Prevent unconnected ports from reporting oper status up

[sreeiyer-1]

Lucius creates fallback tap interfaces for ports whose kernel interfaces are absent. A later admin up is received for these interfaces can enable the tap interfaces and cause them to report The operational status as up. This can happen either at boot time or when the Ethernet interfaces is flapped.

Before processing the admin up request, check whether the eth interface derived from the first lane exists. If it is not present, ignore the admin request and leave the fallback port down. No change in the behaviour for connected ports and admin down requests.

In the test below, the topology used that 32 Ethernet interfaces with a breakout of 4. Only eth1 to eth16 are connected to a peer.

Ethernet48 below is an unconnected interface. The operational status follows admin status and shows as up :

root@sonic:/home/admin# show int status Ethernet48
  Interface        Lanes    Speed    MTU    FEC          Alias    Vlan    Oper    Admin                           Type    Asym PFC
-----------  -----------  -------  -----  -----  -------------  ------  ------  -------  -----------------------------  ----------
 Ethernet48  49,50,51,52      40G   9100    N/A  fortyGigE0/48  routed      up       up  OSFP 8X Pluggable Transceiver         N/A

root@sonic:/home/admin# config interface shut Ethernet48

root@sonic:/home/admin# show int status Ethernet48
  Interface        Lanes    Speed    MTU    FEC          Alias    Vlan    Oper    Admin                           Type    Asym PFC
-----------  -----------  -------  -----  -----  -------------  ------  ------  -------  -----------------------------  ----------
 Ethernet48  49,50,51,52      40G   9100    N/A  fortyGigE0/48  routed    down     down  OSFP 8X Pluggable Transceiver         N/A

root@sonic:/home/admin# config interface start Ethernet48
root@sonic:/home/admin# 
root@sonic:/home/admin# show int status Ethernet48
  Interface        Lanes    Speed    MTU    FEC          Alias    Vlan    Oper    Admin                           Type    Asym PFC
-----------  -----------  -------  -----  -----  -------------  ------  ------  -------  -----------------------------  ----------
 Ethernet48  49,50,51,52      40G   9100    N/A  fortyGigE0/48  routed      up       up  OSFP 8X Pluggable Transceiver         N/A

root@sonic:/home/admin# config interface start Ethernet48
root@sonic:/home/admin# sonic-db-cli APPL_DB HGETALL "PORT_TABLE:Ethernet48"
{'admin_status': 'up', 'alias': 'fortyGigE0/48', 'index': '13', 'lanes': '49,50,51,52', 'mtu': '9100', 'presence': '1', 'speed': '40000', 'id': '13', 'description': '', 'oper_status': 'up', 'flap_count': '3', 'last_up_time': 'Wed Sep 23 06:03:50 2026', 'last_down_time': 'Wed Sep 23 06:03:34 2026'}

After the changes :

root@sonic:/home/admin# show interfaces  status Ethernet48
  Interface        Lanes    Speed    MTU    FEC          Alias    Vlan    Oper    Admin                           Type    Asym PFC
-----------  -----------  -------  -----  -----  -------------  ------  ------  -------  -----------------------------  ----------
 Ethernet48  49,50,51,52      40G   9100    N/A  fortyGigE0/48  routed    down       up  OSFP 8X Pluggable Transceiver         N/A

root@sonic:/home/admin# config interface shut Ethernet48
root@sonic:/home/admin# show interfaces  status Ethernet48
  Interface        Lanes    Speed    MTU    FEC          Alias    Vlan    Oper    Admin                           Type    Asym PFC
-----------  -----------  -------  -----  -----  -------------  ------  ------  -------  -----------------------------  ----------
 Ethernet48  49,50,51,52      40G   9100    N/A  fortyGigE0/48  routed    down     down  OSFP 8X Pluggable Transceiver         N/A
root@sonic:/home/admin# 
root@sonic:/home/admin# config interface start Ethernet48
root@sonic:/home/admin# 
root@sonic:/home/admin# show interfaces  status Ethernet48
  Interface        Lanes    Speed    MTU    FEC          Alias    Vlan    Oper    Admin                           Type    Asym PFC
-----------  -----------  -------  -----  -----  -------------  ------  ------  -------  -----------------------------  ----------
 Ethernet48  49,50,51,52      40G   9100    N/A  fortyGigE0/48  routed    down       up  OSFP 8X Pluggable Transceiver         N/A

root@sonic:/home/admin# sonic-db-cli APPL_DB HGETALL "PORT_TABLE:Ethernet48"
{'admin_status': 'up', 'alias': 'fortyGigE0/48', 'index': '13', 'lanes': '49,50,51,52', 'mtu': '9100', 'presence': '1', 'speed': '40000', 'id': '13', 'description': '', 'oper_status': 'down', 'flap_count': '0'}

root@sonic:/var/log/swss# config interface start Ethernet48

2026/09/23 10:19:48 INFO ignoring admin-state update for port without backing interface oid=408 device=eth49 admin_state=true


root@sonic:/var/log/swss# config interface mtu Ethernet48 3000

2026/09/23 10:20:25 INFO setting port mtu oid=408 dev=eth49 mtu=3022
2026/09/23 10:20:25 ERROR failed to get link dev=eth49 err="Link not found"
2026/09/23 10:20:25 ERROR finished call protocol=grpc grpc.component=server grpc.service=lemming.dataplane.sai.Port grpc.method=SetPortAttribute grpc.method_type=unary peer.address=127.0.0.1:39710 grpc.start_time=2026-09-23T10:20:25Z grpc.code=Unknown grpc.error="Link not found" grpc.time_ms=0.323

Unit test

lemming/lemming$ go test ./dataplane/saiserver \
  -run 'TestSetPortAttribute/admin_status_ignored_without_backing_interface' \
  -v
go: downloading google.golang.org/genproto/googleapis/rpc v0.0.0-20260825221802-da73d73af1c5
go: downloading go.opentelemetry.io/otel v1.46.0
go: downloading go.opentelemetry.io/otel/trace v1.46.0
go: downloading github.com/go-logr/logr v1.4.4
go: downloading go.opentelemetry.io/otel/metric v1.46.0
=== RUN   TestSetPortAttribute
=== RUN   TestSetPortAttribute/admin_status_ignored_without_backing_interface
2026/09/23 10:32:23 INFO ignoring admin-state update for port without backing interface oid=3 device=eth125 admin_state=true
--- PASS: TestSetPortAttribute (0.01s)
    --- PASS: TestSetPortAttribute/admin_status_ignored_without_backing_interface (0.01s)
PASS
ok  	github.com/openconfig/lemming/dataplane/saiserver	0.048s

No change in the results of the other unit tests - GetSwitchStats continues to fail and all the other tests pass.

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[sonikajindal]

/gcbrun