bgpd: Fix BGP-LS initial TED sync and cleanup on peer deactivation

[cscarpitta]

This PR fixes two issues in the BGP-LS code.

Initial sync: After registering with the LS database, BGP-LS never requests a sync, leaving the TED empty until the IGP sends unsolicited updates. Fix by calling `ls_request_sync() after registration.

Peer deactivation: When the last BGP-LS peer is deactivated, self-originated routes are not withdrawn and the TED is not cleared, leaving stale state. Fix by adding bgp_ls_withdraw_ted() and calling it from peer_deactivate().

[greptile-apps]

Greptile Summary

This PR fixes two correctness gaps in the BGP-LS subsystem: the TED was never populated on startup because the initial sync was never requested, and stale self-originated routes plus TED state were left behind when the last BGP-LS peer was deactivated.

• Initial sync: ls_request_sync() is now called immediately after ls_register() in bgp_ls_register(). Failure is non-fatal (logged as a warning) and registration is still marked successful, which is the right trade-off.
• LS_MSG_EVENT_SYNC dispatch: LS_MSG_EVENT_SYNC was missing from all three per-object switch statements (bgp_ls_process_vertex, bgp_ls_process_edge, bgp_ls_process_subnet) and from the edge-level bidirectional-linking condition in bgp_ls_process_message. All four sites now treat SYNC identically to ADD, matching the intended semantics.
• Peer deactivation cleanup: New bgp_ls_ted_clear() (static) and bgp_ls_withdraw_ted() (exported) clean up the RIB and TED when the last peer goes away. bgp_clear_route(bgp->peer_self, AFI_BGP_LS, SAFI_BGP_LS) correctly targets only self-originated paths; bgp_ls_ted_clear uses frr_each_safe for safe in-place deletion. The call in bgpd.c happens before bgp_ls_unregister(), ensuring withdrawals are issued while the zebra subscription is still live.
• Test coverage: Two new topotests (test_bgp_ls_peer_deactivate / test_bgp_ls_peer_reactivate) exercise the full deactivate-then-reactivate cycle on both the producer (r2) and consumer (rr) routers.

Confidence Score: 4/5

• PR is safe to merge; both fixes are correct and well-targeted, with topotest coverage for the new behaviour.
• The logic is sound: ls_request_sync is placed correctly after registration, LS_MSG_EVENT_SYNC is now handled consistently across all dispatch sites, and bgp_ls_withdraw_ted correctly uses bgp_clear_route(peer_self, …) to hit only self-originated paths before clearing the TED. The one noteworthy design point — bgp_clear_route enqueues work asynchronously while bgp_ls_ted_clear runs synchronously — is functionally safe because the withdrawal work queue does not consult TED state. Score of 4 rather than 5 only because this is new non-trivial state-management code that benefits from a second pair of eyes before landing.
• bgpd/bgp_ls_ted.c — new bgp_ls_withdraw_ted function and SYNC dispatch additions are the most impactful changes and deserve careful review.

Important Files Changed

Filename	Overview
bgpd/bgp_ls.c	Adds ls_request_sync() call after successful ls_register() to trigger initial TED population; correctly continues even on sync failure with a warning log.
bgpd/bgp_ls_ted.c	Adds LS_MSG_EVENT_SYNC to all switch-case handlers (vertex/edge/subnet) and edge-level bidirectional linking logic; introduces bgp_ls_ted_clear() and bgp_ls_withdraw_ted() for bulk TED cleanup on peer deactivation. bgp_clear_route is async while bgp_ls_ted_clear is synchronous — functionally safe but worth noting.
bgpd/bgp_ls_ted.h	Exports the new bgp_ls_withdraw_ted() declaration with a clear docstring describing its contract.
bgpd/bgpd.c	Calls bgp_ls_withdraw_ted() before bgp_ls_unregister() in the last-peer deactivation path — correct ordering ensures routes are withdrawn before the zebra subscription is dropped.
tests/topotests/bgp_link_state/test_bgp_link_state.py	Adds check_bgp_ls_empty() helper and two new end-to-end tests: test_bgp_ls_peer_deactivate and test_bgp_ls_peer_reactivate, following existing file patterns.

Sequence Diagram

sequenceDiagram
    participant Peer as BGP-LS Peer
    participant bgpd as bgpd (peer_deactivate)
    participant LSTD as bgp_ls_withdraw_ted
    participant RIB as BGP RIB (async work queue)
    participant TED as ls_ted
    participant Zebra as Zebra LS DB

    Note over Peer,Zebra: --- Initial Registration ---
    Peer->>bgpd: activate (first peer)
    bgpd->>Zebra: ls_register()
    bgpd->>Zebra: ls_request_sync()
    Zebra-->>bgpd: LS_MSG_EVENT_SYNC messages
    bgpd->>TED: ls_vertex/edge/subnet add
    bgpd->>RIB: bgp_ls_originate_node/link/prefix

    Note over Peer,Zebra: --- Peer Deactivation (last peer) ---
    Peer->>bgpd: deactivate (last peer)
    bgpd->>LSTD: bgp_ls_withdraw_ted(bgp)
    LSTD->>RIB: bgp_clear_route(peer_self, AFI_BGP_LS, SAFI_BGP_LS)
    RIB-->>Peer: BGP UPDATE withdrawals (async)
    LSTD->>TED: bgp_ls_ted_clear() — remove all vertices/edges/subnets
    bgpd->>Zebra: bgp_ls_unregister()

    Note over Peer,Zebra: --- Re-activation ---
    Peer->>bgpd: activate (new peer)
    bgpd->>Zebra: ls_register()
    bgpd->>Zebra: ls_request_sync()
    Zebra-->>bgpd: LS_MSG_EVENT_SYNC messages
    bgpd->>TED: re-populate
    bgpd->>RIB: re-originate all NLRIs

Loading

_{Reviews (1): Last reviewed commit: "tests: Verify BGP-LS routes withdrawn on..." | Re-trigger Greptile}