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SchOS/.claude/memory/schfs-btree-phase1.md
Nexoniarz a1c965da1e include: one folder per subsystem, and includes that name it 
Sixty-five headers sat side by side in include/, so `#include "irq.h"`
said nothing about where irq.h was or what it belonged to, and errno.h,
stat.h and fcntl.h at the top shadowed the system's for any host tool
built with -I./include. They are in folders now -- arch/ core/ fs/
dev/ gfx/ net/ uapi/ (and ldls/ for the Linux driver layer) -- and
every include names the folder, as Linux's do: "core/proc.h".

Done mechanically and checked the hard way: the kernel built from this
tree disassembles identically to the one built from the tree before
it. The full image boots, and userland is the same set of programs.
Paths in docs and comments follow; docs/guides/layout.md has a table
of what is where, and tools/fix-includes.py rewrites old-style
includes from the folders in the tree, for code written before this.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
2026-10-23 15:05:12 +02:00

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name description metadata
schfs-btree-phase1 SchFS phase 1 (the CoW B-tree) is built and passing; run `make schfs-test` after touching it
node_type type originSessionId modified
memory project a665e14b-86bd-4b41-a228-51377f3e9225 2026-08-01T20:34:28.236Z

The filesystem is called SchFS — not "SchFS v2". Design: docs/architecture/schfs.md.

Phase 1 is done (2026-08-01): the copy-on-write B-tree exists and passes its torture harness.

  • include/fs/schfs.h — on-disk format: 4096-byte blocks, 24-byte (objectid, type, offset) keys, node header with a self-pointer, uberblock ring.
  • kernel/fs/schfs/btree.{c,h} — portable C against an abstract struct schfs_bdev, so the same code runs on a host file and in the kernel. Not yet linked into the kernel.
  • tools/schfs_test.c — the harness. make schfs-test builds and runs it.

Measured geometry: max inline value 1016 bytes, fanout 84 (internal) / 127 (leaf).

Run make schfs-test after any change to btree.c. It checks against a reference model, verifies structure, simulates a crash by discarding uncommitted writes, and confirms both a bit flip and a misdirected write are detected.

A test-design trap worth remembering: the harness originally used schfs_key_cmp inside its own reference model. Deliberately breaking that function then broke the tree and the oracle identically, and every check still passed — the suite could not fail. The model now has its own ref_key_cmp written out longhand. Mutation-test any new oracle the same way before trusting it.

Known and deliberate: delete does not merge or rebalance underfull nodes. The tree stays correct and sorted; merging is phase 3.

Next: phase 2 (read-only mount of a v2 image), then writes/transaction groups, then extents. Per-pid /proc for ps/top should ride along with that VFS work — see schunix-devfs-procfs.