Robert Allan JamesandClaude Sonnet 5
af267a52a6
blk_subsys_detach_device() (block_subsystem.c) walks the device chain, refuses removal of anything but the current tail (a mid-chain removal would corrupt every later slot's start_lbn -- this architecture's own doc already argues USB stays last specifically to avoid that), unlinks, shrinks total_user_lbn, closes and frees the slot. Discards rather than flushes dirty state -- the device is physically gone by the time this runs (PORTSC disconnect only). Trigger wiring mirrors the attach path: bot_msc_attached (set only once attach actually succeeds) gates a new bot_msc_detach_pending flag set at PORTSC disconnect (not Disable Slot completion, which is conditionally skipped and would miss concurrent connect/disconnect pairs), consumed in sk_repl_idle(). Advisor flagged the real hazard ahead of time: block_words.c's VM block window (blk_vm_lbn[]/blk_vm_cbuf[]) can go stale across a detach then a same-LBN re-attach, and suggested a pointer-identity re-check in blk_vm_load() as a minimal fix. That fix was implemented, then directly falsified by its own designed-for-this test: attach a blank device, read a block (populating the cache), detach, re-attach a device with distinct content at the identical LBN, read again -- served stale content from the first device. Root cause, confirmed live: glibc's allocator hands free(slot) straight back to the very next same-size calloc(), so the "fresh" and stale pointers were bitwise identical despite being two different devices. Fixed properly with a monotonic blk_subsys_epoch() counter (bumped on every attach/detach) checked by a new blk_vm_check_epoch() helper at the one choke point (blk_vm_find(), plus blk_vm_flush_all() which reads the same arrays directly) that covers every path touching the window cache -- unfooled by address reuse. Verified live with a new disk/usb-thumbdrive-test2.img fixture (distinct content from the existing blank test image): attach A, read (cache hit populated), detach, re-attach B at the same LBN, read again -- correctly ran a fresh device read and returned B's real content, not A's stale cached zeros. The failing pointer-comparison attempt's own capture log kept as evidence, not deleted. All three architectures re-verified clean. FABRIC-2.md Section X 2h marked complete -- enumeration through hot-detach all live and verified; only WRITE(10) (2g's own still-open item) remains unimplemented in the driver, not blocking anything here. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01CXjAPTEKrgY2Mrk25KoLDn
84 lines
5.0 KiB
Markdown
84 lines
5.0 KiB
Markdown
# disk/
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QEMU disk images used for Artemis (block-storage VM) persistence testing.
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Mounted via `Makefile.starkernel`'s `ARTDISK` variable (default
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`disk/artemis.img`) as a `virtio-blk-pci` device on all three
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architectures' kernel QEMU boots — not `scripts/rundisk.sh`, which targets
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a separate, currently-unused `disks/` (plural) directory for the *hosted*
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VM's `--disk-img=` flag instead.
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- `artemis.img` — standard Artemis persistence test disk. **Reformatted
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2026-08-02**: this image had been stuck in a corrupted state (valid
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`LithosAnanke` magic header, but data not matching what
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`ART-READ-TEST` expects) since before this repo's own git history
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begins (`git log` shows it already broken at the initial commit,
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carried over from the pre-split monorepo). Chasing down the resulting
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persistent `FAIL: persist-read` traced to the *data*, not the code —
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the write→reboot→read round trip works correctly on a fresh image
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(see `artemis-debug-roundtrip.img` below). Reformatted by blanking the
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file and letting a normal boot format+write-test it; verified
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`PASS: persist-read` on amd64, aarch64, and riscv64 against the same
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image afterward (cross-arch resume, matching the arch-neutral on-disk
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format `.claude/ARTEMIS.md` specifies).
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- `artemis-debug-roundtrip.img` — round-trip regression fixture created
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during that investigation. Known-good: format → self-test → write-test
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→ reboot → resume → `PASS: persist-read`, confirmed 3 times in a row.
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Keep this in a passing state; if a future change breaks it, that's a
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real regression, not a stale-fixture artifact like `artemis.img` was.
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- `artemis-persist-test.img` — persistence round-trip test image
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(pre-existing; history/state not re-verified during the above
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investigation).
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- `artemis-poison.img` — a separate test image (exact scenario not
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documented elsewhere in the repo as of this writing; name suggests an
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adversarial/corruption test, not confirmed).
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- `artemis-unrecognized-test.img` — exercises `ART-HALT-UNRECOG`
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(`.claude/ARTEMIS.md` acceptance criterion #6). **Regenerated
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2026-08-02**: the previous copy of this file had itself been silently
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reformatted by a since-fixed bug in the *generic* block subsystem
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(`src/block_subsystem.c`) — it carried a valid low-level `'STFR'`/v2
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header despite being meant to represent foreign disk content, direct
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forensic evidence of the bug described in `.claude/ARTEMIS.md`'s
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Build Status item 6. Regenerated as 30MB of a repeating
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`POISON-UNRECOGNIZED-DISK-TEST-FIXTURE--NOT-BLANK-NOT-STFR-NOT-ARTEMIS--`
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ASCII pattern — deliberately neither blank, nor the block subsystem's
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own `'STFR'` magic, nor Artemis's `"ARTEMIS\0"` marker. Verified on
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amd64 and riscv64 post-fix: boot correctly halts
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(`ARTEMIS HALT: unrecognized disk content`) and the file's sha256 is
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now byte-for-byte identical before and after boot. Keep this fixture
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in this poisoned state — if a future change makes its sha256 change
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across a boot, that is exactly the regression this fixture exists to
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catch.
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Note on incidental header churn: `artemis.img` picks up a few changed
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header bytes on every ordinary boot even though no user data changes —
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`blk_subsys_attach_device()` always records a fresh `mounted_time` on a
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successfully recognized disk, which gets flushed at shutdown. This is
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expected bookkeeping, not a bug; revert it before committing rather than
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carrying timestamp noise in git history.
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- `usb-thumbdrive-test.img` — 64MB raw image backing a QEMU `usb-storage`
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device attached to the xHCI controller's bus (`xhci0.0`) for Milestone 2e/
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2h hotplug testing, added 2026-08-22. Blank (all zero) — `blkio_usb.c` +
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`blk_subsys_attach_device()` wiring (Milestone 2h, done 2026-08-25) attach
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it as `BLK_FMT_PROVISIONAL` every time, which is the intended, exercised
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state; not yet `BLK_FMT_FORMATTED` via `BLK-CONFIRM-FORMAT`.
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- `usb-thumbdrive-test2.img` — 64MB raw image, added 2026-08-25 for
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Milestone 2h hot-detach/re-attach verification. Filled with a repeating
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`HOTDETACH-REATTACH-FIXTURE-2026-08-25--` ASCII pattern, deliberately
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distinguishable from `usb-thumbdrive-test.img`'s all-zero content — the
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point is proving a block read *after* detaching `usb-thumbdrive-test.img`
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and re-attaching this one actually returns this pattern rather than
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silently replaying the old device's cached (all-zero) content, which is
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exactly the class of bug a same-LBN-range device swap can cause if the
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VM block window cache (`vm->blk_vm_cbuf[]`) isn't re-validated on a hit.
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**Convention, standing as of 2026-08-22: every virtual disk/thumb-drive image
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used for testing — Artemis persistence disks above, and USB Mass Storage
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backing images alike — lives in this directory and is a tracked, committed
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file, never scratchpad.** This was already `artemis.img`'s convention;
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`usb-thumbdrive-test.img` and any future USB test images follow the same
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rule. Confirmed no `.gitignore` in this repo excludes `disk/*.img`.
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These are regenerable QEMU raw disk images, not source — see
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`.claude/ARTEMIS.md` for the storage model they exercise.
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