usrloc: Add urecord reference counting mechanism

This mechanism is required by the mid-registrar, which needs to
"reserve" contact IDs while the main registrar decides upon them.
This means that a blank urecord structure must be kept alive during
this process.

By reference counting the blank urecord structures, we prevent them
from being cleared by the timer before the outgoing registrations
get a chance to receive a reply.

(cherry picked from commit ad274fa)

modules/usrloc/udomain.c

@@ -1156,7 +1156,7 @@ int mem_timer_udomain(udomain_t* _d)
 				flush=1;
 
 			/* Remove the entire record if it is empty */
-			if (ptr->contacts == NULL)
+			if (ptr->no_clear_ref <= 0 && ptr->contacts == NULL)
 			{
 				if (exists_ulcb_type(UL_AOR_EXPIRE))
 					run_ul_callbacks(UL_AOR_EXPIRE, ptr);
@@ -1349,9 +1349,6 @@ int delete_urecord(udomain_t* _d, str* _aor, struct urecord* _r,
 		}
 	}
 
-	if (!is_replicated && ul_replicate_cluster)
-		replicate_urecord_delete(_r);
-
 	c = _r->contacts;
 	while(c) {
 		t = c;
@@ -1361,6 +1358,13 @@ int delete_urecord(udomain_t* _d, str* _aor, struct urecord* _r,
 			return -1;
 		}
 	}
+
+	if (_r->no_clear_ref > 0)
+		return 0;
+
+	if (!is_replicated && ul_replicate_cluster)
+		replicate_urecord_delete(_r);
+
 	release_urecord(_r, is_replicated);
 	return 0;
 }

modules/usrloc/urecord.c

@@ -481,7 +481,7 @@ void release_urecord(urecord_t* _r, char is_replicated)
 			LM_ERR("failed to sync with db\n");
 		/* now simply free everything */
 		free_urecord(_r);
-	} else if (_r->contacts == 0) {
+	} else if (_r->no_clear_ref <= 0 && _r->contacts == 0) {
 		if (exists_ulcb_type(UL_AOR_DELETE))
 			run_ul_callbacks(UL_AOR_DELETE, _r);
 

modules/usrloc/urecord.h

@@ -53,12 +53,13 @@ typedef struct urecord {
 	str aor;                       /*!< Address of record */
 	unsigned int aorhash;          /*!< Hash over address of record */
 	unsigned int label;            /*!< Labels over AVL tree */
-	unsigned short next_clabel;      /*!< Labels to be assigned to contacts */
+	unsigned short next_clabel;    /*!< Labels to be assigned to contacts */
 	ucontact_t* contacts;          /*!< One or more contact fields */
 
 	struct hslot* slot;            /*!< Collision slot in the hash table
                                     * array we belong to */
 
+	int no_clear_ref;              /*!< Keep the record while positive */
 	void **attached_data;          /*!< data attached by API subscribers >*/
 } urecord_t;