[RFC PATCH 0/10] ftrfs: Fault-Tolerant Radiation-Robust Filesystem

[Aurelien DESBRIERES]

From: Aurélien DESBRIERES <aurelien@xxxxxxxxxxxx>

This RFC introduces FTRFS, a new Linux filesystem designed for dependable
storage in radiation-intensive environments, targeting embedded Linux systems
operating in space or other harsh conditions.

FTRFS was originally described in:

  Fuchs, C.M., Langer, M., Trinitis, C. (2015).
  FTRFS: A Fault-Tolerant Radiation-Robust Filesystem for Space Use.
  ARCS 2015, LNCS vol 9017, Springer.
  https://doi.org/10.1007/978-3-319-16086-3_8

This implementation is an independent open-source realization of the
concepts described in that paper, developed for the Linux kernel.

== Design ==

FTRFS provides three layers of data integrity:

  - CRC32 per block and per inode (hardware-accelerated via crc32_le)
  - Reed-Solomon FEC (encoder implemented, decoder planned)
  - EDAC-compatible error tracking

On-disk layout:

  Block 0        : superblock (magic 0x46545246, CRC32-protected)
  Block 1..N     : inode table (128 bytes/inode, CRC32 per inode)
  Block N+1..end : data blocks (CRC32 + RS FEC per block)

Inodes use direct addressing (12 direct block pointers) plus single
and double indirection. Directory entries are fixed-size (268 bytes)
stored in direct blocks.

== Current Status ==

  - Superblock: mount/umount, CRC32 validation            [done]
  - Inodes: read with CRC32 verification                  [done]
  - Directories: readdir, lookup                          [done]
  - Files: read via generic page cache helpers            [done]
  - Allocator: in-memory bitmap for blocks and inodes     [done]
  - Write path: create, mkdir, unlink, rmdir, link        [done]
  - Reed-Solomon: encoder done, decoder planned           [partial]
  - xattrs / SELinux                                      [planned]
  - fsck.ftrfs                                            [planned]
  - Indirect block support for large files                [planned]

== Validation ==

FTRFS has been validated on arm64 (cortex-a57) running Linux 7.0-rc7,
built with Yocto Styhead (5.1), deployed as a data partition in a
3-node Slurm HPC cluster on KVM/QEMU:

  insmod ftrfs.ko  ->  module loaded
  mount -t ftrfs /dev/vdb /mnt  ->  success
  ls /mnt  ->  returns empty directory correctly

Compile-tested on x86_64 with Linux 7.0 (this series).
checkpatch.pl: 0 errors on all patches.

== Feedback Requested ==

This is an RFC. Feedback is welcome on:

  1. On-disk format: is the superblock/inode layout reasonable?
  2. Directory entry design: fixed 268-byte entries vs. variable length
  3. Reed-Solomon: use lib/reed_solomon or keep custom GF(2^8) tables?
  4. Allocator: in-memory bitmap vs. dedicated on-disk bitmap block
  5. Any VFS API misuse or missing locking

The code is also available at:
  https://github.com/roastercode/FTRFS

Aurélien DESBRIERES (10):
  ftrfs: add on-disk format and in-memory data structures
  ftrfs: add superblock operations
  ftrfs: add inode operations
  ftrfs: add directory operations
  ftrfs: add file operations
  ftrfs: add block and inode allocator
  ftrfs: add filename and directory entry operations
  ftrfs: add CRC32 checksumming and Reed-Solomon FEC skeleton
  ftrfs: add Kconfig, Makefile and fs/ tree integration
  MAINTAINERS: add entry for FTRFS filesystem

 MAINTAINERS          |   6 +
 fs/Kconfig           |   1 +
 fs/Makefile          |   1 +
 fs/ftrfs/Kconfig     |  49 +++
 fs/ftrfs/Makefile    |  16 +
 fs/ftrfs/alloc.c     | 251 +++++++++++++++
 fs/ftrfs/dir.c       | 132 ++++++++
 fs/ftrfs/edac.c      |  84 +++++
 fs/ftrfs/file.c      |  25 ++
 fs/ftrfs/ftrfs.h     | 168 ++++++++++
 fs/ftrfs/inode.c     | 103 +++++++
 fs/ftrfs/namei.c     | 428 +++++++++++++++++++++++++++
 fs/ftrfs/super.c     | 274 ++++++++++++++++
 13 files changed, 1538 insertions(+)

Signed-off-by: Aurélien DESBRIERES <aurelien@xxxxxxxxxxxx>