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vfs.md

File metadata and controls

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VFS

The vfs package provides a small filesystem abstraction used by WAL, manifest, SST, value-log, and raftstore paths.

1. Core Interfaces

vfs.FS includes:

  • file open/create: OpenHandle, OpenFileHandle
  • path ops: MkdirAll, Remove, RemoveAll, Rename, RenameNoReplace, Stat, ReadDir, Glob
  • helpers: ReadFile, WriteFile, Truncate, Hostname

vfs.File includes:

  • read/write/seek APIs
  • Sync, Truncate, Close, Stat, Name

vfs.Ensure(fs) maps nil to OSFS.

2. Rename Semantics

Rename:

  • normal rename/move semantics.
  • target replacement behavior is platform-dependent (os.Rename behavior).

RenameNoReplace:

  • contract: fail with os.ErrExist when destination already exists.
  • on Linux, uses renameat2(..., RENAME_NOREPLACE).
  • on macOS, uses renamex_np(..., RENAME_EXCL).
  • when atomic no-replace rename is unsupported by platform/filesystem, returns vfs.ErrRenameNoReplaceUnsupported (no non-atomic fallback).

3. Directory Sync Helper

vfs.SyncDir(fs, dir) fsyncs directory metadata to persist entry updates (create/rename/remove).

This is used in strict durability paths (for example SST install before manifest publication) to guarantee directory entry persistence.

4. Fault Injection (FaultFS)

FaultFS wraps an underlying FS and can inject failures by operation/path.

  • Rule helpers: FailOnceRule, FailOnNthRule, FailAfterNthRule, FailOnceRenameRule
  • File-handle faults: write/sync/close/truncate
  • Rename fault matching supports src/dst targeting

Used to test manifest/WAL/recovery failure paths deterministically.

5. Current Implementation Set

  • OSFS: production implementation (Go os package).
  • FaultFS: failure-injection wrapper over any FS.

No in-memory FS is included yet.

6. Design Notes

  • Keep storage code decoupled from direct os.* calls.
  • Make crash/failure tests reproducible.
  • Keep API minimal and only add operations required by real storage call sites.

References: