IRIX FAT32 Filesystem Driver

A loadable kernel module providing FAT32 filesystem support for SGI IRIX 6.5.

Overview

This driver implements a fully functional FAT32 filesystem handler for IRIX 6.5 systems. It supports reading and writing FAT32-formatted media, enabling IRIX systems to access modern storage devices formatted with FAT32.

Features

• Full read/write support for FAT32 filesystems
• Loadable kernel module (no kernel rebuild required for testing)
• Permanent installation option for production use
• Support for multiple IRIX platforms: IP30 (Octane), IP32 (O2), IP35 (Fuel/Tezro/Origin 350)
• Big-endian MIPS CPU compatible
• Cluster-based file/directory access optimized for IRIX block layer cache

Technical Details

• Compiler: MIPSPro C 7.4.4
• Language Standard: C99
• Architecture: Big-endian MIPS
• Inode Strategy: Uses FAT32 cluster directory number/starting entry index/size for ino_t (root = 1)
• Endianness Handling: RLE16/WLE16/RLE32/WLE32 macros for little-endian FAT data

Prerequisites

• IRIX 6.5.x system
• MIPSPro C compiler 7.4.4
• Root access for installation and loading
• Development headers installed (/var/sysgen/ directory)

Building

Configure Build Options

Edit the Makefile and set the CPUBOARD variable to match your system:

CPUBOARD=IP30    # For Octane
CPUBOARD=IP32    # For O2
CPUBOARD=IP35    # For Fuel, Tezro, Origin 350

For loadable module mode (default):

BUILTIN=0

For permanent kernel built-in mode:

BUILTIN=1

Compile the Module

smake

This builds:

• fat32.o - The loadable kernel module
• mount_fat32 - User-space mount utility

Clean Build Artifacts

smake clean

Installation

Option 1: Loadable Module (Recommended for Testing)

Load the module into the running kernel without rebooting:

# Build the module
smake

# Load into kernel
smake load

# Verify it's loaded
smake list

To unload the module:

smake unload

To reload (useful during development):

smake reload

Option 2: Permanent Installation

Install the module as a permanent part of the kernel.

First, set BUILTIN=1 in the Makefile:

BUILTIN=1

Then build and install:

# Build the module for built-in installation
smake

# Install files to system directories
smake install

This copies:

• fat32 → /var/sysgen/master.d/ (master configuration)
• fat32.o → /var/sysgen/boot/ (kernel module)
• fat32.sm → /var/sysgen/system/ (system configuration)
• mount_fat32 → /sbin/ (mount utility)

After installation:

# Rebuild the kernel
autoconfig

# Reboot to load the new kernel
shutdown -y -g0 -i6

Or use the provided shortcut:

smake reboot

Usage

Mounting a FAT32 Filesystem

The driver can mount either:

• A specific FAT32 partition (e.g., /dev/dsk/dks1d4s7)
• A whole volume, which will mount the first partition (e.g., /dev/dsk/dks1d4vol)

Using the mount utility:

# Create mount point
mkdir -p /mnt/fat32

# Mount a specific FAT32 partition
/sbin/mount_fat32 /dev/dsk/dks1d4s7 /mnt/fat32

# Or mount the first partition on a whole volume
/sbin/mount_fat32 /dev/dsk/dks1d4vol /mnt/fat32

# Mount with specific partition number (0-3)
/sbin/mount_fat32 -o part=1 /dev/dsk/dks1d4vol /mnt/fat32

# Mount with custom ownership (all files owned by uid 1000, gid 100)
/sbin/mount_fat32 -o uid=1000,gid=100 /dev/dsk/dks1d4vol /mnt/fat32

# Combine options
/sbin/mount_fat32 -o part=2,uid=1000,gid=100,ro /dev/dsk/dks1d4vol /mnt/fat32

Mount Options

The following options can be passed via -o:

Option	Description
part=N	Mount partition N (0-3) from MBR. If not specified, auto-detects first FAT32 partition.
uid=N	Set owner uid for all files (default: 0/root)
gid=N	Set owner gid for all files (default: 0/root)
ro	Mount read-only
rw	Mount read-write (default)

Using the Makefile convenience target (mounts to /fat):

smake mount

Working with DOS-Partitioned Drives

IRIX does not natively understand DOS partition tables. To access specific FAT32 partitions on a DOS-partitioned drive, you can use XLV (IRIX Logical Volume Manager) to define volumes that match the FAT partition boundaries:

# Use xlv_make to create a logical volume matching the FAT partition
# Example: Create a volume for a partition starting at block 2048, length 20971520 blocks
xlv_make -d partition_name /dev/dsk/dks1d4vol 2048 20971520

This allows you to create device nodes (e.g., /dev/dsk/partition_name) that align with individual FAT32 partitions on drives with DOS partition tables.

Unmounting

umount /mnt/fat32

Development

Testing on Live System

You can test the driver on a live IRIX 6.5.22 system:

Host: octopus
User: root
Password: p00pp00p
Source Tree: /root/fat32

Connect via telnet:

telnet octopus

Source Structure

• fat32fs.c - Main filesystem driver initialization
• fat32_vfs.c - VFS operations (mount, unmount, statvfs)
• fat32_vnode.c - Vnode operations (getattr, setattr, access, etc.)
• fat32_dir.c - Directory operations (lookup, readdir, create, remove)
• fat32_file.c - File I/O operations (read, write)
• fat32_util.c - Utility functions (cluster chains, FAT access)
• fat32_cls.c - Cluster allocation and management
• fat32fs.h - Main header with IRIX kernel interface
• fat32.h - FAT32 data structures and constants
• mount_fat32.c - User-space mount utility

Important Implementation Notes

• Files and directories are accessed in cluster chunks
• Boot sectors and FAT area are accessed in single cluster chunks
• This design is critical because IRIX block layer cache doesn't handle overlapping chunks
• Little-endian data from FAT is handled using RLE16/WLE16/RLE32/WLE32 macros

Makefile Targets

Target	Description
all	Build the loadable module and mount utility (default)
load	Load the driver into the running kernel
unload	Unload the driver from the kernel
reload	Unload then reload the driver
list	List currently loaded modules
clean	Remove build artifacts
install	Install for permanent kernel integration
mount	Quick mount test volume to /fat
reboot	Reboot the system
help	Display Makefile help

License

This is an IRIX kernel module developed for SGI IRIX 6.5 systems. It is licensed under BSD-3 clause license in file LICENSE.