mgcp client: allow setting conn mode for CRCX and MDCX

Add conn_mode to struct mgcp_conn_peer, to allow setting an explicit connection
mode instead of implicit MGCP_CONN_RECV_ONLY / MGCP_CONN_RECV_SEND depending on
remote RTP port presence. Default to old behavior if this is left unset.

Rationale:

For IuUP Initialization, osmo-msc currently still uses a hack at osmo-mgw to
echo the IuUP Initialization back to the sender as an ACK. For sanity checking
reasons, this is done iff the CRCX created the CI in loopback mode. So, in
order to be able to switch to the mgcp_client_fsm in osmo-msc instead of
"manual" MGCP message composition and yet still be able to support IuUP and
IuCS, we need to be able to set the conn mode upon CRCX to loopback.

If we merged the IuUP patch (which is already on a branch somewhere) to
osmo-mgw, we wouldn't bother with this patch, but adding this conn mode choice
has these benefits:

- post-IuUP-fix osmo-msc versions can interop with older osmo-mgw IuUP for
  IuCS.

- It is conceivable that some MGCP clients prefer explicit conn modes instead
  of the implicit MGCP_CONN_RECV_ONLY / MGCP_CONN_RECV_SEND choice. This opens
  the possibility to switch between conn modes with MDCX messages.

Change-Id: I26be5c4b06a680f25f19797407ab56a5a4880ddc

1 files changed, 4 insertions, 0 deletions

diff --git a/include/osmocom/mgcp_client/mgcp_client_fsm.h b/include/osmocom/mgcp_client/mgcp_client_fsm.h
index bb07872aa..716a6d4ac 100644
--- a/include/osmocom/mgcp_client/mgcp_client_fsm.h
+++ b/include/osmocom/mgcp_client/mgcp_client_fsm.h
@@ -47,6 +47,10 @@ struct mgcp_conn_peer {
 	 * known to issue incoherent or unknown CallIDs / to issue CRCX commands with a different domain
 	 * name than the BSC. An OsmoMGW will then ignore these and not fail on mismatches. */
 	uint32_t x_osmo_ign;
+
+	/*! If left MGCP_CONN_NONE, use MGCP_CONN_RECV_ONLY or MGCP_CONN_RECV_SEND, depending on whether an audio RTP
+	 * address is set. If != MGCP_CONN_NONE, force this conn mode. */
+	enum mgcp_connection_mode conn_mode;
 };
 
 struct osmo_fsm_inst *mgcp_conn_create(struct mgcp_client *mgcp, struct osmo_fsm_inst *parent_fi, uint32_t parent_term_evt,