Create new 'gprs-sgsn' branch on top of 'gprs-conf'

This branch contains the partial SGSN/GGSN implementation that
was originally developed as part of the gprs branch.
diff --git a/openbsc/src/gprs_sgsn.c b/openbsc/src/gprs_sgsn.c
new file mode 100644
index 0000000..477e448
--- /dev/null
+++ b/openbsc/src/gprs_sgsn.c
@@ -0,0 +1,93 @@
+/* GPRS SGSN functionality */
+
+/* (C) 2009 by Harald Welte <laforge@gnumonks.org>
+ *
+ * All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+#include <sys/types.h>
+
+#include <osmocore/linuxlist.h>
+#include <osmocore/talloc.h>
+#include <osmocore/timer.h>
+#include <openbsc/gsm_subscriber.h>
+#include <openbsc/gprs_sgsn.h>
+
+static LLIST_HEAD(sgsn_mm_ctxts);
+
+static int ra_id_equals(const struct gprs_ra_id *id1,
+			const struct gprs_ra_id *id2)
+{
+	return (id1->mcc == id2->mcc && id1->mnc == id2->mnc &&
+		id1->lac == id2->lac && id1->rac == id2->rac);
+}
+
+/* look-up a SGSN MM context based on TLLI + RAI */
+struct sgsn_mm_ctx *sgsn_mm_ctx_by_tlli(u_int32_t tlli,
+					const struct gprs_ra_id *raid)
+{
+	struct sgsn_mm_ctx *ctx;
+
+	llist_for_each_entry(ctx, &sgsn_mm_ctxts, list) {
+		if (tlli == ctx->tlli &&
+		    ra_id_equals(raid, &ctx->ra))
+			return ctx;
+	}
+	return NULL;
+}
+
+struct sgsn_mm_ctx *sgsn_mm_ctx_by_ptmsi(u_int32_t p_tmsi)
+{
+	struct sgsn_mm_ctx *ctx;
+
+	llist_for_each_entry(ctx, &sgsn_mm_ctxts, list) {
+		if (p_tmsi == ctx->p_tmsi)
+			return ctx;
+	}
+	return NULL;
+}
+
+struct sgsn_mm_ctx *sgsn_mm_ctx_by_imsi(const char *imsi)
+{
+	struct sgsn_mm_ctx *ctx;
+
+	llist_for_each_entry(ctx, &sgsn_mm_ctxts, list) {
+		if (!strcmp(imsi, ctx->imsi))
+			return ctx;
+	}
+	return NULL;
+
+}
+
+/* Allocate a new SGSN MM context */
+struct sgsn_mm_ctx *sgsn_mm_ctx_alloc(u_int32_t tlli,
+					const struct gprs_ra_id *raid)
+{
+	struct sgsn_mm_ctx *ctx = talloc_zero(NULL, struct sgsn_mm_ctx);
+
+	if (!ctx)
+		return NULL;
+
+	memcpy(&ctx->ra, raid, sizeof(ctx->ra));
+	ctx->tlli = tlli;
+	ctx->mm_state = GMM_DEREGISTERED;
+
+	llist_add(&ctx->list, &sgsn_mm_ctxts);
+
+	return ctx;
+}