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Linux Filesystem and Utilities

This section provides some information regarding tools and utilities for building filesystems targetting Embedded Linux platforms. These can vary depending on the level of functionality available on the development platform used as well as the type of applications for which this platform will be used.

Multiple options available for creating base filesystems:

• cramfs is a read-only filesystem designed for simplicity and space-efficiency. The base utilities can be accessed on sourceforge project's page.
• romfs is a read-only filesystem originally for Linux. It is a space-efficient, small block-based filesystem.
• JFFS2 is a log-structured file system designed for use on flash devices in embedded systems.
• SquashFS is a compressed read-only filesystem for Linux. It is intended for general read-only filesystem use, for archival use and in constrained block device/memory systems (e.g. embedded systems) where low overhead is needed.
• NFS Network FileSystem.

AEL File Systems

A basic glibc file system for linux is available from www.arm.com::Linux Operating System Download.
More details, including errata
Using buildroot with the Code Sourcery tools tp produce a uClibc uclinux file system

MTD Driver

The Memory Technology Device (MTD) subsystem for Linux provides a generic interface to memory devices such as Flash and RAM. It provides read, write and erase access to the board memory devices. The mtdblock devices can be mounted by jffs, jffs2 and cramfs filesystems. The MTD driver provides extensive support for NOR Flash devices with support for common flash interfaces (CFI). The width of the Flash bus and number of chips required to implement the bus width can be manually configured or automatically detected. The MTD driver layer also supports multiple Flash partitions on one set of Flash devices. Additional documentation can be found in the drivers/mtd directory of the Linux kernel sources and the kernel documentation pages.

NFS Swap File

I've successfully used/adapted the instructions at http://www.nslu2-linux.org/wiki/HowTo/MountNFSSwapPartition on VersatilePB926 says
mailto:peter.pearse@armNO-SPAM.com.

• Kernel 2.6.19 patched to arm2.
• Kernel configure for swap file && loop back device.
• Haven't tested the boot up script yet.

ARM/Thumb-2 Size Comparison

Thumb-2 file system This is a basic file system (no networking, no X11 etc.).
It boots on the ARM RVDS v4.0 Cortex-A8 model, with a linux 2.6.21 ARM compiled kernel providing Thumb-2 support.
The attached file, arm_t2.xls, compares the Thumb-2 files with the ARM equivalents.
A maximum reduction in size of 28% is observed (usr/lib/libformw.so.5.5 ). This gives a reduction of 16% across all the files (executables & libraries).