bgpd: Move link_bw from attr_extra to bgp_path_info_extra

[ton31337]

No description provided.

[greptile-apps]

Greptile Summary

This PR removes the cached link_bw field from attr_extra and the associated bgp_attr_get_link_bw/bgp_attr_set_link_bw helpers, replacing eager extraction at attribute-parse time with an on-demand bgp_path_info_get_link_bw function that reads directly from the path's extended communities. It also fixes a latent side-effect bug in bgp_zebra_announce_parse_nexthop where the shared mpinfo->attr was being mutated mid-loop.

• bgp_attr.c / bgp_attr.h: Removes link_bw from attr_extra, the get/set inline helpers, and the bgp_attr_set_link_bw(attr, 0) cleanup calls in bgp_attr_unintern_sub and bgp_attr_flush.
• bgp_route.c / bgp_route.h: Adds bgp_path_info_get_link_bw, which calls ecommunity_linkbw_present on demand (standard then IPv6 ecommunity fallback).
• bgp_zebra.c: Rewires bgp_zebra_use_nhop_weighted to accept struct bgp_path_info * directly, eliminating the per-nexthop attr mutation in the announce loop.

Confidence Score: 4/5

Safe to merge; the refactoring correctly removes attr mutation side-effects and functional behaviour is preserved.

The change fixes a latent attr-mutation bug in the zebra announce loop, but introduces per-nexthop ecommunity scanning in place of a cached O(1) read, and misses a consolidation opportunity in bgp_mpath.c.

bgpd/bgp_route.c and its per-nexthop call site in bgpd/bgp_zebra.c deserve a second look for scale implications.

Important Files Changed

Filename	Overview
bgpd/bgp_attr.h	Removes link_bw field from attr_extra and the bgp_attr_get_link_bw/bgp_attr_set_link_bw inline helpers; cleans up refcount management logic tied to this cached field.
bgpd/bgp_attr.c	Drops the eager ecommunity_linkbw_present extraction in both bgp_attr_ext_communities and bgp_attr_ipv6_ext_communities, and removes the bgp_attr_set_link_bw(attr, 0) cleanup calls from bgp_attr_unintern_sub and bgp_attr_flush.
bgpd/bgp_route.c	Introduces bgp_path_info_get_link_bw, which computes link bandwidth on demand by calling ecommunity_linkbw_present rather than reading a cached value; called in the per-nexthop announce loop.
bgpd/bgp_route.h	Exports the new bgp_path_info_get_link_bw declaration.
bgpd/bgp_zebra.c	Updates bgp_zebra_use_nhop_weighted to accept struct bgp_path_info * instead of struct attr *, and removes the inline extraction + mutation of mpinfo->attr's link_bw in the announce loop.

Sequence Diagram

sequenceDiagram
    participant Parser as bgp_attr_ext_communities (parse time)
    participant Announce as bgp_zebra_announce_parse_nexthop
    participant WeightFn as bgp_zebra_use_nhop_weighted
    participant LinkBW as bgp_path_info_get_link_bw (NEW)
    participant ECom as ecommunity_linkbw_present

    note over Parser: BEFORE (removed): link_bw extracted once and cached in attr_extra
    Parser->>ECom: "ecommunity_linkbw_present(ecom, &link_bw)"
    Parser->>Parser: bgp_attr_set_link_bw(attr, link_bw)

    note over Announce: BEFORE: O(1) cached lookup
    Announce->>WeightFn: "bgp_zebra_use_nhop_weighted(bgp, attr, &weight)"
    WeightFn->>WeightFn: bgp_attr_get_link_bw(attr) - read cached value

    note over Announce: AFTER (new): on-demand parse per nexthop
    loop for each mpinfo
        Announce->>WeightFn: "bgp_zebra_use_nhop_weighted(bgp, mpinfo, &weight)"
        WeightFn->>LinkBW: bgp_path_info_get_link_bw(bpi)
        LinkBW->>ECom: "ecommunity_linkbw_present(ecommunity, &link_bw)"
        alt link_bw not found
            LinkBW->>ECom: "ecommunity_linkbw_present(ipv6_ecommunity, &link_bw)"
        end
        LinkBW-->>WeightFn: link_bw
    end

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Prompt To Fix All With AI

Fix the following 2 code review issues. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 2
bgpd/bgp_route.c:440-452
**On-demand parsing called per nexthop in a hot loop**

`bgp_path_info_get_link_bw` is called once per multipath nexthop in `bgp_zebra_announce_parse_nexthop` (inside the `for (; mpinfo; ...)` loop). Previously the value was extracted once during attribute parsing and cached in `attr_extra->link_bw` for O(1) lookup. Now it calls `ecommunity_linkbw_present`, which linearly scans all ecommunity entries, on every nexthop iteration. For large multipath groups over link-BW ECMP this will scan the ecommunity list O(nexthops) times rather than once at parse time. The impact is bounded by typically small ecommunity list sizes, but it is a measurable regression on the critical path of route installation.

### Issue 2 of 2
bgpd/bgp_route.c:436-452
**Duplicate two-step ecommunity check pattern in `bgp_mpath.c` not consolidated**

`bgp_mpath.c` lines 554–558 contain the same identical two-step `ecommunity_linkbw_present` fallback pattern (`ecommunity` → `ipv6_ecommunity`) that this new helper encapsulates. If the intent is to centralise link-bandwidth extraction through `bgp_path_info_get_link_bw`, the `bgp_mpath.c` site is an obvious candidate for the same treatment.

_{Reviews (1): Last reviewed commit: "bgpd: Move link_bw from attr_extra to bg..." | Re-trigger Greptile}