Add noroaming config key and document USB tethering

Signed-off-by: Philippe De Swert <philippe.deswert@jollamobile.com>

docs/usb_moded-doc.txt

@@ -356,3 +356,22 @@ Usb-moded supports a diagnostic mode. This requires a special command line param
 One mode should be configured in /etc/usb-moded/diag and this will be automatically used.
 This is a feature to allow for "hidden" or non-standard modes that are only of use for 
 testing/QA.
+
+USB tethering
+-------------
+
+Usb_moded can set up USB tethering. In the sense that it can share the connection of your device to a second one.
+Most common use case would be using USB tethering from a phone to a laptop.
+
+When compiled with ofono and connman support you can make the most of this. ofono can be used to detect roaming status.
+Connman for getting dns settings and interface from the modem connection.
+However it works also without it. It can be configured so that it knows what the interfaces are and get the dns info 
+from /etc/resolv.conf.
+
+For this are the 
+
+#define NETWORK_NAT_INTERFACE_KEY       "nat_interface"
+#define NO_ROAMING_KEY                  "noroaming"
+
+Network options. nat_interface documents which interfaces the internet facing modem. noroaming when set to 1
+will prohibit enabling the modem interface in case you are roaming (this requires ofono). 

src/usb_moded-config.c

@@ -607,3 +607,7 @@ int check_android_section(void)
   return(ret);
 }
 
+int is_roaming_not_allowed(void)
+{
+  return(get_conf_int(NETWORK_ENTRY, NO_ROAMING_KEY));
+}

src/usb_moded-config.h

@@ -49,6 +49,7 @@
 #define NETWORK_INTERFACE_KEY		"interface"
 #define NETWORK_GATEWAY_KEY		"gateway"
 #define NETWORK_NAT_INTERFACE_KEY	"nat_interface"
+#define NO_ROAMING_KEY			"noroaming"
 #define ANDROID_ENTRY			"android"
 #define ANDROID_MANUFACTURER_KEY	"iManufacturer"
 #define ANDROID_VENDOR_ID_KEY		"idVendor"
@@ -89,5 +90,7 @@ const char * get_android_product_id(void);
 
 int check_android_section(void);
 
+int is_roaming_not_allowed(void);
+
 int conf_file_merge(void);
 int set_config_setting(const char *entry, const char *key, const char *value);

src/usb_moded-network.c

@@ -564,7 +564,11 @@ int usb_network_set_up_dhcpd(struct mode_list_elem *data)
 #ifdef OFONO
 	/* check if we are roaming or not */
 	if(get_roaming())
-		goto end;
+	{
+		/* get permission to use roaming */
+		if(is_roaming_not_allowed())
+			goto end;
+	}
 #endif /* OFONO */
 	ipforward = malloc(sizeof(struct ipforward_data));
 	memset(ipforward, 0, sizeof(struct ipforward_data));