gazagnaire.org / ocaml-squashfs
SquashFS compressed filesystem reader in pure OCaml
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README.md

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, lzma, lzo, xz, lz4, and zstd compression
  • Filesystem writer module for creating SquashFS images
  • Pure OCaml, no external dependencies on squashfs-tools

Installation#

Install with opam:

$ opam install squashfs

If opam cannot find the package, it may not yet be released in the public opam-repository. Add the overlay repository, then install it:

$ opam repo add samoht https://tangled.org/gazagnaire.org/opam-overlay.git
$ opam update
$ opam install squashfs

Usage#

let read_image data =
  match Squashfs.of_string data with
  | Error msg -> Fmt.epr "Error: %s@." msg
  | Ok fs -> (
      Fmt.pr "%a@." Squashfs.pp_superblock (Squashfs.superblock fs);
      match Squashfs.readdir fs (Squashfs.root fs) with
      | Error msg -> Fmt.epr "Error: %s@." msg
      | Ok entries ->
          List.iter
            (fun e ->
              Fmt.pr "%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
  • 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

References#

Licence#

MIT License. See LICENSE.md for details.