[M] Change in ...osmo-s1gw[master]: erab_fsm: implement E-RAB MODIFY Req/Rsp procedures - gerrit-log

10 Dec 2024

fixeria has uploaded this change for review. ( https://gerrit.osmocom.org/c/erlang/osmo-s1gw/+/39116?usp=email )
Change subject: erab_fsm: implement E-RAB MODIFY Req/Rsp procedures
......................................................................
erab_fsm: implement E-RAB MODIFY Req/Rsp procedures
Change-Id: I24d57ea390d71b640cb42046a8658e9d30670682
---
M src/erab_fsm.erl
M test/erab_fsm_test.erl
M test/pfcp_mock.hrl
3 files changed, 162 insertions(+), 24 deletions(-)
git pull ssh://gerrit.osmocom.org:29418/erlang/osmo-s1gw refs/changes/16/39116/1

diff --git a/src/erab_fsm.erl b/src/erab_fsm.erl
index a479cea..35df15f 100644
--- a/src/erab_fsm.erl
+++ b/src/erab_fsm.erl
@@ -49,6 +49,8 @@
 -export([start_link/1,
          erab_setup_req/2,
          erab_setup_rsp/2,
+         erab_modify_req/2,
+         erab_modify_rsp/2,
          erab_release/2,
          erab_release_cmd/1,
          erab_release_rsp/1,
@@ -73,6 +75,9 @@
                       addr()  %% GTP-U Transport Layer Address
                      }.
+-type mod_kind() :: setup_rsp |
+                    modify_req |
+                    modify_rsp_nack.
 -type rel_kind() :: cmd | ind.
-record(erab_state, {uid :: term(), %% unique E-RAB identifier
@@ -81,8 +86,10 @@
                      c2u :: undefined | teid_addr(), %% GTP-U params for UPF <- Core
                      a2u :: undefined | teid_addr(), %% GTP-U params for UPF <- Access
                      u2a :: undefined | teid_addr(), %% GTP-U params for UPF -> Access
+                     u2cm :: undefined | teid_addr(), %% GTP-U params for UPF -> Core (modified)
                      seid_loc :: undefined | pfcp_peer:pfcp_seid(), %% local SEID, chosen by us
                      seid_rem :: undefined | pfcp_peer:pfcp_seid(), %% remote SEID, chosen by the UPF
+                     mod_kind :: undefined | mod_kind(), %% E-RAB MODIFY kind
                      rel_kind :: undefined | rel_kind() %% E-RAB RELEASE kind
                     }).
@@ -127,6 +134,28 @@
     gen_statem:call(Pid, {?FUNCTION_NAME, F_TEID}).
+%% @doc Indicate reception of E-RAB modify request (from core).
+%% @param Pid  PID of an erab_fsm.
+%% @param F_TEID  TEID and bind address indicated by the MME.
+%% @returns TEID and Addr to be sent to the eNB;  an error otherwise.
+%% @end
+-spec erab_modify_req(pid(), teid_addr()) -> {ok, teid_addr()} |
+                                             {error, term()}.
+erab_modify_req(Pid, F_TEID) ->
+    gen_statem:call(Pid, {?FUNCTION_NAME, F_TEID}).
+
+
+%% @doc Indicate reception of E-RAB modify response (from access).
+%% @param Pid  PID of an erab_fsm.
+%% @param Res  ack  if eNB indicates successful modification;
+%%             nack if eNB indicates unsuccessful modification.
+%% @returns ok or an error.
+%% @end
+-spec erab_modify_rsp(pid(), ack | nack) -> ok | {error, term()}.
+erab_modify_rsp(Pid, Res) ->
+    gen_statem:call(Pid, {?FUNCTION_NAME, Res}).
+
+
 -spec erab_release(pid(), rel_kind()) -> ok.
 erab_release(Pid, cmd) ->
     erab_release_cmd(Pid);
@@ -256,7 +285,8 @@
                     #erab_state{} = S) ->
     ?LOG_DEBUG("Rx E-RAB SETUP Rsp (U2A ~p)", [U2A]),
     {next_state, session_modify,
-     S#erab_state{from = From,
+     S#erab_state{mod_kind = setup_rsp,
+                  from = From,
                   u2a = U2A}};
erab_wait_setup_rsp(Event, EventData, S) ->
@@ -264,7 +294,8 @@
%% state SESSION_MODIFY :: PFCP session modification
-session_modify(enter, OldState, S) ->
+session_modify(enter, OldState,
+               #erab_state{} = S) ->
     ?LOG_DEBUG("State change: ~p -> ~p", [OldState, ?FUNCTION_NAME]),
     ok = session_modify_req(S),
     {next_state, ?FUNCTION_NAME, S, %% loop transition to enable state_timeout
@@ -277,24 +308,32 @@
      {shutdown, timeout},
      {reply, From, {error, {timeout, ?FUNCTION_NAME}}}};
-session_modify(info, #pfcp{} = PDU,
+session_modify(info, #pfcp{type = session_modification_response,
+                           seid = SEID_Rsp, %% matches F-SEID we sent in the ESTABLISH Req
+                           ie = #{pfcp_cause := 'Request accepted'}},
                #erab_state{from = From,
                            seid_loc = SEID_Rsp,
-                           c2u = C2U} = S) ->
-    case PDU of
-        #pfcp{type = session_modification_response,
-              seid = SEID_Rsp, %% matches F-SEID we sent in the ESTABLISH Req
-              ie = #{pfcp_cause := 'Request accepted'}} ->
-            ?LOG_DEBUG("PFCP session modified"),
-            {next_state, erab_setup,
-             S#erab_state{from = undefined},
-             [{reply, From, {ok, C2U}}]};
-        _ ->
-            ?LOG_ERROR("Rx unexpected PFCP PDU: ~p", [PDU]),
-            {stop_and_reply,
-             {shutdown, unexp_pdu},
-             {reply, From, {error, {unexp_pdu, ?FUNCTION_NAME}}}}
-    end;
+                           mod_kind = ModKind} = S) ->
+    ?LOG_DEBUG("PFCP session modified"),
+    Reply = case ModKind of
+        setup_rsp ->
+            {ok, S#erab_state.c2u};
+        modify_req ->
+            {ok, S#erab_state.a2u};
+        modify_rsp_nack ->
+            ok
+    end,
+    {next_state, erab_setup,
+     S#erab_state{mod_kind = undefined,
+                  from = undefined},
+     [{reply, From, Reply}]};
+
+session_modify(info, #pfcp{} = PDU,
+               #erab_state{from = From}) ->
+    ?LOG_ERROR("Rx unexpected PFCP PDU: ~p", [PDU]),
+    {stop_and_reply,
+     {shutdown, unexp_pdu},
+     {reply, From, {error, {unexp_pdu, ?FUNCTION_NAME}}}};
session_modify(Event, EventData, S) ->
     handle_event(?FUNCTION_NAME, Event, EventData, S).
@@ -306,6 +345,33 @@
     {keep_state, S};
erab_setup({call, From},
+           {erab_modify_req, U2CM},
+           #erab_state{} = S) ->
+    ?LOG_DEBUG("Rx E-RAB MODIFY Req (U2CM ~p)", [U2CM]),
+    {next_state, session_modify,
+     S#erab_state{mod_kind = modify_req,
+                  from = From,
+                  u2cm = U2CM}};
+
+erab_setup({call, From},
+           {erab_modify_rsp, Res},
+           #erab_state{u2cm = U2CM} = S0) ->
+    ?LOG_DEBUG("Rx E-RAB MODIFY Rsp (~p)", [Res]),
+    case Res of
+        ack ->
+            {keep_state,
+             S0#erab_state{u2c = U2CM,
+                           u2cm = undefined},
+             {reply, From, ok}};
+        nack ->
+            %% revert PFCP session params
+            {next_state, session_modify,
+             S0#erab_state{mod_kind = modify_rsp_nack,
+                           u2cm = undefined,
+                           from = From}}
+    end;
+
+erab_setup({call, From},
            erab_release_cmd,
            #erab_state{} = S) ->
     ?LOG_DEBUG("Rx E-RAB RELEASE Cmd"),
@@ -466,19 +532,49 @@
-spec session_modify_req(erab_state()) -> pfcp_peer:pfcp_session_rsp().
-session_modify_req(#erab_state{seid_rem = SEID, %% SEID allocated to us
+session_modify_req(#erab_state{mod_kind = setup_rsp,
+                               seid_rem = SEID,
                                u2a = U2A}) ->
+    %% Now we know the Access side TEID / GTP-U address, so we modify
+    %% the FAR1 (which was previously set to DROP) to FORW.
+    session_modify_req(SEID, 1, U2A);
+
+session_modify_req(#erab_state{mod_kind = modify_req,
+                               seid_rem = SEID,
+                               u2cm = U2CM}) ->
+    %% E-RAB MODIFY Req - MME orders modification of U2C F-TEID,
+    %% so we modify the respective FAR (id=2)
+    session_modify_req(SEID, 2, U2CM);
+
+session_modify_req(#erab_state{mod_kind = modify_rsp_nack,
+                               seid_rem = SEID,
+                               u2c = U2C}) ->
+    %% E-RAB MODIFY Rsp (NACK) - eNB NACK's E-RAB modification
+    %% so we modify the respective FAR (id=2)
+    session_modify_req(SEID, 2, U2C).
+
+
+-spec session_modify_req(SEID, FAR_ID, F_TEID) -> Result
+    when SEID :: pfcp_peer:pfcp_seid(),
+         FAR_ID :: integer(),
+         F_TEID :: teid_addr(),
+         Result :: pfcp_peer:pfcp_session_rsp().
+session_modify_req(SEID, FAR_ID, F_TEID) ->
     %% Forwarding Action Rules
-    FPars = #{outer_header_creation => ohc(U2A)},
-    FParsNI = add_net_inst(FPars, 'Access'), %% optional Network Instance IE
-    FARs = [#{far_id => {far_id, 1}, %% -- for Core -> Access
-              %% Now we know the Access side TEID / GTP-U address, so we modify
-              %% this FAR (which was previously set to DROP) to FORW.
+    Iface = far_id2iface(FAR_ID),
+    FPars = #{outer_header_creation => ohc(F_TEID)},
+    FParsNI = add_net_inst(FPars, Iface), %% optional Network Instance IE
+    FARs = [#{far_id => {far_id, FAR_ID},
               apply_action => #{'FORW' => []},
               update_forwarding_parameters => FParsNI}],
     pfcp_peer:session_modify_req(SEID, [], FARs).
+-spec far_id2iface(integer()) -> iface().
+far_id2iface(1) -> 'Access';
+far_id2iface(2) -> 'Core'.
+
+
 %% Network Instance IE env parameter name
 -spec net_inst_param(iface()) -> atom().
 net_inst_param('Core') -> pfcp_net_inst_core;
diff --git a/test/erab_fsm_test.erl b/test/erab_fsm_test.erl
index e406e88..5563d02 100644
--- a/test/erab_fsm_test.erl
+++ b/test/erab_fsm_test.erl
@@ -8,6 +8,8 @@
 -define(A2U, {?TEID_A2U, ?ADDR_A2U}).
 -define(U2A, {?TEID_U2A, ?ADDR_U2A}).
+-define(U2CM, {?TEID_U2CM, ?ADDR_U2CM}).
+
 %% ------------------------------------------------------------------
 %% setup/misc functions
 %% ------------------------------------------------------------------
@@ -48,6 +50,13 @@
       ?TC(fun test_erab_setup_pfcp_modify_error/1)}].
+erab_modify_test_() ->
+    [{"E-RAB MODIFY REQ :: ACK",
+      ?TC(fun test_erab_modify_req_ack/1)},
+     {"E-RAB MODIFY REQ :: NACK",
+      ?TC(fun test_erab_modify_req_nack/1)}].
+
+
 erab_release_test_() ->
     [{"E-RAB RELEASE CMD :: success",
       ?TC(fun test_erab_release_cmd_success/1)},
@@ -105,6 +114,35 @@
      ?_assertNot(erlang:is_process_alive(Pid))].
+test_erab_modify_req(Pid, Res) ->
+    U2C = case Res of
+        ack -> ?U2CM;
+        nack -> ?U2C
+    end,
+    [?_assertEqual({ok, ?A2U}, erab_fsm:erab_setup_req(Pid, ?U2C)),
+     ?_assertEqual({ok, ?C2U}, erab_fsm:erab_setup_rsp(Pid, ?U2A)),
+     %% E-RAB MODIFY Req indicates the new (modified) F-TEID to be used
+     %% in the UPF -> Core direction.  The FSM logic indicates the old
+     %% (unmodified) F-TEID to be used in the UPF <- Access direction.
+     ?_assertEqual({ok, ?A2U}, erab_fsm:erab_modify_req(Pid, ?U2CM)),
+     %% Before getting the Rsp, the U2C F-TEID remains unchanged
+     ?_assertEqual(?U2C, erab_fsm_info(Pid, f_teid_u2c)),
+     %% After getting the Rsp (ACK), the new (modified) U2C F-TEID is used
+     %% After getting the Rsp (NACK), the U2C F-TEID remains unchanged
+     ?_assertEqual(ok, erab_fsm:erab_modify_rsp(Pid, Res)),
+     ?_assertEqual(U2C, erab_fsm_info(Pid, f_teid_u2c)),
+     ?_assertEqual(ok, erab_fsm:shutdown(Pid)),
+     ?_assertNot(erlang:is_process_alive(Pid))].
+
+
+test_erab_modify_req_ack(Pid) ->
+    test_erab_modify_req(Pid, ack).
+
+
+test_erab_modify_req_nack(Pid) ->
+    test_erab_modify_req(Pid, nack).
+
+
 test_erab_release_cmd_success(Pid) ->
     [?_assertEqual({ok, ?A2U}, erab_fsm:erab_setup_req(Pid, ?U2C)),
      ?_assertEqual({ok, ?C2U}, erab_fsm:erab_setup_rsp(Pid, ?U2A)),
diff --git a/test/pfcp_mock.hrl b/test/pfcp_mock.hrl
index c044939..9a0232a 100644
--- a/test/pfcp_mock.hrl
+++ b/test/pfcp_mock.hrl
@@ -6,9 +6,13 @@
 -define(TEID_A2U,   16#0202). %% UPF <- Access
 -define(TEID_U2A,   16#0002). %% UPF -> Access
+-define(TEID_U2CM,  16#0f0001). %% UPF -> Core (modified)
+
 -define(ADDR_U2C,   << 16#7f, 16#00, 16#00, 16#01 >>). %% UPF -> Core
 -define(ADDR_C2U,   << 16#7f, 16#00, 16#01, 16#01 >>). %% UPF <- Core
 -define(ADDR_A2U,   << 16#7f, 16#00, 16#02, 16#02 >>). %% UPF <- Access
 -define(ADDR_U2A,   << 16#7f, 16#00, 16#00, 16#02 >>). %% UPF -> Access
+-define(ADDR_U2CM,  << 16#7f, 16#0f, 16#00, 16#01 >>). %% UPF -> Core (modified)
+
 %% vim:set ts=4 sw=4 et:
-- 
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Gerrit-MessageType: newchange
Gerrit-Project: erlang/osmo-s1gw
Gerrit-Branch: master
Gerrit-Change-Id: I24d57ea390d71b640cb42046a8658e9d30670682
Gerrit-Change-Number: 39116
Gerrit-PatchSet: 1
Gerrit-Owner: fixeria vyanitskiy@sysmocom.de



    