lamxfs

A no_std, read-only XFS filesystem reader for UEFI bootloaders and other pre-OS contexts. Clean-room, memory-safe Rust (#![forbid(unsafe_code)]).

lamxfs exists so a bootloader (LamBoot in particular) can read kernels, initrds, and boot configuration directly from XFS /boot and / partitions — the default on RHEL 9, Rocky 9, AlmaLinux 9, Oracle Linux 9, CentOS Stream, and Amazon Linux — without a GPL UEFI filesystem driver (unsignable under Microsoft Secure Boot), without std, and without the Linux kernel.

It is the XFS counterpart to ext4-view and the Lamco-authored lambutter (btrfs), with a deliberately matching API so a consumer's filesystem adapter is one-for-one across the read-only family.

Scope

Read-only, single data device. There is no write path and no BlockWrite trait — read-only by construction.

Supported on-disk layout (the subset present on stock RHEL-family installs):

Refused with a typed error (never mis-read): realtime device, external log, in-progress mkfs, unknown incompat feature, per-file encryption.

Usage

use lamxfs::{Xfs, Path, BlockRead};

let mut fs = Xfs::open(reader, device_size_bytes)?;       // validates the superblock
let cfg = fs.read_file(Path::new(b"/boot/loader/entries/rocky.conf"))?;
let ino = fs.resolve(Path::new(b"/boot/vmlinuz-6.1.0"))?;
let mut buf = [0u8; 1 << 20];
let n = fs.read_file_at(&ino, 0, &mut buf)?;              // streaming (PE-loader path)
for e in fs.read_dir(Path::new(b"/boot"))? { /* … */ }

read_file caps its up-front allocation at MAX_FILE_BYTES (256 MiB): a hostile inode can declare a huge di_size while occupying no extents, so the size field is never trusted to drive an allocation. read_file_at streams into a caller-sized buffer and is unaffected.

You implement BlockRead (one method, read_at) over your device — the same shape as lambutter::BlockRead.

Safety & hardening

#![forbid(unsafe_code)]. Every on-disk count, offset, and shift is bounds- and range-checked before use, so malformed or hostile media yields a typed error rather than a panic, out-of-bounds read, or denial-of-boot allocation. Validated by fuzzing (cargo +nightly fuzz run fuzz_open / fuzz_walk).

Testing

• Layer A — synthetic-byte unit tests for each parser (cargo test).
• Layer B — oracle tests against real mkfs.xfs images (v5+NREXT64, v5 without NREXT64, v4 legacy): every file is verified against its kernel-produced SHA-256 (tests/oracle.rs; regenerate with tests/fixtures/regenerate.sh).
• Layer C — cargo fuzz targets over arbitrary and seed-mutated volumes.

License

MIT OR Apache-2.0. Clean-room from the public XFS on-disk format; see NOTICE.