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Implement homeblocks_sig_check(): the drive signature check (Phase 8)

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Real, complete verification logic -- not yet wired to any write path.
homeblocks_sig_check(dev, sig_start_fblock, out_sig) reads the 4
consecutive 1KB blkio forth-blocks the 4KB header spans, verifies
magic -> version -> CRC-64 in order, returns HOMEBLOCKS_SIG_OK/_BLANK/
_BAD_VERSION/_BAD_CRC/_READ_ERROR. Reuses block_subsystem.c's existing
CRC-64/ISO (compute_crc64, previously static/file-local, now exposed
via block_subsystem.h) rather than a second CRC implementation --
same algorithm already proven via per-block checksums. Takes the
header's starting block as a plain parameter rather than resolving it
internally: verifies a signature given a location, finding that
location (GPT-partition-relative) stays the caller's job.

Verified against the actual shipped code, not a reimplementation: a
standalone host test links the real homeblocks_sig.c against a fake
in-memory blkio_dev and exercises all four outcomes -- blank media,
a correctly-minted header (round-trips drive_uuid/minted_time_ns), a
flipped CRC, an unrecognized version. All four pass. A full
QEMU-hotplug live test isn't proportionate yet since nothing calls
this function from the live kernel path -- wiring it into the attach
path is the next punch-list item. Clean zero-warning compile and
clean boot on all three architectures confirms no build/link
regression from exposing compute_crc64 and adding the new source
file to every kernel build.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CXjAPTEKrgY2Mrk25KoLDn
This commit is contained in:
Robert Allan James
2026-08-26 07:05:37 -04:00
co-authored by Claude Sonnet 5
parent 10b96870c5
commit 2c45744995
13 changed files with 27292 additions and 6 deletions
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include/block_subsystem.h
+6
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@@ -293,6 +293,12 @@ int blk_get_volume_meta(blk_volume_meta_t *meta);
int blk_set_volume_meta(const blk_volume_meta_t *meta);
/* CRC-64/ISO (poly 0x42F0E1EBA9EA3693), reflected, init/final all-ones --
* exposed for homeblocks_sig.c's drive-signature integrity check, which
* needs the exact same algorithm this file already uses for per-block
* checksums rather than a second, duplicate CRC implementation. */
uint64_t compute_crc64(const uint8_t *data, size_t len);
int blk_is_valid(uint32_t block_num);
uint32_t blk_get_total_blocks(void);