GEFS for NetBSD

A native NetBSD port of GEFS, the copy-on-write Bε-tree file system of 9front (by Ori Bernstein): a kernel file system (vfsops, vnode operations, UBC), not FUSE, that NetBSD boots from and runs its root on, and that keeps a laptop's disk idle whenever nothing changes.

Design, status and what the port taught: doc/DESIGN.org. A plan for a more frugal write policy within the same format: doc/GEFSPLUS.org. The 9front sources were imported unmodified in the first commit; every change to them since is marked NetBSD: in the code.

Layout

sys/fs/gefs/            the core (from 9front) and the NetBSD kernel side
  compat/               Plan 9 headers: u.h, libc.h, avl.h, fcall.h
  p9fmt.c p9err.c       print(2) and error handling, kernel and userland
  p9kern.c p9user.c     locks, memory, time, device I/O for each
  ops.c                 POSIX operations on the core (create, rename, ...)
  sync.c                commits, labels, snapshots, sweeping, the reserve
  snapadm.c             adm/ctl commands, status, snapshot schedules
  gefs_vfsops.c         devices, mounts, sync, admin ioctl, mountroot
  gefs_vnops.c          vnode operations, UBC through bmap/strategy
  gefs_work.c           the mutator and reader threads, page I/O queue
  files.gefs            to build GEFS into a kernel
sys/modules/gefs        the module
sys/lib/libsa/gefs.c    read-only gefs for the boot loaders (efiboot)
sbin/mount_gefs         mount helper, mount_gefs(8)
sbin/gefs               gefs(8): newfs_gefs, fsck_gefs, snapshots
patches/                changes to NetBSD's own files (efiboot, the tree)
tests/gefstest.c        core and operations tests, userland
tests/fsxlite.c         random operations against a copy in memory
tests/sagefs/           the boot loader's reader, in userland

Building

Userland tools and tests (NetBSD or Linux, GCC):

cd sbin/gefs && make -f Makefile.host
truncate -s 512M /tmp/t.img && ./gefstest /tmp/t.img

The module, in a NetBSD 11 source tree (sys/fs/gefs and sys/modules/gefs linked or copied into /usr/src/sys):

cd /usr/src/sys/modules/gefs && make && modload ./gefs.kmod
newfs_gefs /dev/rdk1 && mount -t gefs /dev/dk1 /mnt

Built in: add include "fs/gefs/files.gefs" (or apply patches/netbsd-11-tree.diff) and file-system GEFS to a kernel configuration. The EFI boot loader with gefs: patches/netbsd-11-efiboot.diff plus sys/lib/libsa/gefs.[ch].

Using it

newfs_gefs /dev/rdk1                   # retention 60@m 24@h 14@d
mount -t gefs /dev/dk1 /mnt
gefs snap /mnt main before-upgrade     # a snapshot, taken now
gefs fork /mnt empty obj               # a new empty mutable label
gefs retain /mnt obj none
mount -t gefs -o snap=obj /dev/dk1 /usr/obj
gefs status /mnt                       # usage, retention, labels
mount -t gefs -o ro,snap=before-upgrade /dev/dk1 /n/old

See gefs(8) and mount_gefs(8).

State

Works in a NetBSD 11.0 VM: mount, all file types, reads and writes through UBC (mmap, exec), rename, hard links, symlinks, device nodes, fifos, relatime, fsync, crash consistency (the last commit survives), snapshots and forks (taken, deleted, mounted next to main, taken on a schedule only when something changed), booting under UEFI from a disk with only an ESP and a gefs partition, a full file system (rm and unmount work, write says ENOSPC), low memory, and an idle mount writes nothing. Not yet: NFS export (gefs has no index from inode number to entry), ctime (reported as mtime), extended attributes.