[−][src]Crate littlefs2

littlefs is a filesystem for microcontrollers written in C, that claims to be fail-safe:

power-loss resilience, by virtue of copy-on-write guarantees
bounded RAM/ROM, with stack-allocated buffers

Since version 2, it has some nifty features such as:

dynamic wear-leveling, including detection of bad Flash blocks
custom user attributes
inline files, avoiding block waste

For more background, see its design notes and the specification of its format.

What is this?

This library, littlefs2, offers an idiomatic Rust API for littlefs.

It follows the design of std::fs as much as reasonable, and builds on the bindings littlefs2-sys.

Some complications arise due to the lack of const generics in Rust, we work around these with the generic-array library, and long for the day when constants associated to traits will be treated as constants by the compiler.

⯈ The best place to start reading the API docs is here. ⯇

Usage

To use this library, implement littlefs2::driver::Storage. The macro ram_storage! generates examples of this.

Roughly speaking, the Storage trait defines a block device in terms of actual and typenum constants, and an implementation supplies methods to read, erase and write.

The filesystem and each open file need memory for state and caching, this has to be allocated beforehand and passed to constructors.

Design notes

All operations on the filesystem require passing a &mut Storage, which guarantees by Rust's borrow checker that only one thread can manipulate the filesystem. This design choice (as opposed to consuming the Storage, which would be less verbose) was made to enable use of the underlying flash peripheral outside of the filesystem (the Storage can be dropped and reconstructed). For instance, one could setup an additional filesystem, or handle some flash data manually.

As an experiment, we implemented ReadDirWith. It converts a ReadDir (which needs mutable references, and so is "not quite an iterator" over the files of a directory), into a true iterator, by temporarily binding the mutable references.

Currying with lifetime gymnastics!

In the future, we may extend this approach to other operations, thus adding a secondary API layer.

Separately, keeping track of the allocations is a chore, we hope that Pin magic will help fix this.

Example

// example storage backend
ram_storage!(tiny);
let mut ram = Ram::default();
let mut storage = RamStorage::new(&mut ram);

// must format before first mount
Filesystem::format(&mut storage).unwrap();
// must allocate state statically before use
let mut alloc = Filesystem::allocate();
let mut fs = Filesystem::mount(&mut alloc, &mut storage).unwrap();

// must allocate state statically before use
let mut alloc = File::allocate();
// may use common `OpenOptions`
let mut file = OpenOptions::new()
	.read(true)
	.write(true)
	.create(true)
	.open("example.txt", &mut alloc, &mut fs, &mut storage)
	.unwrap();

// may read/write/seek as usual
file.write(&mut fs, &mut storage, b"Why is black smoke coming out?!").unwrap();
file.seek(&mut fs, &mut storage, SeekFrom::End(-24)).unwrap();
let mut buf = [0u8; 11];
assert_eq!(file.read(&mut fs, &mut storage, &mut buf).unwrap(), 11);
assert_eq!(&buf, b"black smoke");

Modules

consts	Re-export of `typenum::consts`. Type aliases for many constants.
driver	The `Storage`, `Read`, `Write` and `Seek` driver.
fs	Filesystem manipulation operations.
io	Traits and types for core I/O functionality.
macros	cf. Macros documentation
path	Path manipulation
prelude	Export of the Read, Write and Seek traits for ease of use.

[−][src]Crate littlefs2

What is this?

Usage

Design notes

Example

Modules

Macros

Structs

Functions