lamfold-cramfs 0.1.0

no_std clean-room cramfs reader — the lamfold compressed-ROM legacy frontend (per-page zlib)
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  • Source code size: 18.31 kB This is the summed size of all the files inside the crates.io package for this release.
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lamfold-cramfs

The cramfs frontend of the lamfold read-only media stack — clean-room Compressed ROM filesystem (per-page zlib).

Reads over a lamfold::BlockSource and implements lamfold::FoldFrontend. cramfs is the small per-page-zlib read-only format for embedded firmware and rescue images — compressed like squashfs, but with a far terser structure (a 12-byte bitfield inode, a flat per-page block index) for where squashfs is too heavy. Spec: the lamfold design spec §4.

Status

Layer State
Superblock (magic 0x28CD3D45, root inode at byte 64) ✅ done + tested
Inodes (12-byte bitfield: mode/uid, size/gid, namelen/offset) ✅ done + tested
Directory records (inode + name run over the inode size) ✅ done + tested
Per-page zlib block index (u32 end-offsets → substrate Codec::Zlib, hole zero-fill) ✅ done + tested
Symlinks via read_link (zlib-stored target) ✅ done + tested
big-endian images, EXT_BLOCK_POINTERS extension rejected Unsupported (not mis-read)

Complete. Verified against a real mkcramfs (cramfs-tools) image, cross-checked with cramfsck: probe, tree walk, a 300 KB file across 74 zlib-compressed pages (full + partial across a page boundary + EOF), a nested directory, and a symlink. Builds default + --no-default-features (no_std), clippy -D warnings clean, #![forbid(unsafe_code)] — every page inflated through the shared substrate codec.

Clean-room posture

Derived only from the kernel cramfs format docs (cramfs_fs.h is the on-disk structure). The GPL-2 fs/cramfs driver is fenced off. The upstream cramfs crate is unbuildable, so there was nothing permissive to reuse.

Build / test

cargo build
cargo test                                   # walks tests/fixtures/cramfs.img
cargo build --no-default-features            # no_std check

MIT OR Apache-2.0.