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
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 (validLithosAnankemagic header, but data not matching whatART-READ-TESTexpects) since before this repo's own git history begins (git logshows it already broken at the initial commit, carried over from the pre-split monorepo). Chasing down the resulting persistentFAIL: persist-readtraced to the data, not the code — the write→reboot→read round trip works correctly on a fresh image (seeartemis-debug-roundtrip.imgbelow). Reformatted by blanking the file and letting a normal boot format+write-test it; verifiedPASS: persist-readon amd64, aarch64, and riscv64 against the same image afterward (cross-arch resume, matching the arch-neutral on-disk format.claude/ARTEMIS.mdspecifies).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 likeartemis.imgwas.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— exercisesART-HALT-UNRECOG(.claude/ARTEMIS.mdacceptance 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 repeatingPOISON-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 QEMUusb-storagedevice 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 asBLK_FMT_PROVISIONALevery time, which is the intended, exercised state; not yetBLK_FMT_FORMATTEDviaBLK-CONFIRM-FORMAT.usb-thumbdrive-test2.img— 64MB raw image, added 2026-08-25 for Milestone 2h hot-detach/re-attach verification. Filled with a repeatingHOTDETACH-REATTACH-FIXTURE-2026-08-25--ASCII pattern, deliberately distinguishable fromusb-thumbdrive-test.img's all-zero content — the point is proving a block read after detachingusb-thumbdrive-test.imgand 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.