create libosmoisdn sub-library

There are some parts of libosmogsm which are not really GSM specific,
but rather ISDN bits that were inherited by GSM.  This includes the
I.460 multiplex as well as the core LAPD protocol.

Let's move those bits to its own libosmoisdn library, before we add
more ISDN specific bits to the wrong place.

Backwards-compatibility is created by making libosmogsm depend on
libosmoisdn, and by providing wrapper include files for source
compatibility.

Change-Id: Ib1a6c762322fd5047be3188b1df22408ef06aa50
diff --git a/include/osmocom/isdn/lapd_core.h b/include/osmocom/isdn/lapd_core.h
new file mode 100644
index 0000000..e4e8b46
--- /dev/null
+++ b/include/osmocom/isdn/lapd_core.h
@@ -0,0 +1,176 @@
+/*! \file lapd_core.h
+ * primitive related stuff
+ */
+#pragma once
+
+#include <stdint.h>
+
+#include <osmocom/core/timer.h>
+#include <osmocom/core/msgb.h>
+#include <osmocom/gsm/prim.h>
+
+/*! \defgroup lapd LAPD implementation common part
+ *  @{
+ * \file lapd_core.h
+ */
+
+#define LOGDL(dl, level, fmt, args...) \
+	LOGP(DLLAPD, level, "(%s) "  fmt, (dl)->name, ## args)
+
+/*! LAPD related primitives (L2<->L3 SAP)*/
+enum osmo_dl_prim {
+	PRIM_DL_UNIT_DATA,	/*!< DL-UNIT-DATA */
+	PRIM_DL_DATA,		/*!< DL-DATA */
+	PRIM_DL_EST,		/*!< DL-ESTABLISH */
+	PRIM_DL_REL,		/*!< DL-RLEEASE */
+	PRIM_DL_SUSP,		/*!< DL-SUSPEND */
+	PRIM_DL_RES,		/*!< DL-RESUME */
+	PRIM_DL_RECON,		/*!< DL-RECONNECT */
+	PRIM_MDL_ERROR,		/*!< MDL-ERROR */
+};
+
+/* Uses the same values as RLL, so no conversion for GSM is required. */
+#define MDL_CAUSE_T200_EXPIRED		0x01
+#define MDL_CAUSE_REEST_REQ		0x02
+#define MDL_CAUSE_UNSOL_UA_RESP		0x03
+#define MDL_CAUSE_UNSOL_DM_RESP		0x04
+#define MDL_CAUSE_UNSOL_DM_RESP_MF	0x05
+#define MDL_CAUSE_UNSOL_SPRV_RESP	0x06
+#define MDL_CAUSE_SEQ_ERR		0x07
+#define MDL_CAUSE_UFRM_INC_PARAM	0x08
+#define MDL_CAUSE_SFRM_INC_PARAM	0x09
+#define MDL_CAUSE_IFRM_INC_MBITS	0x0a
+#define MDL_CAUSE_IFRM_INC_LEN		0x0b
+#define MDL_CAUSE_FRM_UNIMPL		0x0c
+#define MDL_CAUSE_SABM_MF		0x0d
+#define MDL_CAUSE_SABM_INFO_NOTALL	0x0e
+#define MDL_CAUSE_FRMR			0x0f
+
+/*! for MDL-ERROR.ind */
+struct mdl_error_ind_param {
+	uint8_t cause;		/*!< generic cause value */
+};
+
+/*! for DL-REL.req */
+struct dl_rel_req_param {
+	uint8_t mode;		/*!< release mode */
+};
+
+/*! primitive header for LAPD DL-SAP primitives */
+struct osmo_dlsap_prim {
+	struct osmo_prim_hdr oph; /*!< generic primitive header */
+	union {
+		struct mdl_error_ind_param error_ind;
+		struct dl_rel_req_param rel_req;
+	} u;			/*!< request-specific data */
+};
+
+/*! LAPD mode/role */
+enum lapd_mode {
+	LAPD_MODE_USER,		/*!< behave like user */
+	LAPD_MODE_NETWORK,	/*!< behave like network */
+};
+
+/*! LAPD state (Figure B.2/Q.921)*/
+enum lapd_state {
+	LAPD_STATE_NULL = 0,
+	LAPD_STATE_TEI_UNASS,
+	LAPD_STATE_ASS_TEI_WAIT,
+	LAPD_STATE_EST_TEI_WAIT,
+	LAPD_STATE_IDLE,
+	LAPD_STATE_SABM_SENT,
+	LAPD_STATE_DISC_SENT,
+	LAPD_STATE_MF_EST,
+	LAPD_STATE_TIMER_RECOV,
+};
+
+/*! LAPD message format (I / S / U) */
+enum lapd_format {
+	LAPD_FORM_UKN = 0,
+	LAPD_FORM_I,
+	LAPD_FORM_S,
+	LAPD_FORM_U,
+};
+
+/*! LAPD message context */
+struct lapd_msg_ctx {
+	struct lapd_datalink *dl;
+	int n201;
+	/* address */
+	uint8_t cr;
+	uint8_t sapi;
+	uint8_t tei;
+	uint8_t lpd;
+	/* control */
+	uint8_t format;
+	uint8_t p_f; /* poll / final bit */
+	uint8_t n_send;
+	uint8_t n_recv;
+	uint8_t s_u; /* S or repectivly U function bits */
+	/* length */
+	int	length;
+	uint8_t	more;
+};
+
+struct lapd_cr_ent {
+	uint8_t cmd;
+	uint8_t resp;
+};
+
+struct lapd_history {
+	struct msgb *msg; /* message to be sent / NULL, if histoy is empty */
+	int	more; /* if message is fragmented */
+};
+
+/*! LAPD datalink */
+struct lapd_datalink {
+	int (*send_dlsap)(struct osmo_dlsap_prim *dp, struct lapd_msg_ctx *lctx);
+	int (*send_ph_data_req)(struct lapd_msg_ctx *lctx, struct msgb *msg);
+	int (*update_pending_frames)(struct lapd_msg_ctx *lctx);
+	struct {
+		/*! filled-in once we set the lapd_mode above */
+		struct lapd_cr_ent loc2rem;
+		struct lapd_cr_ent rem2loc;
+	} cr;
+	enum lapd_mode mode; /*!< current mode of link */
+	int use_sabme; /*!< use SABME instead of SABM */
+	int reestablish; /*!< enable reestablish support */
+	int n200, n200_est_rel; /*!< number of retranmissions */
+	struct lapd_msg_ctx lctx; /*!< LAPD context */
+	int maxf; /*!< maximum frame size (after defragmentation) */
+	uint8_t k; /*!< maximum number of unacknowledged frames */
+	uint8_t v_range; /*!< range of sequence numbers */
+	uint8_t v_send;	/*!< seq nr of next I frame to be transmitted */
+	uint8_t v_ack;	/*!< last frame ACKed by peer */
+	uint8_t v_recv;	/*!< seq nr of next I frame expected to be received */
+	uint32_t state; /*!< LAPD state (\ref lapd_state) */
+	int seq_err_cond; /*!< condition of sequence error */
+	uint8_t own_busy; /*!< receiver busy on our side */
+	uint8_t peer_busy; /*!< receiver busy on remote side */
+	int t200_sec, t200_usec; /*!< retry timer (default 1 sec) */
+	int t203_sec, t203_usec; /*!< retry timer (default 10 secs) */
+	struct osmo_timer_list t200; /*!< T200 timer */
+	struct osmo_timer_list t203; /*!< T203 timer */
+	uint8_t retrans_ctr; /*!< re-transmission counter */
+	struct llist_head tx_queue; /*!< frames to L1 */
+	struct llist_head send_queue; /*!< frames from L3 */
+	struct msgb *send_buffer; /*!< current frame transmitting */
+	int send_out; /*!< how much was sent from send_buffer */
+	struct lapd_history *tx_hist; /*!< tx history structure array */
+	uint8_t range_hist; /*!< range of history buffer 2..2^n */
+	struct msgb *rcv_buffer; /*!< buffer to assemble the received message */
+	struct msgb *cont_res; /*!< buffer to store content resolution data on network side, to detect multiple phones on same channel */
+	char *name; /*!< user-provided name */
+};
+
+void lapd_dl_init(struct lapd_datalink *dl, uint8_t k, uint8_t v_range, int maxf)
+	OSMO_DEPRECATED("Use lapd_dl_init2() instead");
+void lapd_dl_init2(struct lapd_datalink *dl, uint8_t k, uint8_t v_range, int maxf, const char *name);
+void lapd_dl_set_name(struct lapd_datalink *dl, const char *name);
+void lapd_dl_exit(struct lapd_datalink *dl);
+void lapd_dl_reset(struct lapd_datalink *dl);
+int lapd_set_mode(struct lapd_datalink *dl, enum lapd_mode mode);
+int lapd_ph_data_ind(struct msgb *msg, struct lapd_msg_ctx *lctx);
+int lapd_recv_dlsap(struct osmo_dlsap_prim *dp, struct lapd_msg_ctx *lctx);
+
+/*! @} */