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📁 Little FS ​

The little_fs crate is the concrete LittleFS backend that implements Xila's file-system contracts.

Role ​

  • Implements file_system::FileSystemOperations and related traits on top of littlefs2-sys.
  • Provides mount/format bootstrap paths used before VFS initialization.

Boundaries ​

  • In scope: backend adaptation, attribute translation, file/directory context operations.
  • Out of scope: global mount namespace and path policy (owned by VFS).

Internal structure ​

  • file_system.rs: FileSystem type, mount/format lifecycle, trait implementations.
  • callbacks.rs + configuration.rs: glue from DirectBlockDevice to LittleFS C callbacks/config.
  • file.rs / directory.rs: context-specific file and directory operations.
  • attributes.rs / flags.rs: mapping between Xila and LittleFS representations.
  • error.rs: LittleFS result-to-file_system::Error conversion.

Runtime interaction ​

  1. Backend is created via FileSystem::new(...), new_format(...), or get_or_format(...).
  2. It mounts using littlefs::lfs_mount and seeds root internal attributes if missing.
  3. VFS calls trait methods; crate routes calls through a mounted mutex wrapper.
  4. On drop, it unmounts and releases leaked configuration context.

Dependency model ​

Failure semantics ​

  • Mount/format/operation failures are translated to file_system::Error.
  • get_or_format retries by formatting when initial mount fails.
  • Context type mismatch in operation dispatch returns InvalidParameter.

Extension points ​

  • Additional mount policies can wrap existing constructors.
  • New attribute/flag translations can be added without changing trait-level contracts.

Contract vs implementation ​

  • Contract: fully conforms to file_system trait interfaces expected by VFS.
  • Current implementation: based on LittleFS C runtime (lfs_*) with MutexMountWrapper<CriticalSectionRawMutex, lfs_t>.

Limitations and trade-offs ​

  • Behavior inherits LittleFS semantics and target storage constraints.
  • Relies on callback/config correctness; misconfigured block geometry can fail at runtime.

References ​