Crate mkext4 

Deterministic, streaming, pure-Rust ext4 image builder — plus a verification-grade reader.

Identical builder calls with identical Options produce byte-identical images: UUID, htree hash seed, and every timestamp are explicit inputs, and the crate never consults a clock or RNG. Output streams through a RegionSink: every byte of the image is emitted exactly once and is final — all metadata immediately at Layout::writer, file data behind it at ascending offsets.

Example

Build a small image in memory, then read it back:

use mkext4::sink::VecSink;
use mkext4::{FsBuilder, Meta, Options, ROOT};

let epoch = 1_704_067_200;
let mut opts = Options::new(16 << 20, [0x42; 16], epoch);
opts.label = Some("demo".into());
let mut b = FsBuilder::new(opts)?;
let etc = b.mkdir(ROOT, "etc", Meta::new(0o755, 0, 0, (epoch, 0)))?;
let f = b.file(etc, "hostname", Meta::new(0o644, 0, 0, (epoch, 0)), 5)?;

let layout = b.seal()?; // the complete physical layout is frozen here
let mut sink = VecSink::default();
let mut w = layout.writer(&mut sink)?;
w.fill(f, &mut &b"husky"[..])?;
w.finish()?;

// sink.buf now holds a complete ext4 image (e2fsck-clean, mountable).
let fs = mkext4::reader::Fs::open(&sink.buf[..])?;
assert_eq!(fs.read_file(fs.resolve("/etc/hostname")?)?, b"husky");

Layer map (bottom-up):

• csum / dirhash — ext4’s crc32c conventions and the half_md4 directory hash. Zero-allocation, append-style folds over borrowed slices; verified against byte vectors extracted from real mke2fs images.
• spec — on-disk structures with byte-exact decode/encode into caller-provided buffers.
• reader — walks and verifies complete filesystems (the differential oracle against mke2fs, and the round-trip check for the writer).

Re-exports

pub use build::Features;

pub use build::FsBuilder;

pub use build::InodeCount;

pub use build::InodeHandle;

pub use build::Layout;

pub use build::Meta;

pub use build::Options;

pub use build::SparseSeg;

pub use build::SpecialKind;

pub use build::ROOT;

pub use sink::RegionSink;

Modules

build

The builder API: declare a namespace, seal it into a frozen layout, then stream file contents.

csum

ext4 checksum conventions.

dirhash

ext4 directory-name hashing (htree / dir_index).

reader

Verification-grade ext4 reader.

sink

The streaming output contract.

spec

On-disk ext4 structures: byte-exact decode / encode.

Enums

Error

Errors produced by this crate.

Type Aliases

Result

Crate-wide result type.