add gsm0808_{enc,dec}_cell_id

Clarify semantics and micro-optimise for the case of single Cell Identifer IEs.
Test in gsm0808_test.c

So far we have gsm0808_enc_cell_id_list2(), but there also exist instances of
single Cell Identifiers (3GPP TS 48.008 3.2.2.17).

It is possible to decode the same using the cell identifier list API, but this
forces the caller to also keep a full struct gsm0808_cell_id_list2 with all its
127 entries around.

E.g. for handover, there are two Cell Identifiers (Serving and Target); I'd
need two full cell id lists for each, and these would be dynamically allocated
for each handover operation, whether it uses them or not.

Related: OS#2283 (inter-BSC HO, BSC side)
Change-Id: I9f9c528965775698ab62ac386af0516192c4b0cc

1 files changed, 21 insertions, 12 deletions

diff --git a/include/osmocom/gsm/gsm0808_utils.h b/include/osmocom/gsm/gsm0808_utils.h
index 34eae438..8e71b43c 100644
--- a/include/osmocom/gsm/gsm0808_utils.h
+++ b/include/osmocom/gsm/gsm0808_utils.h
@@ -31,20 +31,27 @@ struct sockaddr_storage;
  /*! (225-1)/2 is the maximum number of elements in a cell identifier list. */
 #define GSM0808_CELL_ID_LIST2_MAXLEN		127
 
-/*! Parsed representation of a cell identifier list IE. */
+/*! Instead of this, use either struct gsm0808_cell_id or gsm0808_cell_id_list2.
+ * All elements contain parsed representations of the data in the corresponding IE, in host-byte order.
+ */
+union gsm0808_cell_id_u {
+	struct osmo_cell_global_id		global;
+	struct osmo_lac_and_ci_id		lac_and_ci;
+	uint16_t				ci;
+	struct osmo_location_area_id		lai_and_lac;
+	uint16_t				lac;
+};
+
+/*! Parsed representation of Cell Identifier IE (3GPP TS 48.008 3.2.2.17) */
+struct gsm0808_cell_id {
+	enum CELL_IDENT id_discr;
+	union gsm0808_cell_id_u id;
+};
+
+/*! Parsed representation of a Cell Identifier List IE (3GPP TS 48.008 3.2.2.27). */
 struct gsm0808_cell_id_list2 {
 	enum CELL_IDENT id_discr;
-	union {
-		/*!
-		 * All elements of these arrays contain parsed representations of the
-		 * data in the corresponding IE, in host-byte order.
-		 */
-		struct osmo_cell_global_id		global;
-		struct osmo_lac_and_ci_id		lac_and_ci;
-		uint16_t				ci;
-		struct osmo_location_area_id		lai_and_lac;
-		uint16_t				lac;
-	} id_list[GSM0808_CELL_ID_LIST2_MAXLEN];
+	union gsm0808_cell_id_u id_list[GSM0808_CELL_ID_LIST2_MAXLEN];
 	unsigned int id_list_len;
 };
 
@@ -78,6 +85,8 @@ int gsm0808_dec_cell_id_list(struct gsm0808_cell_id_list *cil,
 			     const uint8_t *elem, uint8_t len)
 			     OSMO_DEPRECATED("use gsm0808_dec_cell_id_list2 instead");
 int gsm0808_cell_id_list_add(struct gsm0808_cell_id_list2 *dst, const struct gsm0808_cell_id_list2 *src);
+uint8_t gsm0808_enc_cell_id(struct msgb *msg, const struct gsm0808_cell_id *ci);
+int gsm0808_dec_cell_id(struct gsm0808_cell_id *ci, const uint8_t *elem, uint8_t len);
 int gsm0808_chan_type_to_speech_codec(uint8_t perm_spch);
 int gsm0808_speech_codec_from_chan_type(struct gsm0808_speech_codec *sc,
 					uint8_t perm_spch);