lamlvm

Read-only LVM2 Logical Volume reader for no_std environments — primarily UEFI bootloaders that need to mount a filesystem from a logical volume without pulling in a userspace LVM stack.

Vendored + modernized fork of main--/rust-lvm2. See PROVENANCE.md for the origin story and the full list of changes from upstream.

What it does

Given any embedded_io::Read + Seek source that holds an LVM2 Physical Volume (typically a block device or partition):

Parses the PV label (LABELONE signature at sector 1) and PV header.
Reads the Volume Group metadata text (LVM2 format-text in the metadata area).
Enumerates the Logical Volumes in the VG.
Returns each LV as an OpenLV that itself implements embedded_io::Read + Seek, with offsets mapped from LV space to PV space via the segment table.

Existing filesystem crates (ext4 readers, btrfs readers, etc.) plug onto the OpenLV byte stream unchanged — they don't know or care whether bytes come from a partition directly or from an LV sitting on top of a partition.

What it doesn't do

Only linear LVs on a single PV are supported. Striped, mirrored (RAID-1/5/6), thin pool, snapshot, and cache LVs all error with a diagnostic. This covers the canonical layout used by Proxmox VE and most default single-disk LVM installs. See PROVENANCE.md for the full coverage matrix and the rationale for the narrow scope.

This is a reader only. It never writes to a PV.

Usage sketch

use embedded_io::{Read, Seek};
use lamlvm::Lvm2;

// `reader` is anything implementing embedded_io::Read + Seek over the PV's
// bytes — a block device, a partition, or an image file (std callers can
// wrap a File with the embedded-io-adapters crate). Lvm2::open and
// open_lv_by_name each borrow it in turn.
fn read_root_lv<R: Read + Seek>(mut reader: R) -> Result<(), lamlvm::Error> {
    let lvm = Lvm2::open(&mut reader)?;

    // open_lv_by_name returns None when the VG has no LV by that name.
    if let Some(open_lv) = lvm.open_lv_by_name("root", &mut reader) {
        // `open_lv` implements embedded_io::Read + Seek. Hand it to any
        // filesystem reader (e.g. ext4-view) unchanged — it can't tell the
        // bytes come from an LV rather than from a bare partition.
        let _ = open_lv;
    }
    Ok(())
}

A worked example walking ext4 on top of a real LV is in examples/walk_ext4_on_lv.rs.

no_std

Set default-features = false for full no_std operation. alloc is required (the metadata-text parse path allocates).

License