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Robert Allan JamesandClaude Sonnet 5 af267a52a6 Artemis Milestone 2h: hot-detach -- 2h complete

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

2026-08-25 14:10:05 -04:00

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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.

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.

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