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route_table: Introduce ss7_route_table_dpc_is_accessible() API

In some places we don't need to select/choose a specific route (hence
requiring a loadshare decision and hence modifying state), but simply
figure out whether there's an available route for a given rmeote PC.

Change-Id: Ia3b2eb17afae71dc7cec34b521693e776fa3576d
---
M src/sccp_scrc.c
M src/ss7_route_table.c
M src/ss7_route_table.h
M src/xua_snm.c
4 files changed, 29 insertions(+), 25 deletions(-)

diff --git a/src/sccp_scrc.c b/src/sccp_scrc.c
index ebc9a11..d7a6428 100644
--- a/src/sccp_scrc.c
+++ b/src/sccp_scrc.c
@@ -70,9 +70,8 @@
 static bool dpc_accessible(struct osmo_sccp_instance *inst, uint32_t dpc)
 {
 	struct osmo_ss7_instance *ss7 = inst->ss7;
-	struct osmo_ss7_route *rt;
-	struct osmo_ss7_route_label rtlabel;
 	char buf_dpc[MAX_PC_STR_LEN];
+	bool found;
 
 	if (osmo_ss7_pc_is_local(ss7, dpc)) {
 		LOGPSCI(inst, LOGL_DEBUG, "dpc_accessible(DPC=%u=%s): true (local)\n",
@@ -80,22 +79,14 @@
 		return true;
 	}
 
-	rtlabel = (struct osmo_ss7_route_label){
-		.opc = 0,
-		.dpc = dpc,
-		.sls = 0,
-	};
+	found = ss7_route_table_dpc_is_accessible(ss7->rtable_system, dpc);
 
-	rt = ss7_instance_lookup_route(ss7, &rtlabel);
-	if (!rt) {
-		LOGPSCI(inst, LOGL_INFO, "dpc_accessible(DPC=%u=%s): false\n",
-			dpc, osmo_ss7_pointcode_print_buf(buf_dpc, sizeof(buf_dpc), ss7, dpc));
-		return false;
-	}
+	LOGPSCI(inst, found ? LOGL_DEBUG : LOGL_INFO,
+		"dpc_accessible(DPC=%u=%s): %s\n",
+		dpc, osmo_ss7_pointcode_print_buf(buf_dpc, sizeof(buf_dpc), ss7, dpc),
+		found ? "true" : "false");
+	return found;
 
-	LOGPSCI(inst, LOGL_DEBUG, "dpc_accessible(DPC=%u=%s): true\n",
-		dpc, osmo_ss7_pointcode_print_buf(buf_dpc, sizeof(buf_dpc), ss7, dpc));
-	return true;
 }
 
 static bool sccp_available(struct osmo_sccp_instance *inst,
diff --git a/src/ss7_route_table.c b/src/ss7_route_table.c
index bd7b305..16eb9bd 100644
--- a/src/ss7_route_table.c
+++ b/src/ss7_route_table.c
@@ -299,6 +299,8 @@
 	}
 }
 
+/* Choose a specific route to transmit a packet.
+ * Note: This function potentially modifies loadsharing state context of chosen combined linkset. */
 struct osmo_ss7_route *
 ss7_route_table_lookup_route(const struct osmo_ss7_route_table *rtbl, const struct osmo_ss7_route_label *rtlabel)
 {
@@ -322,3 +324,20 @@
 	}
 	return NULL;
 }
+
+/* Figure out whether a remote PC is accessible over any route in the routing table.
+ * Note: Unlike ss7_route_table_lookup_route(), this function is read-only and doesn't modify any state. */
+bool ss7_route_table_dpc_is_accessible(const struct osmo_ss7_route_table *rtbl, uint32_t dpc)
+{
+	struct osmo_ss7_combined_linkset *clset;
+	/* we assume the combined_links are sorted by mask length, i.e. more
+	 * specific combined links first, and less specific combined links with shorter
+	 * mask later */
+	llist_for_each_entry(clset, &rtbl->combined_linksets, list) {
+		if ((dpc & clset->cfg.mask) != clset->cfg.pc)
+			continue;
+		if (ss7_combined_linkset_is_available(clset))
+			return true;
+	}
+	return false;
+}
diff --git a/src/ss7_route_table.h b/src/ss7_route_table.h
index 5141c18..582a8d3 100644
--- a/src/ss7_route_table.h
+++ b/src/ss7_route_table.h
@@ -46,6 +46,7 @@
 				       uint32_t mask, const struct osmo_ss7_as *as, bool dynamic);
 struct osmo_ss7_route *
 ss7_route_table_lookup_route(const struct osmo_ss7_route_table *rtbl, const struct osmo_ss7_route_label *rtlabel);
+bool ss7_route_table_dpc_is_accessible(const struct osmo_ss7_route_table *rtbl, uint32_t dpc);
 
 struct osmo_ss7_combined_linkset *
 ss7_route_table_find_combined_linkset(const struct osmo_ss7_route_table *rtbl, uint32_t dpc, uint32_t mask, uint32_t prio);
diff --git a/src/xua_snm.c b/src/xua_snm.c
index d4c9a75..207b042 100644
--- a/src/xua_snm.c
+++ b/src/xua_snm.c
@@ -375,16 +375,10 @@
 		uint8_t mask = _aff_pc >> 24;
 		bool is_available;
 
-		struct osmo_ss7_route_label rtlabel = {
-			.opc = xua->mtp.opc, /* Use OPC of received DAUD. */
-			.dpc = pc,
-			.sls = 0,
-		};
-
 		if (mask == 0) {
 			/* one single point code */
 			/* Check if there's an "active" route available: */
-			is_available = !!ss7_instance_lookup_route(s7i, &rtlabel);
+			is_available = ss7_route_table_dpc_is_accessible(s7i->rtable_system, pc);
 
 			xua_tx_snm_available(asp, rctx, num_rctx, &aff_pc[i], 1, "Response to DAUD",
 					     is_available);
@@ -397,8 +391,7 @@
 			uint32_t *aff_pc_avail = talloc_size(asp, sizeof(uint32_t)*(1 << mask));
 			uint32_t *aff_pc_unavail = talloc_size(asp, sizeof(uint32_t)*(1 << mask));
 			for (fullpc = (pc & ~maskbits); fullpc <= (pc | maskbits); fullpc++) {
-				rtlabel.dpc = fullpc;
-				is_available = !!ss7_instance_lookup_route(s7i, &rtlabel);
+				is_available = ss7_route_table_dpc_is_accessible(s7i->rtable_system, fullpc);
 				if (is_available)
 					aff_pc_avail[num_aff_pc_avail++] = htonl(fullpc); /* mask = 0 */
 				else

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