lwext4

About lwext4
============

The main goal of the lwext4 project is to provide ext2/3/4 filesystem
library for microcontrolers with SD/MMC card support. Ext2/3/4, in my
opinion is one of the best filesystem for SD/MMC.

kostka.grzegorz@gmail.com

Minimum memory requirements
===========================

.text ~ 15KB
.data + .bss ~ 8KB
.stack ~ 1KB-2KB (not tested yet)

ext2/3/4 vs FAT32
=================
ext2/3/4 > FAT32
- fseek operation on big file in FAT32 is IO heavy
- ext2/3/4 HTREE directories operations are faster than FAT32
- ext4 extents makes truncate/remove opertion really fast
- more at https://ext4.wiki.kernel.org/index.php/Ext4_Disk_Layout

ext2/3/4 < FAT32
- FAT32 has smaller footprint

Credits lwext4
==============

A lot of the implementation of lwext4 was taken from HelenOS:
- http://www.helenos.org/

Some of ideas and features are based on FreeBSD and Linux implementations.

lwext4 supported/unsupported ext2/3/4 fs features
=================================================
FEATURE_INCOMPAT (unable to mount with unsupported feature):
- COMPRESSION: no
- FILETYPE: yes
- RECOVER: no
- JOURNAL_DEV: no
- META_BG: no
- EXTENTS: yes
- 64BIT: yes
- MMP: no
- FLEX_BG: no
- EA_INODE: no
- DIRDATA: no

FEATURE_INCOMPAT (able to mount with unsupported feature):
- DIR_PREALLOC: no
- IMAGIC_INODES: no
- HAS_JOURNAL: no
- EXT_ATTR: no
- RESIZE_INODE: no
- DIR_INDEX: yes

FEATURE_RO (able to mount in read only with unsupported feature):
- SPARSE_SUPER: yes
- LARGE_FILE: yes
- BTREE_DIR: no
- HUGE_FILE: yes
- GDT_CSUM: yes
- DIR_NLINK: yes
- EXTRA_ISIZE: yes

Supported filetypes:
- FIFO: no
- CHARDEV: no
- DIRECTORY: yes
- BLOCKDEV: no
- FILE: yes
- SOFTLINK: no
- SOCKET: no

Other:
- block_size: 1KB, 2KB, 4KB ... 64KB
- little/big endian architecture support


lwext4 project tree
===================

+blockdev - block devices set, supported blockdevs
- filedev - file based block device
- io_raw - wiodows IO block device

+demos - demo directory sources
- generic - generic demo app, used for development and and debbuging purpose

+lwext4 - internals of the lwext4 library

+toolchain - specific toolchain cmake files

+ext4.h - lwext4 client library header
CMakeLists.txt - CMake config file
ext_images.7z - ext2/3/4 100MB images
Makefile - helper makefile to call cmake
readme.txt - yes, you are here ;)

lwext4 compile Windows
======================

Tools needed:
- CMake: http://www.cmake.org/cmake/resources/software.html
- MinGw: http://www.mingw.org/
- GnuWin: http://gnuwin32.sourceforge.net/

Build:
>>make

Clean:
>>clean

Successful build generates out of source build directory:
+build_generic

lwext4 compile Linux
====================
Tools needed:
- CMake: http://www.cmake.org/cmake/resources/software.html

Build:
>>make

Clean:
>>clean

Successful build generates out of source build directory:
+build_generic

lwext4 generic demo app
=======================

Features:
- 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:
Windows/Linux fileimages:
> cd build_generic
> fileimage_demo --in ext2

Windows volumes:
> cd build_generic
> fileimage_demo --in I: --wpart

Linux block devices:
> cd build_generic
> fileimage_demo --in /dev/your_block_device

Usage:
--i - input file (default = ext2)
--rws - single R/W size (default = 1024 * 1024)
--rwc - R/W count (default = 10)
--cache - 0 static, 1 dynamic (default = 1)
--dirs - directory test count (default = 0)
--clean - clean up after test
--bstat - block device stats
--sbstat - superblock stats
--wpart - windows partition mode


lwext4 compile Cross
====================

Toolchain for ARM Cortex-m3/4: https://launchpad.net/gcc-arm-embedded
Toolchain for Blackfin: http://blackfin.uclinux.org/doku.php

Build bf158 library:
> make bf518

Build cortex-m3 library:
> make cortex-m3

Build cortex-m4 library:
> make cortex-m4

lwext4 ports
============

Blackfin BF518 EZKIT SD Card Demo: TBD
STM32F4-Discovery SD Card Demo: TBD


lwext4 footprint
================

TBD