mctpd: Improve sequencing of Set Endpoint ID responses in endpoint mode

CHANGELOG.md

@@ -38,6 +38,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
    re-use outgoing control protocol instance IDs (IIDs) when we re-send
    commands. More instances of commands now have retry logic too.
 
+3. When running in endpoint mode, `mctpd` will now issue responses to incoming
+   Set Endpoint ID commands before performing enumeration on the (bus-owner)
+   peer.
+
 ## [2.5] - 2026-02-17
 
 ### Added

src/mctpd.c

@@ -894,27 +894,44 @@ static int handle_control_set_endpoint_id(struct ctx *ctx, int sd,
 		if (rc < 0) {
 			warnx("ERR: cannot add local eid %d to ifindex %d",
 			      req->eid, addr->smctp_ifindex);
+			resp_len = sizeof(struct mctp_ctrl_resp);
 			resp->completion_code = MCTP_CTRL_CC_ERROR_NOT_READY;
+			reply_message(ctx, sd, resp, resp_len, addr);
+			return rc;
 		}
 
 		rc = add_peer_from_addr(ctx, addr, &peer);
-		if (rc == 0) {
-			rc = setup_added_peer(peer);
-		}
-		if (rc < 0) {
-			warnx("ERR: cannot add bus owner to object lists");
+		if (rc) {
+			errno = -rc;
+			warn("failed setting up bus owner, rejecting Set EID");
+			resp->completion_code = MCTP_CTRL_CC_ERROR;
+			resp_len = sizeof(struct mctp_ctrl_resp);
+			reply_message(ctx, sd, resp, resp_len, addr);
+			return rc;
 		}
 
-		if (link_data->discovered != DISCOVERY_UNSUPPORTED) {
+		add_peer_route(peer);
+
+		if (link_data->discovered != DISCOVERY_UNSUPPORTED)
 			link_data->discovered = DISCOVERY_DISCOVERED;
-		}
+
 		resp->status =
 			SET_MCTP_EID_ASSIGNMENT_STATUS(MCTP_SET_EID_ACCEPTED) |
 			SET_MCTP_EID_ALLOCATION_STATUS(MCTP_SET_EID_POOL_NONE);
 		resp->eid_set = req->eid;
 		resp->eid_pool_size = 0;
-		fprintf(stderr, "Accepted set eid %d\n", req->eid);
-		return reply_message(ctx, sd, resp, resp_len, addr);
+		rc = reply_message(ctx, sd, resp, resp_len, addr);
+		if (rc) {
+			errno = -rc;
+			warn("failed responding to set eid request");
+			return rc;
+		}
+
+		rc = setup_added_peer(peer);
+		if (rc < 0)
+			warnx("ERR: cannot add bus owner to object lists");
+
+		return 0;
 
 	case MCTP_SET_EID_DISCOVERED:
 		if (link_data->discovered == DISCOVERY_UNSUPPORTED) {
@@ -2591,6 +2608,8 @@ static int get_endpoint_peer(struct ctx *ctx, sd_bus_error *berr,
 		rc = add_peer(ctx, dest, eid, net, &peer, false);
 		if (rc < 0)
 			return rc;
+
+		add_peer_route(peer);
 	}
 
 	peer->endpoint_type = ep_type;
@@ -2970,6 +2989,7 @@ static int method_setup_endpoint(sd_bus_message *call, void *data,
 		} else if (rc < 0) {
 			goto err;
 		} else {
+			add_peer_route(peer);
 			peer->endpoint_type = ep_type;
 			peer->medium_spec = medium_spec;
 			rc = setup_added_peer(peer);
@@ -3296,11 +3316,6 @@ static int setup_added_peer(struct peer *peer)
 	// this with .SetMTU as needed
 	peer->mtu = mctp_nl_min_mtu_byindex(peer->ctx->nl, peer->phys.ifindex);
 
-	// add route before querying for non-bridged endpoints.
-	// bridged endpoints will use the bridge's pool range route.
-	if (!is_eid_in_bridge_pool(n, peer->ctx, peer->eid))
-		add_peer_route(peer);
-
 	rc = query_peer_properties(peer);
 	if (rc < 0)
 		goto out;

tests/test_mctpd.py

@@ -127,7 +127,7 @@ async def test_setup_endpoint(dbus, mctpd):
     assert neigh.eid == ep.eid
 
     # we should have a route for the new endpoint too
-    assert len(mctpd.system.routes) == 2
+    assert len(mctpd.system.routes) == 1
 
 
 async def test_setup_endpoint_conflict(dbus, mctpd):
@@ -356,7 +356,7 @@ async def test_assign_endpoint_static(dbus, mctpd):
     neigh = mctpd.system.neighbours[0]
     assert neigh.lladdr == dev.lladdr
     assert neigh.eid == static_eid
-    assert len(mctpd.system.routes) == 2
+    assert len(mctpd.system.routes) == 1
 
 
 async def test_assign_endpoint_static_allocated(dbus, mctpd):