This is the Mbed OS API for littlefs, a little fail-safe filesystem designed for embedded systems.
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--|o |---| littlefs |
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Bounded RAM/ROM - The littlefs is designed to work with a limited amount of memory. Recursion is avoided, and dynamic memory is limited to configurable buffers that can be provided statically.
Power-loss resilient - The littlefs is designed for systems that may have random power failures. The littlefs has strong copy-on-write guarantees, and storage on disk is always kept in a valid state.
Wear leveling - Because the most common form of embedded storage is erodible flash memories, littlefs provides a form of dynamic wear leveling for systems that cannot fit a full flash translation layer.
If you are already using a filesystem in Mbed, adopting the littlefs should just require a name change to use the LittleFileSystem2 class.
Here is a simple example that updates a file named "boot_count" every time the application runs:
#include "LittleFileSystem2.h"
#include "SPIFBlockDevice.h"
// Physical block device, can be any device that supports the BlockDevice API
SPIFBlockDevice bd(PTE2, PTE4, PTE1, PTE5);
// Storage for the littlefs
LittleFileSystem2 fs("fs");
// Entry point
int main() {
// Mount the filesystem
int err = fs.mount(&bd);
if (err) {
// Reformat if we can't mount the filesystem,
// this should only happen on the first boot
LittleFileSystem2::format(&bd);
fs.mount(&bd);
}
// Read the boot count
uint32_t boot_count = 0;
FILE *f = fopen("/fs/boot_count", "r+");
if (!f) {
// Create the file if it doesn't exist
f = fopen("/fs/boot_count", "w+");
}
fread(&boot_count, sizeof(boot_count), 1, f);
// Update the boot count
boot_count += 1;
rewind(f);
fwrite(&boot_count, sizeof(boot_count), 1, f);
// Remember that storage may not be updated until the file
// is closed successfully
fclose(f);
// Release any resources we were using
fs.unmount();
// Print the boot count
printf("boot_count: %ld\n", boot_count);
}DESIGN.md - DESIGN.md contains a fully detailed dive into how littlefs actually works. We encourage you to read it because the solutions and tradeoffs at work here are quite interesting.
SPEC.md - SPEC.md contains the on-disk specification of littlefs with all the nitty-gritty details. This can be useful for developing tooling.
littlefs - Where the core of littlefs currently lives.
littlefs-fuse - A FUSE wrapper for littlefs. The project allows you to mount littlefs directly in a Linux machine. This can be useful for debugging littlefs if you have an SD card handy.
littlefs-js - A JavaScript wrapper for littlefs. I'm not sure why you would want this, but it is handy for demos. You can see it in action here.