unavailable (CI sandboxes, seccomp, kernel < 5.6). No behavioural change; test coverage is preserved.
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May 18, 2026
Add an invariants-table audit of `RegisteredBufferGroup` covering registration timing, silent fallback to unfixed opcodes, page-pinning ownership, default sizing vs kernel limits, drop ordering, and kernel cleanup on ring fd close. Each invariant cites a single file:line location with an OK / GAP / UNKNOWN status verdict. The one GAP - `IoUringWriter::with_ring` ignoring the configured `register_buffers` flag - is left to a follow-up PR with a scoped plumbing fix described inline.
oferchen
added a commit
that referenced
this pull request
May 18, 2026
…ern (#4320) The post-#4310 tests.rs at 882 lines exceeded the 650-line cap. Split into a tests/ directory grouped by concern, each file well under cap: - tests/mod.rs (39) - shared try_ring / try_group helpers and module decls. - tests/registry.rs (113) - page size, validation guards, slot allocator. - tests/submit.rs (179) - submit_read/write_fixed_batch helpers. - tests/stats.rs (141) - acquire/miss counters and snapshot semantics. - tests/status.rs (49) - try_new_with_status outcome reporting. - tests/drop_contract.rs (309) - Drop semantics and constrained-env coverage for the PR #4022 / task #2118 fixed-buffer invariants audit. The try_ring / try_group helpers replace the repeated match-or-return boilerplate that handled environments where io_uring is unavailable (CI sandboxes, seccomp, kernel < 5.6). No behavioural change; test coverage is preserved.
oferchen
added a commit
that referenced
this pull request
May 18, 2026
…ern (#4320) The post-#4310 tests.rs at 882 lines exceeded the 650-line cap. Split into a tests/ directory grouped by concern, each file well under cap: - tests/mod.rs (39) - shared try_ring / try_group helpers and module decls. - tests/registry.rs (113) - page size, validation guards, slot allocator. - tests/submit.rs (179) - submit_read/write_fixed_batch helpers. - tests/stats.rs (141) - acquire/miss counters and snapshot semantics. - tests/status.rs (49) - try_new_with_status outcome reporting. - tests/drop_contract.rs (309) - Drop semantics and constrained-env coverage for the PR #4022 / task #2118 fixed-buffer invariants audit. The try_ring / try_group helpers replace the repeated match-or-return boilerplate that handled environments where io_uring is unavailable (CI sandboxes, seccomp, kernel < 5.6). No behavioural change; test coverage is preserved.
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Summary
docs/audits/io-uring-fixed-buffer-invariants-audit.mdcovering the operational invariants ofRegisteredBufferGroupatcrates/fast_io/src/io_uring/registered_buffers.rs.IORING_OP_READ/IORING_OP_WRITE, page-pinning for the ring's lifetime, default sizing vs kernel limits, drop ordering, and kernel-side unregister on ring fd close - to a singlefile:linecitation with an OK / GAP / UNKNOWN status verdict.IoUringWriter::with_ringatcrates/fast_io/src/io_uring/file_writer.rs:118ignoresIoUringConfig::register_buffersand hard-codescount = 8. A scoped plumbing fix is described inline; left to a separate follow-up PR.BgidAllocatorwork (task Remove outdated golden CLI version test #2044), provided-buffer-ring footprint (task Fix clippy warning in sparse executor test #1936), and engine local-copy buffer pool (task Align cross-compile matrix with build_daemon metadata #2045) audits.Tracking issue: #2118. This audit complements the three existing siblings (
io-uring-fixed-buffer-audit.md,io-uring-fixed-buffer-registration.md,iouring-fixed-buffer-registration.md) by collapsing the findings into a single invariants checklist rather than narrative form.Docs-only PR. No code changes.
Test plan
file:linecitation against the current tree (paths and line numbers verified at audit time; no code moved in this PR).