---
title: "vfs-error — Mova code model"
description: "Mova code model of vfs/src/error.rs: components with their labels, obernants and the model text."
url: "https://groupants.elamur.ai/free/en/mova/vfs/src/error.rs.groupant/"
---
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This page as HTML: <https://groupants.elamur.ai/free/en/mova/vfs/src/error.rs.groupant/>

# vfs-error

The groupant beside vfs/src/error.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/error.rs`](https://github.com/ElamurAI/mova-free/blob/main/vfs/src/error.rs)
- **source SHA-256:** `014e34da6df42352…`
- **repository folder:** [`vfs/src/error.rs.groupant`](https://github.com/ElamurAI/mova-free/tree/main/vfs/src/error.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) |
| `errno_quotient` | errno_quotient | partial source derived model | [errno_quotient](#errno-quotient) |
| `wasi_bijection` | wasi_bijection | partial source derived model | [wasi_bijection](#wasi-bijection) |
| `detail_precedence` | detail_precedence | partial source derived model | [detail_precedence](#detail-precedence) |
| `limit_partition` | limit_partition | partial source derived model | [limit_partition](#limit-partition) |

## Model text


### descriptant

#### vfs-error

Errno numberings, error details and OS transport.

##### 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(1) fixed23 variants/scans; O(detail bytes) owned string and display.

##### 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

Errno numberings, error details and OS transport.

linux(Perm)=linux(NotCapable)=1; wasi distinguishes 63 and76. from_linux scans ALL excluding NotCapable; from_wasi scans all23. Display(detail)=detail, otherwise text plus Linux code. Unknown OS errno becomes Io with original display.

Domain: bounded inputs with available allocation and nonoverflowing counters unless checked explicitly. The relation is partial and source-derived.

### composition

#### Composition

Errno numberings, error details and OS transport. Shared state and order: linux(Perm)=linux(NotCapable)=1; wasi distinguishes 63 and76. from_linux scans ALL excluding NotCapable; from_wasi scans all23. Display(detail)=detail, otherwise text plus Linux code. Unknown OS errno becomes Io with original display.

Scoped children project this same source. Their domains and effects remain conditional; source execution connects these clauses rather than independently proving their wiring. Within ALL, WASI roundtrip preserves tags; Linux roundtrip preserves all except NotCapable becomes Perm. Detail overrides tag text without changing errno.

### models

## Typed source models

Source-bound partial relations; no universal finite-test proof.

### behavior_complement

Subject: vfs-error. Domain: Errno numberings, error details and OS transport. Valid allocations, bounded counters, Fault=None unless explicitly named. Observation: one call or the stated finite trace.

Operator: Under declared enum universe, WASI decoding does not map76 to Perm; known Linux2 does not become Io. Detail-bearing display cannot append automatic OS suffix.

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-error. Domain: Errno numberings, error details and OS transport. Valid allocations, bounded counters, Fault=None unless explicitly named. Observation: one call or the stated finite trace.

Operator: Linux code1 has compatible tags {Perm,NotCapable}; from_linux chooses Perm. Display with arbitrary detail cannot reconstruct errno or OS cause; recognized WASI codes recover exactly one tag.

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.

### errno_quotient

Subject: vfs-error. Domain: Errno numberings, error details and OS transport. Valid allocations, bounded counters, Fault=None unless explicitly named. Observation: one call or the stated finite trace.

Operator: Linux transport forms one non-singleton fiber {Perm,NotCapable}; this is intentional information loss, not inverse equality.

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.

### wasi_bijection

Subject: vfs-error. Domain: Errno numberings, error details and OS transport. Valid allocations, bounded counters, Fault=None unless explicitly named. Observation: one call or the stated finite trace.

Operator: On 23 emitted u16 codes, from_wasi(wasi(e))=Some(e); unknown code has None.

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.

### detail_precedence

Subject: vfs-error. Domain: Errno numberings, error details and OS transport. Valid allocations, bounded counters, Fault=None unless explicitly named. Observation: one call or the stated finite trace.

Operator: FsError{errno,Some(d)} displays d even when empty; default text depends on errno only when None.

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.

### limit_partition

Subject: vfs-error. Domain: Errno numberings, error details and OS transport. Valid allocations, bounded counters, Fault=None unless explicitly named. Observation: one call or the stated finite trace.

Operator: is_limit true exactly for FBig,NoSpc,DQuot; root escape belongs to denied category instead.

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: error::wave31::errno_fibers_and_display.

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

Within ALL, WASI roundtrip preserves tags; Linux roundtrip preserves all except NotCapable becomes Perm. Detail overrides tag text without changing errno.

### Cost

O(1) fixed23 variants/scans; O(detail bytes) owned string and display.

No timing or numerical error guarantee is inferred from finite tests.