squashfs#

SquashFS compressed filesystem reader in pure OCaml.

Overview#

SquashFS is a compressed read-only filesystem commonly used for:

• Linux initramfs/initrd images
• Container images (Docker, Snap packages)
• Live CD/USB distributions
• Embedded systems

This library provides read-only access to SquashFS 4.0 images.

Features#

• Read SquashFS superblock and metadata
• Navigate directory structure
• Read file contents
• Read symbolic link targets
• Supports gzip compression (zstd planned)
• Pure OCaml, no external dependencies on squashfs-tools

Installation#

opam install squashfs

Usage#

(* Open a SquashFS image *)
let data = (* read image file *) in
match Squashfs.of_string data with
| Error msg -> Printf.eprintf "Error: %s\n" msg
| Ok fs ->
    (* Print superblock info *)
    Format.printf "%a@." Squashfs.pp_superblock (Squashfs.superblock fs);

    (* List root directory *)
    match Squashfs.readdir fs (Squashfs.root fs) with
    | Error msg -> Printf.eprintf "Error: %s\n" msg
    | Ok entries ->
        List.iter (fun e ->
          Format.printf "%s (%a)@." e.Squashfs.name
            Squashfs.pp_file_type e.Squashfs.file_type
        ) entries

API#

Opening Images#

• Squashfs.of_string - Open from string data
• Squashfs.of_reader - Open from bytesrw reader

Navigation#

• Squashfs.root - Get root directory inode
• Squashfs.readdir - List directory entries
• Squashfs.lookup - Look up entry by name
• Squashfs.resolve - Resolve path to inode

File Operations#

• Squashfs.read_file - Read file contents
• Squashfs.read_link - Read symlink target

Inode Properties#

• Squashfs.inode_type - File type
• Squashfs.inode_mode - Permission bits
• Squashfs.inode_size - File size
• Squashfs.inode_mtime - Modification time

Related Work#

• squashfs-tools - Reference C implementation
• go-squashfs - Go implementation
• rust-squashfs - Rust implementation

References#

• SquashFS Specification
• Linux Kernel Documentation

Licence#

MIT License. See LICENSE.md for details.