---
title: "vfs-host — Mova code model"
description: "Mova code model of vfs/src/host.rs: components with their labels, obernants and the model text."
url: "https://groupants.elamur.ai/free/en/mova/vfs/src/host.rs.groupant/"
---
Elamur: [Mova](https://md.mova.elamur.ai/free/en/) · [Dictionary](https://md.dictionary.elamur.ai/free/en/) · [Research](https://md.research.elamur.ai/free/en/) · **Groupants**

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# vfs-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

- **kind:** groupant
- **status:** partial source bound model
- **source:** [`vfs/src/host.rs`](https://github.com/ElamurAI/mova-free/blob/main/vfs/src/host.rs)
- **source SHA-256:** `d7a0bb0efff6f8f4…`
- **repository folder:** [`vfs/src/host.rs.groupant`](https://github.com/ElamurAI/mova-free/tree/main/vfs/src/host.rs.groupant)
- **repository commit:** `855da7bd4a7b`

> **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](#approximant) |
| **ast** | partial | `syntax.json` |
| **composition** | partial | [composition](#composition) |
| **cost** | partial | [Cost](#cost) |
| **descriptant** | present | [descriptant](#descriptant) |
| **invariant** | partial | [Invariant](#invariant) |
| **tests** | executed bounded checks | [tests](#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](#behavior-complement) |
| `reverse_reconstruction` | reverse_reconstruction | partial source derived model | [reverse_reconstruction](#reverse-reconstruction) |
| `canonical_preflight` | canonical_preflight | partial source derived model | [canonical_preflight](#canonical-preflight) |
| `race_boundary` | race_boundary | partial source derived model | [race_boundary](#race-boundary) |
| `metadata_projection` | metadata_projection | partial source derived model | [metadata_projection](#metadata-projection) |
| `temp_effects` | temp_effects | partial source derived model | [temp_effects](#temp-effects) |

## Parts

- [vfs-host-confinement](https://md.groupants.elamur.ai/free/en/mova/vfs/src/host.rs.groupant/confinement.groupant/)

## 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.