ISO9660

ISO9660 is the read-only CD-ROM filesystem, mounted at /mnt/iso. It is available only when a CD image is attached (QEMU -cdrom). The driver is probed at boot; if no disc is detected, /mnt/iso is not added to the mount table.

All paths under /mnt/iso/ are dispatched to this driver by the VFS. Write operations on ISO9660 paths return InvalidInput immediately — the filesystem is strictly read-only.

Hardware: ATAPI PIO (`fs/iso9660/block.rs`)

Atapi reads 2048-byte ISO9660 blocks from the secondary IDE master (0x170) using PIO mode (no DMA).

I/O Ports

Offset	Register
`0x170`	Data (16-bit)
`0x171`	Features / Error
`0x174`	Byte Count Low
`0x175`	Byte Count High
`0x176`	Drive/Head Select
`0x177`	Command / Status
`0x376`	Alt Status (4× reads = ~400 ns I/O delay)

`read_block(lba, buf)` Sequence

1. port 0x176 ← 0xA0          Select secondary master
   4× read 0x376               ~400 ns I/O delay

2. port 0x171 ← 0x00          PIO mode (no DMA)
   port 0x174 ← 0x00          Transfer size = 2048 = 0x0800
   port 0x175 ← 0x08
   port 0x177 ← 0xA0          ATA PACKET command

3. wait_drq(): spin on status until BSY=0 and (DRQ=1 or ERR=1)

4. Write 12-byte READ(10) SCSI/ATAPI command as 6 × u16 to port 0x170:
     [0x0028]          opcode READ(10), flags=0
     [LBA bits 31:16]  big-endian halves of the 32-bit LBA
     [LBA bits 15:0]
     [0x0000]
     [0x0001]          transfer count = 1 block
     [0x0000]

5. wait_drq() again

6. Read 1024 × u16 from port 0x170 → 2048 bytes into buf

7. wait_not_busy(): spin until BSY=0

Returns false if the device is absent, times out, or signals an error. write_sector is not implemented (no-op).

Probing (`Iso9660::probe`)

Iso9660::probe() returns Some(Iso9660) if:

atapi.read_block(16, buf) succeeds (LBA 16 = Primary Volume Descriptor).
buf[0] == 0x01 (PVD type byte).
buf[1..6] == b"CD001" (ISO9660 magic).

On success, the root directory location is extracted from the PVD:

PVD offset	Description
158–161	Root directory LBA (little-endian `u32`)
166–169	Root directory size in bytes (little-endian `u32`)

These are stored as root_lba and root_size on the Iso9660 struct.

Directory Records

ISO9660 directory records have a variable-length structure packed directly into 2048-byte blocks:

Offset	Size	Field
0	1	Record length (`rec_len`)
2–5	4	File LBA (little-endian)
10–13	4	File size in bytes (little-endian)
25	1	Flags (bit 1 = directory)
32	1	File name length
33	N	File name bytes

Records shorter than 33 bytes or with rec_len == 0 (padding) indicate the end of usable data in a block.

Special Entries

Name byte	Meaning
`0x00`	`.` (current directory) — skipped
`0x01`	`..` (parent directory) — skipped

Version Suffix Stripping

ISO9660 file names on disc include a version suffix (e.g. FILE.TXT;1). strip_version removes everything from the last ; onward before returning names to callers.

Case Folding

All returned names are lowercased (to_lower). Name matching via names_match is case-insensitive: both sides are uppercased before comparison.

`IsoEntry`

pub struct IsoEntry {
    pub name:     [u8; 32],
    pub name_len: u8,
    pub is_dir:   bool,
    pub lba:      u32,
    pub size:     u32,
}

Returned by list_dir, find, and resolve. The name is lowercased, version-stripped, truncated to 32 bytes.

Operations

List Directory (`list_dir`)

Iterates blocks starting at lba, covering size bytes total. For each valid record: extracts name, LBA, size, and is_dir; copies to out[count]. Skips . and ... Stops at 64 entries or when size bytes are exhausted.

Find Entry (`find`)

Same block iteration as list_dir but performs names_match(stripped_name, query) on every record, returning the first match.

Path Resolution (`resolve`)

resolve(path) splits the path on / and calls find for each component, threading cur_lba/cur_size forward into each subdirectory. Returns None if any component is missing or if a non-final component is not a directory.

An empty path returns a synthetic IsoEntry for the root (root_lba, root_size).

Read File (`read_file`)

Reads blocks sequentially from entry.lba, copying BLOCK_SIZE (2048) bytes per block until entry.size bytes or the caller's buffer is filled. No cluster chain — ISO9660 files are stored in contiguous extents.

Syscall Integration

Syscall	ISO9660 support
`0x20` read file	Yes — dispatched when path resolves under `/mnt/iso`
`0x21` write file	No — ISO9660 paths return `InvalidInput`
`0x22` rename	No
`0x23` delete	No
`0x27` mkdir	No
`0x28` list dir (by cluster)	No — uses FAT12 cluster numbers
`0x2D` list dir (by path)	Yes
`0x2E` chdir	Yes — validates directory exists, sets `path_cluster = 0`

Limits

Resource	Value
Block size	2048 bytes
IDE base address	`0x170` (secondary channel, hardcoded)
Max entries per `list_dir` call	64
Max name length	32 bytes (truncated)
Max path depth	Unlimited (iterative, not recursive)
Write support	None

ISO9660

Hardware: ATAPI PIO (fs/iso9660/block.rs)

I/O Ports

read_block(lba, buf) Sequence

Probing (Iso9660::probe)