Elamur Groupantsvfs-host
The groupant beside vfs/src/host.rs in the Mova repository: what the code computes, what it never does, how to go back from its outputs, its invariants, cost and checks.
Facts
Implementation material. A Mova code model describes this code at one source revision: partial models, finite checks and their stated scope. It is not a reviewed general exposition, and its labels are shown as written, never raised.
Components
| component | label | where |
|---|---|---|
| approximant | partial | approximant |
| ast | partial | syntax.json |
| composition | partial | composition |
| cost | partial | Cost |
| descriptant | present | descriptant |
| invariant | partial | Invariant |
| tests | executed bounded checks | tests |
Obernants
The typed relations around the forward model: the behaviour complement (what the code never does), the reverse reconstruction (every input compatible with an output) and specialised views.
| id | type | label | where |
|---|---|---|---|
behavior_complement | behavior_complement | partial source derived model | behavior_complement |
reverse_reconstruction | reverse_reconstruction | partial source derived model | reverse_reconstruction |
canonical_preflight | canonical_preflight | partial source derived model | canonical_preflight |
race_boundary | race_boundary | partial source derived model | race_boundary |
metadata_projection | metadata_projection | partial source derived model | metadata_projection |
temp_effects | temp_effects | partial source derived model | temp_effects |
Parts
Model text
descriptant
vfs-host
Confined DirFs and explicit unrestricted RealFs adapters.
Prospective epoch
2026-10-31: source reviewed before edits; prospective review retained under $MOVA_DATA/runs/octopus-wave31-vfs-2026-10-31/prospective.md. Predicted order/cost: O(path bytes+ancestor canonicalization syscalls) resolution; OS byte I/O costs; read_dir sort O(k log k), memory O(names+data). No measured speed claim.
Observation epoch
Bounded actual calls and compiled negative controls are recorded in tests.md. Production behavior bytes unchanged; only focused test blocks added. Snapshot constant-time wording is conditional on cwd and destruction; recursive operations may partially commit.
Unsupported approximants
No executable percentage surrogate is claimed for these categorical/state/effect observations. Future 1%,2%,5%,10% require a useful metric, explicit domain and exact reference.
approximant
Forward relation
Confined DirFs and explicit unrestricted RealFs adapters.
DirFs.new canonicalizes existing directory. real_path normalizes virtual components, joins root, checks canonical deepest existing ancestor; final symlinks require canonical target inside root. with runs OS operation after check then logs result; RealFs.with directly applies OS operation.
Domain: bounded inputs with available allocation and nonoverflowing counters unless checked explicitly. The relation is partial and source-derived.
composition
Composition
Confined DirFs and explicit unrestricted RealFs adapters. Shared state and order: DirFs.new canonicalizes existing directory. real_path normalizes virtual components, joins root, checks canonical deepest existing ancestor; final symlinks require canonical target inside root. with runs OS operation after check then logs result; RealFs.with directly applies OS operation.
Scoped children project this same source. Their domains and effects remain conditional; source execution connects these clauses rather than independently proving their wiring. Under stable filesystem and safe temp prefix, DirFs regular access remains rooted; TOCTOU invalidates concurrent adversarial confinement. Metadata reports ctime=mtime,nlink1; host logs bytes0. remove_dir_all rejects exact root.
models
Typed source models
Source-bound partial relations; no universal finite-test proof.
behavior_complement
Subject: vfs-host. Domain: Confined DirFs and explicit unrestricted RealFs adapters. Valid allocations, bounded counters, Fault=None unless explicitly named. Observation: one call or the stated finite trace.
Operator: Stable-root confined read/write cannot follow an outside final symlink or dangling outside target. RealFs has no corresponding confinement complement.
Approximation: source-derived partial relation; complement is an inner excluded-behavior claim under these premises, converse retains compatible antecedents. Evidence: tests.md; unobserved concurrency/resource failures remain unknown.
reverse_reconstruction
Subject: vfs-host. Domain: Confined DirFs and explicit unrestricted RealFs adapters. Valid allocations, bounded counters, Fault=None unless explicitly named. Observation: one call or the stated finite trace.
Operator: Canonical target admits symlink/path aliases and unknown prior host contents. Error/zero-byte journal does not recover actual payload. Metadata projection loses native ctime,nlink and directory-entry inode.
Approximation: source-derived partial relation; complement is an inner excluded-behavior claim under these premises, converse retains compatible antecedents. Evidence: tests.md; unobserved concurrency/resource failures remain unknown.
canonical_preflight
Subject: vfs-host. Domain: Confined DirFs and explicit unrestricted RealFs adapters. Valid allocations, bounded counters, Fault=None unless explicitly named. Observation: one call or the stated finite trace.
Operator: Final dangling symlink returns NotCapable; absent ordinary child probes existing ancestors. Missing interior errors can be deferred to OS.
Approximation: source-derived partial relation; complement is an inner excluded-behavior claim under these premises, converse retains compatible antecedents. Evidence: tests.md; unobserved concurrency/resource failures remain unknown.
race_boundary
Subject: vfs-host. Domain: Confined DirFs and explicit unrestricted RealFs adapters. Valid allocations, bounded counters, Fault=None unless explicitly named. Observation: one call or the stated finite trace.
Operator: Check and access are separate syscalls; no openat capability proof. NoConfine mutation bypasses the preflight.
Approximation: source-derived partial relation; complement is an inner excluded-behavior claim under these premises, converse retains compatible antecedents. Evidence: tests.md; unobserved concurrency/resource failures remain unknown.
metadata_projection
Subject: vfs-host. Domain: Confined DirFs and explicit unrestricted RealFs adapters. Valid allocations, bounded counters, Fault=None unless explicitly named. Observation: one call or the stated finite trace.
Operator: mtime nanos cast to u64, ctime copied from mtime, nlink1; read_dir skips nonUTF8 names, sorts byte names, ino0.
Approximation: source-derived partial relation; complement is an inner excluded-behavior claim under these premises, converse retains compatible antecedents. Evidence: tests.md; unobserved concurrency/resource failures remain unknown.
temp_effects
Subject: vfs-host. Domain: Confined DirFs and explicit unrestricted RealFs adapters. Valid allocations, bounded counters, Fault=None unless explicitly named. Observation: one call or the stated finite trace.
Operator: DirFs temp_name creates root/tmp ignoring mkdir error and loops counters until !exists; prefix assumed simple basename, no reservation or sanitation.
Approximation: source-derived partial relation; complement is an inner excluded-behavior claim under these premises, converse retains compatible antecedents. Evidence: tests.md; unobserved concurrency/resource failures remain unknown.
tests
Checks and limitations
Exact named observations: dirfs_confines_to_root, gates_green_and_negative_controls_red.
Fresh receipts: $MOVA_DATA/runs/octopus-wave31-vfs-2026-10-31; run.sh retains four profile/repetition sets with raw logs and numeric statuses. native-commands.json and source-test-map.json disambiguate targets. Compiled mutations and exact restoration are separately retained in mutation-summary.json.
These finite observations are not semantic completeness. Source syntax generated twice and compared byte-for-byte. Host effects are limited to owned TMPDIR fixtures. Existing absolute_paths_never_reach_the_host and open_modes are skipped; snapbench main is skipped. Standalone helpers/reexports are only observed through named callers or representation checks; RealFs effect methods unexecuted.
invariant-and-cost
Invariant and cost
Invariant
Under stable filesystem and safe temp prefix, DirFs regular access remains rooted; TOCTOU invalidates concurrent adversarial confinement. Metadata reports ctime=mtime,nlink1; host logs bytes0. remove_dir_all rejects exact root.
Cost
O(path bytes+ancestor canonicalization syscalls) resolution; OS byte I/O costs; read_dir sort O(k log k), memory O(names+data). No measured speed claim.
No timing or numerical error guarantee is inferred from finite tests.
This page in Markdown → https://md.groupants.elamur.ai/free/en/mova/vfs/src/host.rs.groupant/