partitions

Pure-Rust partition-table probe and filesystem-magic sniffer over any random-access block source.

What it does

Given a BlockRead (a tiny trait: read_at(offset, buf) + size_bytes()), this crate tells you:

1. Is there a GPT or MBR partition table?
2. What partitions exist? (start, length, type, label, UUID)
3. For each partition, what filesystem signature is at the start?

It does not mount anything, decode files, or write — it's a probe.

Status

Read side (probe + sniff)

• GPT primary header (signature, CRC32 validation, entry array)
• GPT backup header read + validate, with primary/backup mismatch reporting (gpt::parse_backup, gpt::validate_backup returning BackupStatus::Ok / Mismatch)
• MBR with GPT-protective fallthrough
• FS sniff: ext2/3/4, NTFS, exFAT, FAT16, FAT32, HFS+, APFS, Linux swap, ISO 9660, SquashFS
• SliceReader adapter — rebases offsets on a sub-range of any BlockRead (planned to move into am-fs-core since slicing is a generic block-layer concern; this crate will re-export for backwards compatibility)
• C ABI for FFI (partitions_probe, partitions_count, partitions_table_kind, partitions_get, partitions_sniff, partitions_open_slice, partitions_list_free; header in include/partitions.h)
• LVM / LUKS / mdraid detection
• Logical-partition (extended MBR) chain walking

Write side (table mutation)

• GPT writer: protective MBR + primary header + entry array + backup mirror at end of disk, all CRCs computed correctly (gpt_write::write_gpt)
• MBR writer (mbr::write_mbr, four primary entries)
• Mutation API: add / remove / resize over an in-memory partition set, with 1 MiB alignment and a first-fit free-space finder (PartitionSet)
• commit(&dev) semantics — writes happen on commit, not on mutation
• Round-trip tests: probe → mutate → commit → re-probe matches intent (tests/mutation.rs)
• C ABI for the writer — the existing partitions_* handle stays read-only; a writable handle is a follow-up
• Optional with_boot_code variant of the MBR / protective-MBR writer for legacy BIOS boot

Use

use partitions::{probe, sniff, BlockRead, FileBlock};

let dev = FileBlock::open("disk.img")?;
let parts = probe(&dev)?;
for p in &parts {
    let kind = sniff(&dev, p)?;
    println!("{} bytes @ {} -> {:?}", p.length, p.start, kind);
}

Layout

src/
  lib.rs        public API + BlockRead/BlockDevice + FileBlock + SliceReader
  error.rs      Error / Result
  gpt.rs        GPT header + entry array parser, backup-header validator
  gpt_write.rs  GPT writer (protective MBR + primary + backup, CRCs)
  mbr.rs        MBR parser + writer
  mutation.rs   PartitionSet — in-memory add/remove/resize + commit
  sniff.rs      filesystem magic-byte sniffer
  probe.rs      top-level dispatch (try GPT, fall back to MBR)
tests/
  fixtures.rs   hand-built GPT/MBR + sniff fixtures
  mutation.rs   round-trip mutate/commit/re-probe tests

License

MIT.