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File Systems
NtinosTheGamer2324 edited this page Dec 11, 2025
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ModuOS supports multiple file systems through a unified Virtual File System (VFS) layer with drive letter mounting (A-Z).
┌────────────────────────────────────────────────────┐
│ Application Layer │
│ fs_read_file() / fs_list_directory() │
└────────────────┬───────────────────────────────────┘
│
┌────────────────▼───────────────────────────────────┐
│ Virtual File System (VFS) │
│ - Mount table (A-Z slots) │
│ - Unified file operations │
│ - Path resolution │
└────┬──────────────────────┬────────────────────────┘
│ │
┌────▼──────┐ ┌──────▼─────┐
│ FAT32 │ │ ISO9660 │
│ Driver │ │ Driver │
└────┬──────┘ └──────┬─────┘
│ │
└──────────┬───────────┘
│
┌───────────────▼────────────────────────────────────┐
│ Storage Layer │
│ ATA/ATAPI | AHCI/SATA | vDrive │
└────────────────────────────────────────────────────┘
File: src/fs/fs.c
ModuOS uses drive letters (A-Z) similar to DOS/Windows:
typedef struct {
fs_type_t type; // Filesystem type
int handle; // FS-specific handle
int valid; // Is this mount valid?
} fs_mount_t;
static fs_mount_t mount_table[26]; // A-Ztypedef enum {
FS_TYPE_UNKNOWN = 0,
FS_TYPE_FAT32 = 1,
FS_TYPE_ISO9660 = 2
} fs_type_t;Location: src/fs/DOS/FAT32/
FAT32 (File Allocation Table, 32-bit) is the MS-DOS/Windows file system used for compatibility.
Features:
- Maximum file size: 4GB
- Maximum partition size: 2TB
- Long filename support (LFN)
- Read/Write support
Boot Sector:
typedef struct {
uint8_t jmp[3];
char oem_name[8];
uint16_t bytes_per_sector;
uint8_t sectors_per_cluster;
uint16_t reserved_sectors;
uint8_t num_fats;
uint16_t root_entries; // 0 for FAT32
uint16_t total_sectors_16; // 0 for FAT32
uint8_t media_type;
uint16_t sectors_per_fat_16; // 0 for FAT32
// ... FAT32 specific fields
uint32_t sectors_per_fat_32;
uint32_t root_cluster;
// ...
} __attribute__((packed)) fat32_boot_sector_t;typedef struct {
char name[11]; // 8.3 format
uint8_t attributes;
uint8_t reserved;
uint8_t creation_time_ms;
uint16_t creation_time;
uint16_t creation_date;
uint16_t access_date;
uint16_t cluster_high; // High 16 bits
uint16_t modified_time;
uint16_t modified_date;
uint16_t cluster_low; // Low 16 bits
uint32_t file_size;
} __attribute__((packed)) fat32_dir_entry_t;int fat32_read_file(int handle, const char *path, void *buffer,
size_t buffer_size, size_t *bytes_read);
int fat32_list_directory(int handle, const char *path);
int fat32_stat(int handle, const char *path, fs_file_info_t *info);Location: src/fs/ISOFS/
ISO9660 is the standard file system for CD-ROMs and DVD-ROMs.
Features:
- Read-only
- Rock Ridge extensions support (Unix permissions)
- Joliet extensions (Unicode filenames)
- Maximum file size: 4GB
typedef struct {
uint8_t type; // 1 = Primary Volume
char identifier[5]; // "CD001"
uint8_t version;
// ... volume info
uint32_t volume_space_size; // Total sectors
uint32_t root_directory_extent;
uint32_t root_directory_size;
// ...
} __attribute__((packed)) iso9660_pvd_t;typedef struct {
uint8_t length;
uint8_t extended_length;
uint32_t extent_lba; // Data location
uint32_t extent_lba_msb;
uint32_t data_length;
uint32_t data_length_msb;
uint8_t recording_date[7];
uint8_t file_flags;
uint8_t file_unit_size;
uint8_t interleave_gap;
uint16_t volume_sequence;
uint16_t volume_sequence_msb;
uint8_t name_length;
char name[0]; // Variable length
} __attribute__((packed)) iso9660_dir_record_t;File: include/moduos/fs/fs.h
// Initialize VFS
void fs_init(void);
// Mount a drive to slot (0-25 = A-Z)
int fs_mount_drive(int drive_index, uint32_t partition_lba, fs_type_t type);
// Unmount slot
int fs_unmount_slot(int slot);
// Get mount handle
fs_mount_t* fs_get_mount(int slot);
// List all mounts
void fs_list_mounts(void);Example:
// Mount drive 0 to A:
fs_mount_drive(0, 0, FS_TYPE_FAT32);
// Mount CD-ROM to D:
fs_mount_drive(1, 0, FS_TYPE_ISO9660);// Read entire file
int fs_read_file(fs_mount_t* mount, const char* path,
void* buffer, size_t buffer_size, size_t* bytes_read);
// Get file info
int fs_stat(fs_mount_t* mount, const char* path, fs_file_info_t* info);
// Check if file exists
int fs_file_exists(fs_mount_t* mount, const char* path);// List directory
int fs_list_directory(fs_mount_t* mount, const char* path);
// Check if directory exists
int fs_directory_exists(fs_mount_t* mount, const char* path);File: src/fs/fd.c
Each process has up to 16 open files:
typedef struct {
int used; // 1 if in use
fs_mount_t *mount; // Mounted filesystem
char path[260]; // File path
uint32_t position; // Current read/write position
uint32_t size; // File size
int flags; // Open flags (read/write)
} file_descriptor_t;// Open file
int fd_open(const char *path, int flags);
// Close file
int fd_close(int fd);
// Read from file
int fd_read(int fd, void *buffer, size_t count);
// Write to file (if supported)
int fd_write(int fd, const void *buffer, size_t count);
// Seek position
int fd_seek(int fd, uint32_t offset, int whence);Absolute path: Z:/ModuOS/System64/mdsys.sqr
- Drive letter:
Z: - Path separator:
/or\ - Case insensitive
Relative path: Not fully supported yet
// Parse "Z:/dir/file.txt"
char drive_letter = path[0]; // 'Z'
int slot = drive_letter - 'A'; // 25
fs_mount_t *mount = fs_get_mount(slot);
const char *file_path = &path[2]; // "/dir/file.txt"- Storage Drivers - Hardware access
- Syscall Reference - File I/O syscalls
- Shell Commands - File operations