lamzfs

A no_std + alloc, read-only ZFS pool reader for UEFI bootloaders.

lamzfs imports a ZFS pool over a plain byte source, walks to one dataset, and reads its files — enough for a bootloader to find a kernel and initramfs without the OpenZFS kernel module, without std, and without a GPL UEFI driver. The motivating target is Ubuntu / Debian root-on-ZFS, which keep a simple bpool boot pool. Read-only by construction: there is no write path and no BlockWrite.

Scope (v0.1)

Supported:

Topologies: single disk, mirror, and single-parity RAID-Z1 (including degraded reads that reconstruct a missing/corrupt column from parity).
Compression: off, zle, lzjb, lz4, gzip, zstd (each a feature).
Checksums: Fletcher-2/4 and SHA-256 (scalar).
The full read walk: vdev label → uberblock → MOS → DSL → dataset → ZPL → ZAP directories → indirect block-pointer tree (sparse-file aware).

Out of scope: any write path, encryption, RAID-Z2/3, dRAID, and gang blocks (each rejected with a typed error).

Usage

Implement BlockRead over your device, then import and read:

use lamzfs::{BlockRead, PoolMember, Zfs};

# struct Disk;
# impl BlockRead for Disk {
#     type Error = ();
#     fn read_at(&mut self, _off: u64, _buf: &mut [u8]) -> Result<(), ()> { Ok(()) }
# }
# fn members() -> Vec<PoolMember<Disk>> { Vec::new() }
let mut zfs = Zfs::import(members())?;          // one PoolMember per vdev member
println!("pool {} ({:#x})", zfs.pool_name(), zfs.pool_guid());

// Dataset path = child-directory components under the pool root; the second
// argument is the directory within that dataset (empty = its root).
for entry in zfs.read_dir(&["BOOT", "default"], &[])? {
    println!("{:?} {}", entry.kind, entry.name);
}
let kernel = zfs.read(&["BOOT", "default"], &["vmlinuz"])?;
# Ok::<(), lamzfs::Error>(())

See examples/zfsdump.rs for a runnable host tool.

Basis

The on-disk decoders are vendored from rzfs, electing the MIT half of its GPL-2.0 OR MIT dual license — a clean-room reader, not GPL kernel/userspace source. The orchestration (pool import, vdev routing, dataset walk, path resolve, file read) is new lamzfs code. The crate is scalar-only and #![forbid(unsafe_code)]. See NOTICE for attribution.

License

Licensed under either of

Apache License, Version 2.0 (LICENSE-APACHE)
MIT license (LICENSE-MIT)

at your option. Vendored upstream portions retain their own terms (see NOTICE).

Contribution