# disk/

QEMU disk images used for Artemis (block-storage VM) persistence testing.
Mounted via `Makefile.starkernel`'s `ARTDISK` variable (default
`disk/artemis.img`) as a `virtio-blk-pci` device on all three
architectures' kernel QEMU boots — not `scripts/rundisk.sh`, which targets
a separate, currently-unused `disks/` (plural) directory for the *hosted*
VM's `--disk-img=` flag instead.

- `artemis.img` — standard Artemis persistence test disk. **Reformatted
  2026-08-02**: this image had been stuck in a corrupted state (valid
  `LithosAnanke` magic header, but data not matching what
  `ART-READ-TEST` expects) since before this repo's own git history
  begins (`git log` shows it already broken at the initial commit,
  carried over from the pre-split monorepo). Chasing down the resulting
  persistent `FAIL: persist-read` traced to the *data*, not the code —
  the write→reboot→read round trip works correctly on a fresh image
  (see `artemis-debug-roundtrip.img` below). Reformatted by blanking the
  file and letting a normal boot format+write-test it; verified
  `PASS: persist-read` on amd64, aarch64, and riscv64 against the same
  image afterward (cross-arch resume, matching the arch-neutral on-disk
  format `.claude/ARTEMIS.md` specifies).
- `artemis-debug-roundtrip.img` — round-trip regression fixture created
  during that investigation. Known-good: format → self-test → write-test
  → reboot → resume → `PASS: persist-read`, confirmed 3 times in a row.
  Keep this in a passing state; if a future change breaks it, that's a
  real regression, not a stale-fixture artifact like `artemis.img` was.
- `artemis-persist-test.img` — persistence round-trip test image
  (pre-existing; history/state not re-verified during the above
  investigation).
- `artemis-poison.img` — a separate test image (exact scenario not
  documented elsewhere in the repo as of this writing; name suggests an
  adversarial/corruption test, not confirmed).
- `artemis-unrecognized-test.img` — exercises `ART-HALT-UNRECOG`
  (`.claude/ARTEMIS.md` acceptance criterion #6). **Regenerated
  2026-08-02**: the previous copy of this file had itself been silently
  reformatted by a since-fixed bug in the *generic* block subsystem
  (`src/block_subsystem.c`) — it carried a valid low-level `'STFR'`/v2
  header despite being meant to represent foreign disk content, direct
  forensic evidence of the bug described in `.claude/ARTEMIS.md`'s
  Build Status item 6. Regenerated as 30MB of a repeating
  `POISON-UNRECOGNIZED-DISK-TEST-FIXTURE--NOT-BLANK-NOT-STFR-NOT-ARTEMIS--`
  ASCII pattern — deliberately neither blank, nor the block subsystem's
  own `'STFR'` magic, nor Artemis's `"ARTEMIS\0"` marker. Verified on
  amd64 and riscv64 post-fix: boot correctly halts
  (`ARTEMIS HALT: unrecognized disk content`) and the file's sha256 is
  now byte-for-byte identical before and after boot. Keep this fixture
  in this poisoned state — if a future change makes its sha256 change
  across a boot, that is exactly the regression this fixture exists to
  catch.

Note on incidental header churn: `artemis.img` picks up a few changed
header bytes on every ordinary boot even though no user data changes —
`blk_subsys_attach_device()` always records a fresh `mounted_time` on a
successfully recognized disk, which gets flushed at shutdown. This is
expected bookkeeping, not a bug; revert it before committing rather than
carrying timestamp noise in git history.

- `usb-thumbdrive-test.img` — 64MB raw image backing a QEMU `usb-storage`
  device attached to the xHCI controller's bus (`xhci0.0`) for Milestone 2e/
  2h hotplug testing, added 2026-08-22. Blank (all zero) — `blkio_usb.c` +
  `blk_subsys_attach_device()` wiring (Milestone 2h, done 2026-08-25) attach
  it as `BLK_FMT_PROVISIONAL` every time, which is the intended, exercised
  state; not yet `BLK_FMT_FORMATTED` via `BLK-CONFIRM-FORMAT`.
- `usb-thumbdrive-test2.img` — 64MB raw image, added 2026-08-25 for
  Milestone 2h hot-detach/re-attach verification. Filled with a repeating
  `HOTDETACH-REATTACH-FIXTURE-2026-08-25--` ASCII pattern, deliberately
  distinguishable from `usb-thumbdrive-test.img`'s all-zero content — the
  point is proving a block read *after* detaching `usb-thumbdrive-test.img`
  and re-attaching this one actually returns this pattern rather than
  silently replaying the old device's cached (all-zero) content, which is
  exactly the class of bug a same-LBN-range device swap can cause if the
  VM block window cache (`vm->blk_vm_cbuf[]`) isn't re-validated on a hit.
- `artemis-reloc-test.img` — 64MB raw image, added 2026-08-25 for single-block
  relocation (`RELOCATE-BLOCK`) persistence verification. Blank at creation;
  a genuinely *fresh* volume was required (not `artemis.img`) because
  relocation-table capacity (`reloc_start`/`reloc_devblocks` in
  `blk_volume_meta_t`) is only reserved by `blk_compute_fresh_geometry()` on
  a fresh format — `artemis.img` predates the feature and correctly reads
  back `reloc_devblocks=0` from what was previously unused header padding.
  Attach via `make -f Makefile.starkernel ARTDISK=disk/artemis-reloc-test.img
  ...` (the Makefile's `ARTDISK` var is `?=`-overridable). Not yet
  `BLK-CONFIRM-FORMAT`-committed in the repo copy — commit that step live if
  reusing this fixture for further reloc-table testing.

**Convention, standing as of 2026-08-22: every virtual disk/thumb-drive image
used for testing — Artemis persistence disks above, and USB Mass Storage
backing images alike — lives in this directory and is a tracked, committed
file, never scratchpad.** This was already `artemis.img`'s convention;
`usb-thumbdrive-test.img` and any future USB test images follow the same
rule. Confirmed no `.gitignore` in this repo excludes `disk/*.img`.

These are regenerable QEMU raw disk images, not source — see
`.claude/ARTEMIS.md` for the storage model they exercise.