[LU-19991] FLR-EC-IWM: llapi layout support and kernel layout passthrough for immediate mirrors

• Type: Technical task
• Resolution: Unresolved
• Priority: Medium
• Labels: FLR-EC FLR-EC-IWM
• Severity: 3
• Assignee: WC Triage
• Reporter: Patrick Farrell

Description

Add llapi validation and kernel layout support for LCME_FL_IMMEDIATE, following the EC pattern (Gerrit 61962, commit 77982cf6b6).

llapi (liblustreapi_layout.c, lustreapi.h):

• Layout validation for immediate mirror components
• Mutual exclusion: LCME_FL_IMMEDIATE and LCME_FL_PARITY cannot coexist on the same component
• Validation that immediate mirrors have >= 2 mirrors

Kernel layout passthrough:

• LOD (lod_lov.c, lod_object.c): verify LCME_FL_IMMEDIATE flows through lod_parse_striping/lod_generate_lovea and default layout propagation via LCME_TEMPLATE_FLAGS
• LOV (lov_ea.c, lov_internal.h): add lsme_is_immediate() and lre_immediate helpers, verify flag flows through composite layout init
• Wire format (pack_generic.c): verify no new fields needed

Tests (llapi_layout_test.c):

• Create layout with LCME_FL_IMMEDIATE via llapi
• Verify flag round-trips through get/set
• Verify IMMEDIATE + PARITY mutual exclusion
• Verify rejection with < 2 mirrors
• Verify kernel stores and returns the flag

Reference EC patches:

• Gerrit 61962 (commit 77982cf6b6): LU-12187 llapi: EC layout creation support (pattern – 14 files, 1856 lines)

Note: IWM version will be much smaller than EC – EC needed RAID set math, stripe count derivation, and parity binding. IWM just needs flag validation and passthrough.

Issue Links

• is blocked by: LU-19989 FLR-EC-IWM: connect flag, feature gating, and LCME_FL_IMMEDIATE flag
• is blocking: LU-19993 FLR-EC-IWM: lfs setstripe --immediate support