[1/4] Adopt iu_client from osmo-iuh

iu_client was original written to have an abstraction
for Iu. However the MSC stopped using iu_client a long
time ago because the abstraption didn't fit well.
There was never time to rewrite SGSN to direct talk RANAP
using the primitives.
Adopt iu_client for now, but with the plan to rewrite
it in a similar way as osmo-msc is doing IuCS.

Adopted from osmo-iuh:
1631c8ac5a2f ("iu_client: fix linter issues")
Related: OS#5487

Change-Id: I9c0d9667ddcb57b52eae34da942acfc1688c1418

include/osmocom/sgsn/Makefile.am

@@ -27,6 +27,7 @@ noinst_HEADERS = \
 	gtp.h \
 	gtp_ggsn.h \
 	gtp_mme.h \
+	iu_client.h \
 	mmctx.h \
 	pdpctx.h \
 	sgsn.h \

include/osmocom/sgsn/iu_client.h

@@ -0,0 +1,103 @@
+#pragma once
+
+#include <stdbool.h>
+
+#include <osmocom/core/defs.h>
+#include <osmocom/core/linuxlist.h>
+#include <osmocom/gsm/gsm48.h>
+#include <osmocom/iuh/common.h>
+#include <osmocom/ranap/ranap_common.h>
+#include <osmocom/ranap/vty.h>
+#include <osmocom/sigtran/sccp_sap.h>
+
+struct msgb;
+struct osmo_auth_vector;
+
+struct RANAP_RAB_SetupOrModifiedItemIEs_s;
+struct RANAP_Cause;
+
+struct ranap_iu_rnc;
+
+struct ranap_ue_conn_ctx {
+	struct llist_head list;
+	struct ranap_iu_rnc *rnc;
+	uint32_t conn_id;
+	int integrity_active;
+	struct gprs_ra_id ra_id;
+	enum ranap_nsap_addr_enc rab_assign_addr_enc;
+	bool notification; /* send notification to the upstream user */
+	/* if true the ue_ctx will be free on Iu release complete */
+	bool free_on_release;
+	/* Will be set when the Iu Release Command has been sent */
+	struct osmo_timer_list release_timeout;
+};
+
+enum ranap_iu_event_new_area_type {
+	RANAP_IU_NEW_LAC,
+	RANAP_IU_NEW_RAC,
+};
+
+struct ranap_iu_event_new_area {
+	const struct osmo_rnc_id *rnc_id;
+	enum ranap_iu_event_new_area_type cell_type;
+	union {
+		const struct osmo_location_area_id *lai;
+		const struct osmo_routing_area_id *rai;
+	} u;
+};
+
+enum ranap_iu_event_type {
+	RANAP_IU_EVENT_RAB_ASSIGN,
+	RANAP_IU_EVENT_SECURITY_MODE_COMPLETE,
+	RANAP_IU_EVENT_IU_RELEASE, /* An actual Iu Release message was received */
+	RANAP_IU_EVENT_LINK_INVALIDATED, /* A SUA link was lost or closed down */
+	RANAP_IU_EVENT_NEW_AREA, /* Either a new LAC/RAC has been detected */
+};
+
+extern const struct value_string ranap_iu_event_type_names[];
+static inline const char *ranap_iu_event_type_str(enum ranap_iu_event_type e)
+{
+	return get_value_string(ranap_iu_event_type_names, e);
+}
+
+/* Implementations of iu_recv_cb_t shall find the ranap_ue_conn_ctx in msg->dst. */
+typedef int (*ranap_iu_recv_cb_t)(struct msgb *msg, struct gprs_ra_id *ra_id,
+				  uint16_t *sai);
+
+typedef int (*ranap_iu_event_cb_t)(struct ranap_ue_conn_ctx *ue_ctx,
+				   enum ranap_iu_event_type type, void *data);
+
+typedef int (*ranap_iu_rab_ass_resp_cb_t)(struct ranap_ue_conn_ctx *ue_ctx, uint8_t rab_id,
+					  struct RANAP_RAB_SetupOrModifiedItemIEs_s *setup_ies);
+
+int ranap_iu_init(void *ctx, int log_subsystem, const char *sccp_user_name, struct osmo_sccp_instance *sccp,
+		  ranap_iu_recv_cb_t iu_recv_cb, ranap_iu_event_cb_t iu_event_cb);
+
+int ranap_iu_tx(struct msgb *msg, uint8_t sapi);
+
+int ranap_iu_page_cs(const char *imsi, const uint32_t *tmsi, uint16_t lac)
+	OSMO_DEPRECATED("Use ranap_iu_page_cs2 instead");
+
+int ranap_iu_page_ps(const char *imsi, const uint32_t *ptmsi, uint16_t lac, uint8_t rac)
+	OSMO_DEPRECATED("Use ranap_iu_page_ps2 instead");
+
+int ranap_iu_page_cs2(const char *imsi, const uint32_t *tmsi, const struct osmo_location_area_id *lai);
+int ranap_iu_page_ps2(const char *imsi, const uint32_t *ptmsi, const struct osmo_routing_area_id *rai);
+
+int ranap_iu_rab_act(struct ranap_ue_conn_ctx *ue_ctx, struct msgb *msg);
+int ranap_iu_rab_deact(struct ranap_ue_conn_ctx *ue_ctx, uint8_t rab_id);
+int ranap_iu_tx_sec_mode_cmd(struct ranap_ue_conn_ctx *uectx, struct osmo_auth_vector *vec,
+			     int send_ck, int new_key);
+int ranap_iu_tx_common_id(struct ranap_ue_conn_ctx *ue_ctx, const char *imsi);
+int ranap_iu_tx_release(struct ranap_ue_conn_ctx *ctx, const struct RANAP_Cause *cause);
+
+/* Transmit a Iu Release Command and submit event RANAP_IU_EVENT_IU_RELEASE upon
+ * Release Complete or timeout. Caller is responsible to free the context and
+ * closing the SCCP connection (ranap_iu_free_ue) upon recieval of the event. */
+void ranap_iu_tx_release_free(struct ranap_ue_conn_ctx *ctx,
+			      const struct RANAP_Cause *cause,
+			      int timeout);
+
+/* freeing the UE will release all resources
+ * This will close the SCCP connection connected to the UE */
+void ranap_iu_free_ue(struct ranap_ue_conn_ctx *ue_ctx);