Artemis genesis stamp: fix a BAM-corrupting offset before it ever ran (FABRIC-3.md §XXVI follow-on, Step 3)
Step 3: one-time artemis_sig_t genesis stamp, written once
kernel_main.c's virtio-blk path confirms Artemis's own disk, so the disk
image is later recognizable generically (repl.c's idle-loop USB-MSC scan,
built in the prior commit) regardless of which bus found it.
Correction made before this ever touched the real disk: the signature's
first design (committed in 29b6789) placed it at a fixed bottom-of-device
forth-block (4, devblock 1) -- copying homeblocks_sig_t's own convention,
which is safe for a raw identity thumbdrive but not for Artemis's own
disk. Artemis's disk is block_subsystem.c's own STFR/v2-formatted volume:
devblock 0 holds that format's header and devblock 1 is the FIRST
DEVBLOCK OF THE LIVE BAM (blk_compute_fresh_geometry(): bam_start = 1).
The original design would have overwritten Artemis's live allocation map
on the very first real boot. Caught via direct cross-reference against
block_subsystem.c before the genesis-stamp call site was ever run against
the real image -- no corruption occurred.
Fixed by moving the header to a fixed offset from the END of the device
instead (ARTEMIS_SIG_DEVBLOCK_FROM_TOP=64), the same top-of-device region
block_subsystem.c's own meta_fence_blocks reservation (128 devblocks)
already carves out for system metadata, and where Zuse's genesis marker/
eligibility list already live -- but computed independently via
blkio_info() rather than through blk_meta_zone_*(), since that accessor
needs an already-attached, format-detected slot, which is exactly the
state pre-attach generic discovery doesn't have yet. Picked well clear of
Zuse's two tenants (devblock_from_top 0 and 1+, open-ended) so the two
subsystems' independent math can never collide.
Also reordered kernel_main.c: rng_init() now runs before the Artemis
virtio-blk block (was after) -- the genesis stamp needs rng_get_bytes()
for disk_uuid, and the original order would have failed the stamp on
every boot.
Verified live: booted amd64 against the real disk/artemis.img twice --
first boot logs "Artemis: genesis signature stamped" (confirmed blank at
the target offset beforehand via a host-side read), second boot on the
now-stamped image logs no re-stamp (idempotent, CRC/read-back verified)
-- both boots and aarch64/riscv64 (against the same now-stamped image)
all still report "Artemis: 22998 data blocks" / "PASS: persist-read"
unchanged, confirming the BAM and data pool were never touched.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EXieurDfDSsDFdnSyusuWo
This commit is contained in:
Robert Allan James
co-authored by
Claude Sonnet 5
Claude Sonnet 5
parent
29b6789860
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