About

The main goal of the lwext4 project is to provide ext2/3/4 filesystem for microcontrollers. It may be an interesting alternative for traditional MCU filesystem libraries (mostly based on FAT32).

Lwext4 may be used with SD/MMC card, USB flash drive or other block based memory device. However it is not good for flash memory–based storage devices.

Code is also available on github: https://github.com/gkostka/lwext4

Feel free to contact me: kostka.grzegorz@gmail.com

Credits

The most of the source code of lwext4 was taken from HelenOS:

• http://helenos.org/ Some features are based on FreeBSD and Linux implementations.

KaHo Ng (https://github.com/ngkaho1234):

• advanced extents implementation
• xattr support
• metadata checksum support
• journal recovery
• many bugfixes & improvements

fuse-lwext4 project:

• https://github.com/ngkaho1234/fuse-lwext4

Features

• filetypes: regular, directories, softlinks
• support for hardlinks
• multiple blocksize supported: 1KB, 2KB, 4KB ... 64KB
• little/big endian architectures supported
• multiple configurations (ext2/ext3/ext4)
• only C standard library dependency
• various CPU architectures supported (x86/64, cortex-mX, msp430 ...)
• small memory footprint

Memory footprint (for cortex-m4)

• .text: 20KB - 40KB
• .data: 8KB (minimum 8 x 1KB block cache)
• .stack: 2KB

Supported ext2/3/4 features

Features incompatible:

• compression: no
• filetype: yes
• recover: no
• journal_dev: no
• meta_bg: yes
• extents: yes
• 64bit: yes
• mmp: no
• flex_bg: yes
• ea_inode: no
• dirdata: no
• bg_meta_csum: no
• largedir: no
• inline_data: no

Features compatible:

• dir_prealloc: no
• imagic_inodes: no
• has_journal: yes (in progress)
• ext_attr: yes
• resize_inode: no
• dir_index: yes

Features read-only:

• sparse_super: yes
• large_file: yes
• btree_dir: yes
• huge_file: yes
• gdt_csum: yes
• dir_nlink: yes
• extra_isize: yes
• quota: no
• bigalloc: no
• metadata_csum: yes

Project tree

• blockdev - block devices set, supported blockdev
• fs_test - test suite, mkfs and demo application
• lwext4 - internals of the lwext4 library
• toolchain - specific toolchain cmake files
• CMakeLists.txt - CMake config file
• ext_images.7z - compressed ext2/3/4 100MB images
• fs_test.mk - automatic tests definitions
• Makefile - helper makefile to generate cmake and run test suite
• readme.mediawiki - readme file

Compile

Dependencies

• Windows

Download MSYS-2: https://sourceforge.net/projects/msys2/

Install required packages is MSYS2 Shell package manager:

 pacman -S make gcc cmake p7zip

• Linux

Package installation (Debian):

 apt-get install make gcc cmake p7zip

Compile & install tools

 make generic
 cd build_generic
 make
 sudo make install

lwext4-generic demo application

Simple lwext4 library test application:

• load ext2/3/4 images
• load linux block device with ext2/3/4 part
• load windows volume with ext2/3/4 filesystem
• directory speed test
• file write/read speed test

How to use for images/blockdevices:

 lwext4-generic -i ext_images/ext2 
 lwext4-generic -i ext_images/ext3 
 lwext4-generic -i ext_images/ext4 

Show full option set:

 lwext4-generic --help

Run automatic tests

Execute tests for 100MB unpacked images:

 make test

Execute tests for autogenerated 1GB images (only on Linux targets) + fsck:

 make test_all

Using lwext4-mkfs tool

It is possible to create ext2/3/4 partition by internal library tool.

Generate empty file (1GB):

 dd if=/dev/zero of=ext_image bs=1M count=1024

Create ext2 partition:

 lwext4-mkfs -i ext_image -e 2

Create ext3 partition:

 lwext4-mkfs -i ext_image -e 3

Create ext4 partition:

 lwext4-mkfs -i ext_image -e 4

Show full option set:

 lwext4-mkfs --help

Cross compile standalone library

Toolchains needed:

• arm-none-eabi-gcc for cortex-mX
• avr-gcc for avr
• bfin-elf-gcc for bfin
• msp430-gcc for msp430

Build bf518 library:

 make bf518
 cd build_bf518
 make lwext4

Build avrxmega7 library:

 make avrxmega7
 cd build_avrxmega7
 make lwext4

Build cortex-m0 library:

 make cortex-m0
 cd build_cortex-m0
 make lwext4

Build cortex-m3 library:

 make cortex-m3
 cd build_cortex-m3
 make lwext4

Build cortex-m4 library:

 make cortex-m4
 cd build_cortex-m4
 make lwext4