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Read FRU data 255 bytes at a time, halving the count when the controller refuses it - #199
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bertysentry merged 2 commits intoOct 19, 2026
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…ler refuses it Read FRU Data asked for 16 bytes per round trip, so a 2 KB FRU cost 128 round trips. The first read of a controller now asks for 255 bytes and a refusal (C7h to CAh) halves the count down to 16, the way ipmitool backs off; the count a controller accepts serves its other FRUs. The offset advances by the bytes each reply returns, so the truncation offset in problems() is exact and a controller that returns no data within the size it declared is reported instead of being asked again. ReadFruData accepts a reply with a count of 0 and refuses one shorter than its count instead of failing on the array copy. Live (frus() with the SDR already walked): Lenovo IMM 15.0 s to 1.4 s, Lenovo XCC 8.3 s to 1.6 s, iLO 5 49.8 s to 26.8 s, Supermicro 0.27 s to 0.08 s, same FRUs and records. Supermicro, IMM, GIGABYTE, Fujitsu iRMC and iDRAC 6 answer 255; iLO 5 refuses it with C8h and answers 240; XCC and Dell F200 refuse it with C9h; iDRAC 8, Cisco IMC and F200 answer CAh to anything above 16 and read as before. Closes #102 Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
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…from the count sent A word-addressed FRU device takes its offset in words, so a 255-byte read left the next offset odd and the next read started one byte early. The count is kept even for such a device, but for the last read. The back-off starts from the count actually sent rather than from the chunk size, so a short FRU that is refused is asked again with a smaller count, and a refused tail of 16 bytes or less is a failure rather than a reason to shrink the reads of the next FRUs. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
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102-fru-reads-are-slow-read-fru-data-is-issued-in-16-byte-chunks
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October 19, 2026 17:54
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Closes #102.
FruReaderasked Read FRU Data for 16 bytes per round trip. The first read of a controller now asks for 255 bytes, and a refusal (C7htoCAh) halves the count down to 16, as ipmitool backs off; the count a controller accepts serves its other FRUs. The offset advances by the bytes each reply returns: the truncation offset inproblems()is exact, and a controller that returns no data within the size it declared is reported (No data returned).ReadFruDataaccepts a reply with a count of 0 and refuses one shorter than its count instead of failing on the array copy.Live probe of Read FRU Data counts (FRU 0, offset 0, one card per vendor): Supermicro, Lenovo IMM, GIGABYTE, Fujitsu iRMC, Dell iDRAC 6 and NetApp HCI answer 255; iLO 5 refuses 255 with
C8hand answers 240; Lenovo XCC and Dell F200 refuse 255 withC9h; iDRAC 8, both Cisco IMCs and the F200 answerCAhto anything above 16.Live
frus(), main vs this branch, SDR already walked, same FRUs and records on both:Unit tests on the fake BMC: a BMC refusing above 32 bytes is read in 32-byte chunks after three refusals, once for both of its FRUs; a refusal at 16 is reported as the FRU's problem; a reply shorter than asked advances by its bytes and an empty one ends the read. Docs:
fru-inventory.mddescribes the read,troubleshooting.mddrops the issue mention,upgrading.mdlists the change.🤖 Generated with Claude Code