chan_dahdi: Add POLARITY function.

Adds a POLARITY function which can be used to
retrieve the current polarity of an FXS channel
as well as set the polarity of an FXS channel
to idle or reverse at any point during a call.

ASTERISK-30000 #close

Change-Id: If6f50998f723e4484bf68e2473f5cedfeaf9b8f1

channels/chan_dahdi.c

@@ -177,6 +177,35 @@
 			<para>This application will Accept the R2 call either with charge or no charge.</para>
 		</description>
 	</application>
+	<function name="POLARITY" language="en_US">
+		<synopsis>
+			Set or get the polarity of a DAHDI channel.
+		</synopsis>
+		<syntax />
+		<description>
+			<para>The POLARITY function can be used to set the polarity of a DAHDI channel.</para>
+			<para>Applies only to FXS channels (using FXO signalling) with supporting hardware.</para>
+			<para>The polarity can be set to the following numeric or named values:</para>
+			<enumlist>
+				<enum name="0" />
+				<enum name="idle" />
+				<enum name="1" />
+				<enum name="reverse" />
+			</enumlist>
+			<para>However, when read, the function will always return 0 or 1.</para>
+			<example title="Set idle polarity">
+			same => n,Set(POLARITY()=0)
+			</example>
+			<example title="Set reverse polarity">
+			same => n,NoOp(Current Polarity: ${POLARITY()})
+			same => n,Set(POLARITY()=reverse)
+			same => n,NoOp(New Polarity: ${POLARITY()})
+			</example>
+			<example title="Reverse the polarity from whatever it is currently">
+			same => n,Set(POLARITY()=${IF($[ "${POLARITY()}" = "1" ]?0:1)})
+			</example>
+		</description>
+	</function>
 	<info name="CHANNEL" language="en_US" tech="DAHDI">
 		<enumlist>
 			<enum name="dahdi_channel">
@@ -2704,6 +2733,86 @@ static void my_hangup_polarityswitch(void *pvt)
 	}
 }
 
+/*! \brief Return DAHDI pivot if channel is FXO signalled */
+static struct dahdi_pvt *fxo_pvt(struct ast_channel *chan)
+{
+	int res;
+	struct dahdi_params dahdip;
+	struct dahdi_pvt *pvt = NULL;
+
+	if (strcasecmp(ast_channel_tech(chan)->type, "DAHDI")) {
+		ast_log(LOG_WARNING, "%s is not a DAHDI channel\n", ast_channel_name(chan));
+		return NULL;
+	}
+
+	memset(&dahdip, 0, sizeof(dahdip));
+	res = ioctl(ast_channel_fd(chan, 0), DAHDI_GET_PARAMS, &dahdip);
+
+	if (res) {
+		ast_log(LOG_WARNING, "Unable to get parameters of %s: %s\n", ast_channel_name(chan), strerror(errno));
+		return NULL;
+	}
+	if (!(dahdip.sigtype & __DAHDI_SIG_FXO)) {
+		ast_log(LOG_WARNING, "%s is not FXO signalled\n", ast_channel_name(chan));
+		return NULL;
+	}
+
+	pvt = ast_channel_tech_pvt(chan);
+	if (!dahdi_analog_lib_handles(pvt->sig, 0, 0)) {
+		ast_log(LOG_WARNING, "Channel signalling is not analog");
+		return NULL;
+	}
+
+	return pvt;
+}
+
+static int polarity_read(struct ast_channel *chan, const char *cmd, char *data, char *buffer, size_t buflen)
+{
+	struct dahdi_pvt *pvt;
+
+	pvt = fxo_pvt(chan);
+	if (!pvt) {
+		return -1;
+	}
+
+	snprintf(buffer, buflen, "%d", pvt->polarity);
+
+	return 0;
+}
+
+static int polarity_write(struct ast_channel *chan, const char *cmd, char *data, const char *value)
+{
+	struct dahdi_pvt *pvt;
+	int polarity;
+
+	pvt = fxo_pvt(chan);
+	if (!pvt) {
+		return -1;
+	}
+
+	if (!strcasecmp(value, "idle")) {
+		polarity = POLARITY_IDLE;
+	} else if (!strcasecmp(value, "reverse")) {
+		polarity = POLARITY_REV;
+	} else {
+		polarity = atoi(value);
+	}
+
+	if (polarity != POLARITY_IDLE && polarity != POLARITY_REV) {
+		ast_log(LOG_WARNING, "Invalid polarity: '%s'\n", value);
+		return -1;
+	}
+
+	my_set_polarity(pvt, polarity);
+	return 0;
+}
+
+static struct ast_custom_function polarity_function = {
+	.name = "POLARITY",
+	.write = polarity_write,
+	.read = polarity_read,
+};
+
 static int my_start(void *pvt)
 {
 	struct dahdi_pvt *p = pvt;
@@ -17615,6 +17724,8 @@ static int __unload_module(void)
 	ast_unregister_application(dahdi_accept_r2_call_app);
 #endif
 
+	ast_custom_function_unregister(&polarity_function);
+
 	ast_cli_unregister_multiple(dahdi_cli, ARRAY_LEN(dahdi_cli));
 	ast_manager_unregister("DAHDIDialOffhook");
 	ast_manager_unregister("DAHDIHangup");
@@ -19803,6 +19914,8 @@ static int load_module(void)
 	ast_register_application_xml(dahdi_accept_r2_call_app, dahdi_accept_r2_call_exec);
 #endif
 
+	ast_custom_function_register(&polarity_function);
+
 	ast_cli_register_multiple(dahdi_cli, ARRAY_LEN(dahdi_cli));
 	memset(round_robin, 0, sizeof(round_robin));
 	ast_manager_register_xml("DAHDITransfer", 0, action_transfer);

doc/CHANGES-staging/chan_dahdi_polarity.txt

@@ -0,0 +1,5 @@
+Subject: chan_dahdi
+
+A POLARITY function is now available that allows
+getting or setting the polarity on a channel
+from the dialplan.