mobile: add audio config, with unused audio loopback setting

The aim is to add configurable audio loopback to mobile. An existing patch on a
branch from fixeria [1] adds the audio config section. Add a reduced version of
this audio config to be compatible with the future merge.

Add the audio loopback setting, so far without functionality.
Subsequent patch adds the actual loopback.

[1] osmocom-bb branch fixeria/audio,
    patch "mobile/vty_interface.c: add new 'audio' section"
    Change-id I62cd5ef22ca2290fcafe65c78537ddbcb39fb8c6

Change-Id: Ie03e4a6c6f81ea3925266dd22e87506d722a6e1a

doc/examples/mobile/default.cfg

@@ -59,4 +59,6 @@ ms 1
   ki comp128 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
   no barred-access
   rplmn 001 01
+ audio
+  io-handler none
  no shutdown

doc/examples/mobile/multi_ms.cfg

@@ -59,6 +59,8 @@ ms one
   ki comp128 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
   no barred-access
   rplmn 001 01
+ audio
+  io-handler none
  no shutdown
 !
 ms two
@@ -109,4 +111,6 @@ ms two
   ki comp128 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
   no barred-access
   rplmn 001 01
+ audio
+  io-handler none
  no shutdown

src/host/layer23/include/osmocom/bb/mobile/settings.h

@@ -3,10 +3,29 @@
 
 #define MOB_C7_DEFLT_ANY_TIMEOUT	30
 
+/* TCH frame I/O handler */
+enum audio_io_handler {
+	/* No handler, drop frames */
+	AUDIO_IOH_NONE = 0,
+	/* Return to sender */
+	AUDIO_IOH_LOOPBACK,
+};
+
+extern const struct value_string audio_io_handler_names[];
+static inline const char *audio_io_handler_name(enum audio_io_handler val)
+{ return get_value_string(audio_io_handler_names, val); }
+
+struct audio_settings {
+	enum audio_io_handler	io_handler;
+};
+
 struct gsm_settings {
 	char			layer2_socket_path[128];
 	char			sap_socket_path[128];
 
+	/* Audio settings */
+	struct audio_settings	audio;
+
 	/* IMEI */
 	char			imei[16];
 	char			imeisv[17];

src/host/layer23/include/osmocom/bb/mobile/vty.h

@@ -10,6 +10,7 @@ enum ms_vty_node {
 	MS_NODE = _LAST_OSMOVTY_NODE + 1,
 	TESTSIM_NODE,
 	SUPPORT_NODE,
+	AUDIO_NODE,
 };
 
 int ms_vty_go_parent(struct vty *vty);

src/host/layer23/src/mobile/settings.c

@@ -41,6 +41,9 @@ int gsm_settings_init(struct osmocom_ms *ms)
 	strcpy(set->layer2_socket_path, layer2_socket_path);
 	strcpy(set->sap_socket_path, sap_socket_path);
 
+	/* Audio settings: drop TCH frames by default */
+	set->audio.io_handler = AUDIO_IOH_NONE;
+
 	/* network search */
 	set->plmn_mode = PLMN_MODE_AUTO;
 
@@ -194,3 +197,8 @@ int gsm_random_imei(struct gsm_settings *set)
 	return 0;
 }
 
+const struct value_string audio_io_handler_names[] = {
+	{ AUDIO_IOH_NONE,	"none" },
+	{ AUDIO_IOH_LOOPBACK,	"loopback" },
+	{ 0x00, NULL}
+};

src/host/layer23/src/mobile/vty_interface.c

@@ -65,6 +65,12 @@ struct cmd_node support_node = {
 	1
 };
 
+struct cmd_node audio_node = {
+	AUDIO_NODE,
+	"%s(audio)# ",
+	1
+};
+
 static void print_vty(void *priv, const char *fmt, ...)
 {
 	char buffer[1000];
@@ -1526,6 +1532,10 @@ static void config_write_ms(struct vty *vty, struct osmocom_ms *ms)
 		vty_out(vty, " c7-any-timeout %d%s",
 			set->any_timeout, VTY_NEWLINE);
 
+	vty_out(vty, " audio%s", VTY_NEWLINE);
+	if (!hide_default || set->audio.io_handler != AUDIO_IOH_NONE)
+		vty_out(vty, "  io-handler %s%s", audio_io_handler_name(set->audio.io_handler), VTY_NEWLINE);
+
 	/* no shutdown must be written to config, because shutdown is default */
 	vty_out(vty, " %sshutdown%s", (ms->shutdown != MS_SHUTDOWN_NONE) ? "" : "no ",
 		VTY_NEWLINE);
@@ -2727,6 +2737,46 @@ DEFUN(cfg_test_hplmn, cfg_test_hplmn_cmd, "hplmn-search (everywhere|foreign-coun
 	return CMD_SUCCESS;
 }
 
+/* per audio config */
+DEFUN(cfg_ms_audio, cfg_ms_audio_cmd, "audio",
+	"Configure audio settings")
+{
+	vty->node = AUDIO_NODE;
+	return CMD_SUCCESS;
+}
+
+static int set_audio_io_handler(struct vty *vty, enum audio_io_handler val)
+{
+	struct osmocom_ms *ms = (struct osmocom_ms *) vty->index;
+	struct gsm_settings *set = &ms->settings;
+
+	/* Don't restart on unchanged value */
+	if (val == set->audio.io_handler)
+		return CMD_SUCCESS;
+	set->audio.io_handler = val;
+
+	/* Restart required */
+	vty_restart_if_started(vty, ms);
+
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_ms_audio_io_handler, cfg_ms_audio_io_handler_cmd,
+	"io-handler (loopback|none)",
+	"Set TCH frame I/O handler\n"
+	"Return TCH frame payload back to sender\n"
+	"No handler, drop TCH frames (default)")
+{
+	int val = get_string_value(audio_io_handler_names, argv[0]);
+	return set_audio_io_handler(vty, val);
+}
+
+DEFUN(cfg_ms_audio_no_io_handler, cfg_ms_audio_no_io_handler_cmd,
+	"no io-handler", NO_STR "Disable TCH frame processing")
+{
+	return set_audio_io_handler(vty, AUDIO_IOH_NONE);
+}
+
 DEFUN(cfg_no_shutdown, cfg_ms_no_shutdown_cmd, "no shutdown",
 	NO_STR "Activate and run MS")
 {
@@ -2807,6 +2857,7 @@ int ms_vty_go_parent(struct vty *vty)
 		break;
 	case TESTSIM_NODE:
 	case SUPPORT_NODE:
+	case AUDIO_NODE:
 		vty->node = MS_NODE;
 		break;
 	default:
@@ -2918,6 +2969,7 @@ int ms_vty_init(void)
 	install_element(MS_NODE, &cfg_ms_abbrev_cmd);
 	install_element(MS_NODE, &cfg_ms_no_abbrev_cmd);
 	install_element(MS_NODE, &cfg_ms_testsim_cmd);
+	install_element(MS_NODE, &cfg_ms_audio_cmd);
 	install_element(MS_NODE, &cfg_ms_neighbour_cmd);
 	install_element(MS_NODE, &cfg_ms_no_neighbour_cmd);
 	install_element(MS_NODE, &cfg_ms_any_timeout_cmd);
@@ -2995,6 +3047,10 @@ int ms_vty_init(void)
 	install_element(MS_NODE, &cfg_ms_script_load_run_cmd);
 	install_element(MS_NODE, &cfg_ms_no_script_load_run_cmd);
 
+	install_node(&audio_node, config_write_dummy);
+	install_element(AUDIO_NODE, &cfg_ms_audio_io_handler_cmd);
+	install_element(AUDIO_NODE, &cfg_ms_audio_no_io_handler_cmd);
+
 	/* Register the talloc context introspection command */
 	osmo_talloc_vty_add_cmds();