mscsplit: various preparations to separate MSC from BSC

Disable large parts of the code that depend on BSC presence.

Don't set msg->lchan nor msg->dst.
Don't use lchan in libmsc.
Decouple lac from bts.

Prepare entry/exit point for MSC -> BSC and MSC -> RNC communication:
Add msc_ifaces.[hc], a_iface.c, with a general msc_tx_dtap() to redirect to
different interfaces depending on the actual subscriber connection.
While iu_tx() is going to be functional fairly soon, the a_tx() is going to be
just a dummy for some time (see comment).
Add Iu specific fields in gsm_subscriber_connection: the UE connection pointer
and an indicator for the Integrity Protection status on Iu (to be fully
implemented in later commits).
Add lac member to gsm_subscriber_connection, to allow decoupling from
bts->location_area_code. The conn->lac will actually be set in iu.c in an
upcoming commit ("add iucs.[hc]").

move to libcommon-cs: gsm48_extract_mi(), gsm48_paging_extract_mi().

libmsc: duplicate gsm0808 / gsm48 functions (towards BSC).
In osmo-nitb, libmsc would directly call the functions on the BSC level, not
always via the bsc_api. When separating libmsc from libbsc, some functions are
missing from the linkage.
Hence duplicate these functions to libmsc, add an msc_ prefix for clarity, also
add a _tx to gsm0808_cipher_mode():
* add msc_gsm0808_tx_cipher_mode() (dummy/stub)
* add msc_gsm48_tx_mm_serv_ack()
* add msc_gsm48_tx_mm_serv_rej()
Call these from libmsc instead of
* gsm0808_cipher_mode()
* gsm48_tx_mm_serv_ack()
* gsm48_tx_mm_serv_rej()
Also add a comment related to msc_gsm0808_tx_cipher_mode() in two places.

Temporarily disable all paging to be able to link libmsc without libbsc.
Skip the paging part of channel_test because the paging is now disabled.
In osmo-nitb, paging is done on BSC level and MSC level "at the same time".
When the new MSC is fully operational, paging will be controlled separately on
the MSC level, and the BSC (RNC) level will be instructed over an IuCS or
A-interface to negotiate paging with the MS (UE). This MSC level paging does
not yet exist and will be added in subsequent commits.

msc_compl_l3(): publish in .h, tweak return value.  Use new libmsc enum values
for return val, to avoid dependency on libbsc headers.  Make callable from
other scopes: publish in osmo_msc.h and remove 'static' in osmo_msc.c

add gsm_encr to subscr_conn
move subscr_request to gsm_subscriber.h
subscr_request_channel() -> subscr_request_conn()
move to libmsc: osmo_stats_vty_add_cmds()
gsm_04_08: remove apply_codec_restrictions()
gsm0408_test: use NULL for root ctx
move to libbsc: gsm_bts_neighbor()
move to libbsc: lchan_next_meas_rep()
move vty config for t3212 to network level (periodic lu)
remove unneccessary linking from some tests
remove handle_abisip_signal()
abis_rsl.c: don't use libvlr from libbsc

Change-Id: I9cf80f9c2c8a53a29e42f000029e680a9922cb41

1 files changed, 47 insertions, 0 deletions

diff --git a/openbsc/include/openbsc/msc_ifaces.h b/openbsc/include/openbsc/msc_ifaces.h
new file mode 100644
index 000000000..83aad92a4
--- /dev/null
+++ b/openbsc/include/openbsc/msc_ifaces.h
@@ -0,0 +1,47 @@
+#pragma once
+
+#include <osmocom/core/msgb.h>
+#include <openbsc/gsm_data.h>
+
+/* These are the interfaces of the MSC layer towards (from?) the BSC and RNC,
+ * i.e. in the direction towards the mobile device (MS aka UE).
+ *
+ * 2G will use the A-interface,
+ * 3G aka UMTS will use the Iu-interface (for the MSC, it's IuCS).
+ *
+ * To allow linking parts of the MSC code without having to include entire
+ * infrastructures of external libraries, the core transmitting and receiving
+ * functions are left unimplemented. For example, a unit test does not need to
+ * link against external ASN1 libraries if it is never going to encode actual
+ * outgoing messages. It is up to each building scope to implement real world
+ * functions or to plug mere dummy implementations.
+ *
+ * For example, msc_tx_dtap(conn, msg), depending on conn->via_iface, will call
+ * either iu_tx() or a_tx() [note: at time of writing, the A-interface is not
+ * yet implemented]. When you try to link against libmsc, you will find that
+ * the compiler complains about an undefined reference to iu_tx(). If you,
+ * however, link against libiu as well as the osmo-iuh libs (etc.), iu_tx() is
+ * available. A unit test may instead simply implement a dummy iu_tx() function
+ * and not link against osmo-iuh.
+ */
+
+/* Each main linkage must implement this function (see comment above). */
+extern int iu_tx(struct msgb *msg, uint8_t sapi);
+
+/* So far this is a dummy implemented in libmsc/a_iface.c. When A-interface
+ * gets implemented, it should be in a separate lib (like libiu), this function
+ * should move there, and the following comment should remain here: "
+ * Each main linkage must implement this function (see comment above).
+ * " */
+extern int a_tx(struct msgb *msg);
+
+int msc_tx_dtap(struct gsm_subscriber_connection *conn,
+		struct msgb *msg);
+
+int msc_gsm48_tx_mm_serv_ack(struct gsm_subscriber_connection *conn);
+int msc_gsm48_tx_mm_serv_rej(struct gsm_subscriber_connection *conn,
+			     enum gsm48_reject_value value);
+
+/* TODO: specific to A interface, move this away */
+int msc_gsm0808_tx_cipher_mode(struct gsm_subscriber_connection *conn, int cipher,
+			       const uint8_t *key, int len, int include_imeisv);