diff --git a/openbsc/src/libbsc/bsc_subscriber.c b/openbsc/src/libbsc/bsc_subscriber.c
new file mode 100644
index 0000000..a5e40cd
--- /dev/null
+++ b/openbsc/src/libbsc/bsc_subscriber.c
@@ -0,0 +1,168 @@
+/* GSM subscriber details for use in BSC land */
+
+/*
+ * (C) 2016 by sysmocom s.f.m.c. GmbH <info@sysmocom.de>
+ *
+ * Author: Neels Hofmeyr <nhofmeyr@sysmocom.de>
+ *
+ * All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include <talloc.h>
+#include <string.h>
+#include <limits.h>
+
+#include <osmocom/gsm/gsm48.h>
+#include <osmocom/core/logging.h>
+
+#include <openbsc/bsc_subscriber.h>
+#include <openbsc/debug.h>
+
+static struct bsc_subscr *bsc_subscr_alloc(struct llist_head *list)
+{
+	struct bsc_subscr *bsub;
+
+	bsub = talloc_zero(list, struct bsc_subscr);
+	if (!bsub)
+		return NULL;
+
+	llist_add_tail(&bsub->entry, list);
+	bsub->use_count = 1;
+
+	return bsub;
+}
+
+struct bsc_subscr *bsc_subscr_find_by_imsi(struct llist_head *list,
+					   const char *imsi)
+{
+	struct bsc_subscr *bsub;
+
+	if (!imsi || !*imsi)
+		return NULL;
+
+	llist_for_each_entry(bsub, list, entry) {
+		if (!strcmp(bsub->imsi, imsi))
+			return bsc_subscr_get(bsub);
+	}
+	return NULL;
+}
+
+struct bsc_subscr *bsc_subscr_find_by_tmsi(struct llist_head *list,
+					   uint32_t tmsi)
+{
+	struct bsc_subscr *bsub;
+
+	if (tmsi == GSM_RESERVED_TMSI)
+		return NULL;
+
+	llist_for_each_entry(bsub, list, entry) {
+		if (bsub->tmsi == tmsi)
+			return bsc_subscr_get(bsub);
+	}
+	return NULL;
+}
+
+void bsc_subscr_set_imsi(struct bsc_subscr *bsub, const char *imsi)
+{
+	if (!bsub)
+		return;
+	strncpy(bsub->imsi, imsi, sizeof(bsub->imsi));
+}
+
+struct bsc_subscr *bsc_subscr_find_or_create_by_imsi(struct llist_head *list,
+						     const char *imsi)
+{
+	struct bsc_subscr *bsub;
+	bsub = bsc_subscr_find_by_imsi(list, imsi);
+	if (bsub)
+		return bsub;
+	bsub = bsc_subscr_alloc(list);
+	bsc_subscr_set_imsi(bsub, imsi);
+	return bsub;
+}
+
+struct bsc_subscr *bsc_subscr_find_or_create_by_tmsi(struct llist_head *list,
+						     uint32_t tmsi)
+{
+	struct bsc_subscr *bsub;
+	bsub = bsc_subscr_find_by_tmsi(list, tmsi);
+	if (bsub)
+		return bsub;
+	bsub = bsc_subscr_alloc(list);
+	bsub->tmsi = tmsi;
+	return bsub;
+}
+
+const char *bsc_subscr_name(struct bsc_subscr *bsub)
+{
+	static char buf[32];
+	if (!bsub)
+		return "unknown";
+	if (bsub->imsi[0])
+		snprintf(buf, sizeof(buf), "IMSI:%s", bsub->imsi);
+	else
+		snprintf(buf, sizeof(buf), "TMSI:0x%08x", bsub->tmsi);
+	return buf;
+}
+
+static void bsc_subscr_free(struct bsc_subscr *bsub)
+{
+	llist_del(&bsub->entry);
+	talloc_free(bsub);
+}
+
+struct bsc_subscr *_bsc_subscr_get(struct bsc_subscr *bsub,
+				   const char *file, int line)
+{
+	OSMO_ASSERT(bsub->use_count < INT_MAX);
+	bsub->use_count++;
+	LOGPSRC(DREF, LOGL_DEBUG, file, line,
+		"BSC subscr %s usage increases to: %d\n",
+		bsc_subscr_name(bsub), bsub->use_count);
+	return bsub;
+}
+
+struct bsc_subscr *_bsc_subscr_put(struct bsc_subscr *bsub,
+				   const char *file, int line)
+{
+	bsub->use_count--;
+	LOGPSRC(DREF, bsub->use_count >= 0? LOGL_DEBUG : LOGL_ERROR,
+		file, line,
+		"BSC subscr %s usage decreases to: %d\n",
+		bsc_subscr_name(bsub), bsub->use_count);
+	if (bsub->use_count <= 0)
+		bsc_subscr_free(bsub);
+	return NULL;
+}
+
+void log_set_filter_bsc_subscr(struct log_target *target,
+			       struct bsc_subscr *bsc_subscr)
+{
+	struct bsc_subscr **fsub = (void*)&target->filter_data[LOG_FLT_BSC_SUBSCR];
+
+	/* free the old data */
+	if (*fsub) {
+		bsc_subscr_put(*fsub);
+		*fsub = NULL;
+	}
+
+	if (bsc_subscr) {
+		target->filter_map |= (1 << LOG_FLT_BSC_SUBSCR);
+		*fsub = bsc_subscr_get(bsc_subscr);
+	} else
+		target->filter_map &= ~(1 << LOG_FLT_BSC_SUBSCR);
+}