Filesystem: native backend roadmap (btrfs, xfs, f2fs, zfs, bcachefs)

[lamco-office]

Summary

Tracking issue for native filesystem backend support beyond ext4. Each backend is a separate work item; this issue groups them and tracks dependencies.

Backends

• btrfs (Path A) — first priority post-v0.9.0. Required for openSUSE Leap/Tumbleweed, Fedora Workstation defaults. Subvolume semantics (the @-and-@/boot/ pattern observed on openSUSE) must be handled.
• xfs — Fedora Server default; RHEL /boot on xfs is common. Has a Rust crate ecosystem (xfs2 for read-only on no_std worth evaluating).
• f2fs — Android-derived distros, some embedded. Lower priority.
• zfs — Proxmox, FreeBSD, some Ubuntu installs. Out-of-tree, license complications for kernel use but the read path may still be feasible from a bootloader perspective.
• bcachefs — recent kernel-removal news (6.18) reduces ecosystem urgency. Track but deprioritize.

Constraints

• All backends must implement the FsBackend trait (SDS-1 / lamboot-core/src/fs_backend.rs).
• Read-only is sufficient for SDS-3's needs. Write paths are out of scope.
• Backends should run in no_std and pure-safe Rust where possible.

See also

• Boot: SDS-3 native PE loader bypassed on Debian 13 with ext2 /boot #1 — investigation of why linux_legacy is selected on Debian/ext2; closing this tracker does not close Boot: SDS-3 native PE loader bypassed on Debian 13 with ext2 /boot #1 since the root cause may not be filesystem support.
• ext2 native backend support — separate issue, since ext2 is closer to ext4 than the others.

[lamco-office]

Status refresh.

• btrfs — done. Native read backend (lambutter), including LVM-on-btrfs.
• ext2 / ext3 — covered by the ext4-view backend (indirect block maps); no separate backend needed. See Filesystem: native ext2 backend support #4.
• xfs — next native backend, targeted for v1.0. Full design exists (fork-and-port from xfs-fuse, dual MIT/Apache + BSD-2 NOTICE). Tracked separately for milestone visibility.
• zfs / f2fs / bcachefs — deferred to v1.1+ as community-contribution gates. zfs is a formal deferral: clean-room MIT/Apache only, no CDDL imports. Real beneficiaries are Root-on-ZFS bpool / TrueNAS, not Proxmox (which keeps kernels on a FAT ESP).

Checklist:

• btrfs
• ext2/ext3 (via ext4-view)
• xfs (v1.0)
• f2fs (v1.1+, community)
• zfs (v1.1+, community)
• bcachefs (v1.1+, community)