littlefs API + bindings for Nim

This is still experimental since I have not tested it or used it at all.

Observe copyright and distribution license of littlefs from their GitHub repository:

Copyright (c) 2022, The littlefs authors. Copyright (c) 2017, Arm Limited. All rights reserved.

Boot count example

This example is translated from the littlefs GitHub README

import littlefs/all
import littlefs/configs/file_config

import std/os

const fsPath = "testfs.bin"

var f = open(fsPath, if fileExists(fsPath): fmReadWriteExisting else: fmReadWrite)
var lfs = LittleFs(cfg: makeFileLfsConfig(f, block_count=1024))
lfs.boot()
var file = lfs.open("boot_count", fmReadWrite)
var boot_count = read[int](file)
echo "boot count: ", boot_count
inc boot_count
file.rewind()
file.write(boot_count)

Project directory

examples
src
  ---> littlefs
    ---> api                High level API
    ---> bindings           Thin wrapping
      ---> lfs_nimutil.nim  Nim implementation of lfs_util.h
    ---> configs            Modules for premade configs
tests                       Nothing yet
buildsys.nims               Build system will go here if needed

Building with buildsys.nims

This library comes with a Nim implementation of lfs_util.h. To use it define lfsUseNimUtils. The build tasks and the api both observe this definition.

The following will clone littlefs and build it. This task will build two versions of the littlefs C library, one of which is compiled expecting the Nim implementation of lfs_util.h. Library files will be dropped at build/liblfs.a and build/liblfsNim.a respectively:

nim buildLfsLibs buildsys.nims

To build the littlefs C source with asserts, errors and warnings disabled:

nim -d:danger buildLfsLibs buildsys.nims

To build the fuse driver run:

nim buildFuse buildsys.nims

or

nim -d:lfsUseNimUtils -d:release buildFuse buildsys.nims

---

You can import "config.nims", or if in nimble path, littlefs/api/build_help/config.nims to have the c sources automatically added via cincludes and the correct library given the state of lfsUseNimUtils.

The api file common.nim will import and export bindings/lfs_nimutil.nim when lfsUseNimUtils is defined so that it is easy to compile with this option enabled

FYIs

• The destructors are designed to try and clean up before destroying the LittleFs object, but this is not supported by the littlefs C library as far as I'm aware. I did my best, but I can't guarantee it will work.
• File objects and Dir objects are heap allocated refs. This is because they must maintain a constant memory address for littlefs to function properly. It's easy enough to handle them on the stack if you want to, but you might have to use the thin wrappings in bindings to use the API functions as they expect ref objects
• Although it may be annoying the error handling mechanism is a global var LfsErrNo that you have to manually check. Maybe this will change in future
• This project does not conform to Nim's style guide and I do not intend to. If there are self-contained inconsistencies, then I will fix them
• Atlas will be the target env management program, nimble related things will be maintained at bare minimum
• The default configurations are not exactly sane, just change them to fit your needs. They should probably be explicitly defined anyways

Future plans

• Configs for nesper (ESP32)
• Maybe more API features as I need them (PRs welcome)
  • Maybe implement user attributes
• Maybe implement exceptions with a -d:lfsExceptions