ipmi-lite: Fix IPMI SEL rollover (Record ID 0 collision with SEL_RECID_FIRST)

[louis-nexthop]

Description

Fixes #273

Context

IPMI Specification: https://www.intel.la/content/dam/www/public/us/en/documents/specification-updates/ipmi-intelligent-platform-mgt-interface-spec-2nd-gen-v2-0-spec-update.pdf

The standard IPMI SEL "iterator" protocol

An IPMI client (e.g. ipmitool sel list) walks the log by:

1. Issuing Get SEL Entry with read_rec_id = 0x0000 (SEL_RECID_FIRST).
2. Receiving the entry plus a next_rec_id.
3. Re-issuing Get SEL Entry with read_rec_id = next_rec_id.
4. Stopping when the returned next_rec_id == 0xFFFF (SEL_RECID_LAST).

What was done

Fix index and record ID calculations in sel_get_entry() and sel_add_entry(), so they are consistent with these conventions from the specs:

• index is 0-indexed.
• record ID is 1-indexed.
  • record ID = 0x0000 (SEL_RECID_FIRST) is reserved with a special meaning for access command (GET FIRST ENTRY; "give me the first record")
  • record ID = 0xFFFF (SEL_RECID_LAST) is reserved with a special meaning for access command (GET LAST ENTRY; "give me the last record")
• g_sel_hdr[node].begin is the first index of the buffer
• g_sel_hdr[node].end is the next empty slot of the buffer

Motivation

The rollover logic had a flaw.

sel.c used Record ID 0x0000 which should be reserved.

After ring-buffer rollover, ipmitool's Get SEL Entry chain hit a *next_rec_id = 0 (post-wrap), re-issued Get SEL Entry(0), and sel_get_entry() returned the first record again — infinite loop, broken by ipmitool's cycle-detection. Symptom: host's ipmitool sel list collapsed to a single row after rollover.

Test Plan

Before:

# Initial: have 129 SEL records
[root@fboss ~]# ipmitool sel list | wc -l
129

# Bug: ID "1" is duplicated
[root@fboss ~]# ipmitool sel list | head -4
   1 | 05/14/2026 | 20:40:26 | Processor #0x40 | Uncorrectable machine check exception | Asserted
   1 | 05/14/2026 | 20:40:26 | Processor #0x40 | Uncorrectable machine check exception | Asserted
   2 | 05/14/2026 | 20:42:44 | Processor #0x40 | Uncorrectable machine check exception | Asserted
   3 | 05/14/2026 | 20:45:02 | Processor #0x40 | Uncorrectable machine check exception | Asserted
[root@fboss ~]# ipmitool sel list | tail -3
  7e | 05/28/2026 | 05:01:09 | Temperature #0x17 |  | Asserted
  7f | 05/28/2026 | 05:03:36 | Temperature #0x17 |  | Asserted
  80 | 05/28/2026 | 05:03:50 | Temperature #0x17 |  | Asserted

# Then: add 1 more record
[root@fboss ~]# ipmitool raw 0x0a 0x44 0x01 0x00 0x02 0xab 0xcd 0xef 0x00 0x01 0x00 0x04 0x01 0x17 0x00 0xa0 0x04 0x07
 00 00

# Bug: new entry is not shown. It only output the record with ID "2" which was existing
[root@fboss ~]# ipmitool sel list | wc -l
1
[root@fboss ~]# ipmitool sel list
   2 | 05/14/2026 | 20:42:44 | Processor #0x40 | Uncorrectable machine check exception | Asserted

After (flash BMC with a new image):

# Correctly report maximum of 128 SEL records
[root@fboss ~]# ipmitool sel list | wc -l
128

# The order is correct (although, the incorrect record ID "0" is still shown from the previous image)
[root@fboss ~]# ipmitool sel list | head -3
   2 | 05/14/2026 | 20:42:44 | Processor #0x40 | Uncorrectable machine check exception | Asserted
   3 | 05/14/2026 | 20:45:02 | Processor #0x40 | Uncorrectable machine check exception | Asserted
   4 | 05/14/2026 | 20:47:20 | Processor #0x40 | Uncorrectable machine check exception | Asserted
[root@fboss ~]# ipmitool sel list | tail -3
  7f | 05/28/2026 | 05:03:36 | Temperature #0x17 |  | Asserted
  80 | 05/28/2026 | 05:03:50 | Temperature #0x17 |  | Asserted
   0 | 05/28/2026 | 05:05:29 | Temperature #0x17 |  | Asserted

# Try to inject 129 more entries to overflow again
[root@fboss ~]# for i in {1..129}; do \
    ipmitool raw 0x0a 0x44 0x01 0x00 0x02 0xab 0xcd 0xef 0x00 0x01 0x00 0x04 0x01 0x17 0x00 0xa0 0x04 0x07; \
    sleep 0.5s; \
    done;

# Report correct number of entries (128 max)
[root@fboss ~]# ipmitool sel list | wc -l
128

# Order looks correct (it's expected that Record ID 2 is evicted; array has 129 slots but 128 entries max)
[root@fboss ~]# ipmitool sel list | head -2
   3 | 05/28/2026 | 05:48:15 | Temperature #0x17 |  | Asserted
   4 | 05/28/2026 | 05:48:16 | Temperature #0x17 |  | Asserted
[root@fboss ~]# ipmitool sel list | tail -2
  81 | 05/28/2026 | 05:49:21 | Temperature #0x17 |  | Asserted
   1 | 05/28/2026 | 05:50:30 | Temperature #0x17 |  | Asserted

[meta-codesync]

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