wwan: Do not change initial bearer config and properly clear unused d…

…efault bearers

This commit addresses two issues related to cellular connectivity.

First, make sure that there are no bearers left from previous
connection attempts before starting a new connection, Otherwise, we may get
"interface-in-use-config-match" error from ModemManager.

Second, we should not change the initial EPS bearer settings and assume that
the same APN should be used for both the initial and the default bearer.
This is not always the case and the modem registration may fail when we
apply the same APN. However, we might want to make this user configurable
through EVE API and the controller.

Some background for understanding: LTE connection consists of two IP bearers,
the initial EPS bearer and the default bearer. Device must first establish
the initial bearer (which shows as transition from the "searching" to "registered"
state) and then it connects to a default bearer (transition from "registered" to
"connected"). Both bearers require PDP context settings (APN, ip-type, potentially
username/password, etc.).
Settings for the initial bearer are typically provided by the SIM card while
settings for the default bearer are user-configured.

It is not necessarily the case that the APNs for the initial and the default bearers
are the same. We used to make that assumption but this has led to cases where modem
was failing registration because the APN for the initial bearer was wrong. It is
better to let the SIM card provide the PDP context setting for the initial EPS bearer.
Furthermore, once these settings are changed, there is no straightforward method to
revert back to the SIM-provided configuration; for more details, see the discussion here:
https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/issues/1490#note_2628804

Users may only need to override SIM-provided settings in rather rare cases: either when
the SIM card has incorrect configuration (we have seen this only once) or when the initial
EPS bearer requires username/password authentication (also uncommon). Despite the rarity
of these cases, these settings should be user-configurable. We will do this later
(requires EVE API and controller changes).
Please note, that the same enhancement was recently implemented in NetworkManager
(used by Ubuntu and other major Linux distributions):
https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/1915

Signed-off-by: Milan Lenco <milan@zededa.com>
(cherry picked from commit a018521)

pkg/wwan/mmagent/mmdbus/client.go

@@ -669,6 +669,7 @@ func (c *Client) getModemStatus(modemObj dbus.BusObject) (
 	_ = getDBusProperty(c, modemObj, ModemPropertyBearers, &bearers)
 	for _, bearerPath := range bearers {
 		if !bearerPath.IsValid() {
+			c.log.Warnf("Bearer with an invalid dbus path: %s, skipping", bearerPath)
 			continue
 		}
 		bearerPaths = append(bearerPaths, string(bearerPath))
@@ -905,6 +906,7 @@ func (c *Client) getModemMetrics(
 	_ = getDBusProperty(c, modemObj, ModemPropertyBearers, &bearers)
 	for _, bearerPath := range bearers {
 		if !bearerPath.IsValid() {
+			c.log.Warnf("Bearer with an invalid dbus path: %s, skipping", bearerPath)
 			continue
 		}
 		bearerObj := c.conn.Object(MMInterface, bearerPath)
@@ -1208,6 +1210,8 @@ func (c *Client) Connect(
 			primarySIM = uint32(args.SIMSlot)
 			err := c.callDBusMethod(modemObj, ModemMethodSetPrimarySimSlot, nil, primarySIM)
 			if err != nil {
+				err = fmt.Errorf("failed to set SIM slot %d as primary for modem %s: %v",
+					primarySIM, modemPath, err)
 				return types.WwanIPSettings{}, err
 			}
 			err = c.waitForModemState(
@@ -1223,8 +1227,19 @@ func (c *Client) Connect(
 	// TODO: Not sure how to apply PreferredPLMNs with ModemManager.
 	err := c.setPreferredRATs(modemObj, args.PreferredRATs)
 	if err != nil {
+		err = fmt.Errorf("failed to set preferred RATs %v for modem %s: %v",
+			args.PreferredRATs, modemPath, err)
 		return types.WwanIPSettings{}, err
 	}
+	// Make sure that there are no previously created bearers still hanging
+	// around. Otherwise, we may get "interface-in-use-config-match" error
+	// from ModemManager.
+	err = c.deleteBearers(modemObj)
+	if err != nil {
+		// Just log as warning and continue with the connection attempt.
+		c.log.Warn(err)
+		err = nil
+	}
 	// Prepare connection settings.
 	connProps := make(map[string]interface{})
 	connProps["apn"] = args.APN
@@ -1252,42 +1267,63 @@ func (c *Client) Connect(
 	if err == nil {
 		return ipSettings, nil
 	}
-	origErr := err
-	// Try to fix failing connection attempt.
-	// First check if modem can even register.
-	changed, err := c.reconfigureEpsBearerIfNotRegistered(modemObj, connProps)
-	if changed && err == nil {
-		// Retry connection attempt with the same parameters applied also for the initial
-		// EPS bearer.
-		ipSettings, err = c.runSimpleConnect(modemObj, connProps)
-		if err == nil {
-			return ipSettings, nil
-		}
+	origErr := fmt.Errorf("failed to connect modem %s to APN %s: %v",
+		modemPath, args.APN, err)
+	// TODO: Allow the user to configure IP-type and PDP context for the initial EPS bearer.
+	// For now, we will be retrying connection attempts using all three IP types:
+	// ipv4, ipv6, ipv4v6. However, we will not be modifying the PDP context parameters
+	// for the initial EPS bearer until user is able to configure them.
+	//
+	// Some background for understanding: LTE connection consists of two IP bearers,
+	// the initial EPS bearer and the default EPS bearer. Device must first
+	// establish the initial bearer (which shows as transition from the "searching" to
+	// "registered" state) and then it connects to a default bearer (transition from
+	// "registered" to "connected"). Both bearers require PDP context settings (APN,
+	// ip-type, potentially username/password, etc.).
+	// Settings for the initial bearer are typically provided by the SIM card while
+	// settings for the default bearer are user-configured.
+	//
+	// It is not necessarily the case that the APNs for the initial and default bearers
+	// are the same. We used to make that assumption but this has led to cases where modem
+	// was failing registration because the APN for the initial bearer was wrong. It is
+	// better to let the SIM card provide the PDP context setting for the initial EPS bearer.
+	// Furthermore, once these settings are changed, there is no straightforward method to
+	// revert back to the SIM-provided configuration; for more details, see the discussion here:
+	// https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/issues/1490#note_2628804
+	//
+	// Users may only need to override SIM-provided settings in rather rare cases: either when
+	// the SIM card has incorrect configuration (we have seen this only once) or when the initial
+	// EPS bearer requires username/password authentication (also uncommon). Despite the rarity
+	// of these cases, these settings should be user-configurable.
+	// Please note, that the same enhancement was recently implemented in NetworkManager
+	// (used by Ubuntu and other major Linux distributions):
+	// https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/1915
+	err = c.deleteBearers(modemObj)
+	if err != nil {
+		// Just log as warning and continue with the next connection attempt for different
+		// ip-type.
+		c.log.Warn(err)
+		err = nil
 	}
-	// Next try IPv4 and IPv6 dual-stack.
+	// Try with dual-stack ip-type instead of IPv4 only.
 	connProps["ip-type"] = uint32(BearerIPFamilyIPv4v6)
-	_, err = c.reconfigureEpsBearerIfNotRegistered(modemObj, connProps)
+	ipSettings, err = c.runSimpleConnect(modemObj, connProps)
 	if err == nil {
-		ipSettings, err = c.runSimpleConnect(modemObj, connProps)
-		if err == nil {
-			return ipSettings, nil
-		}
+		return ipSettings, nil
+	}
+	err = c.deleteBearers(modemObj)
+	if err != nil {
+		// Just log as warning and continue with the next connection attempt for different
+		// ip-type.
+		c.log.Warn(err)
+		err = nil
 	}
 	// Make the final attempt with IPv6 only.
-	// This should be covered by IPv4v6 (network may return IPv6-only config
-	// in that case), but we make this attempt still just in case.
 	connProps["ip-type"] = uint32(BearerIPFamilyIPv6)
-	_, err = c.reconfigureEpsBearerIfNotRegistered(modemObj, connProps)
+	ipSettings, err = c.runSimpleConnect(modemObj, connProps)
 	if err == nil {
-		ipSettings, err = c.runSimpleConnect(modemObj, connProps)
-		if err == nil {
-			return ipSettings, nil
-		}
+		return ipSettings, nil
 	}
-	// Revert back the modem profile back to the preferred IPv4-only mode.
-	connProps["ip-type"] = uint32(BearerIPFamilyIPv4)
-	_, _ = c.reconfigureEpsBearerIfNotRegistered(modemObj, connProps)
-	// Return error from the first connection attempt (with IPv4-only).
 	return ipSettings, origErr
 }
 
@@ -1348,33 +1384,6 @@ func (c *Client) runSimpleConnect(modemObj dbus.BusObject,
 	return ipSettings, err
 }
 
-func (c *Client) reconfigureEpsBearerIfNotRegistered(modemObj dbus.BusObject,
-	newSettings map[string]interface{}) (changedConfig bool, err error) {
-	var modemState int32
-	_ = getDBusProperty(c, modemObj, ModemPropertyState, &modemState)
-	if modemState >= ModemStateRegistered {
-		return false, nil
-	}
-	var currentSettings map[string]dbus.Variant
-	_ = getDBusProperty(c, modemObj, Modem3GPPPropertyInitialEpsBearer, &currentSettings)
-	maskedPasswd := interface{}("***")
-	maskedVariantPasswd := dbus.MakeVariant(maskedPasswd)
-	c.log.Warnf("Modem %s is failing to register, "+
-		"trying to apply settings %+v for the initial EPS bearer (previously: %+v)",
-		modemObj.Path(), maskPassword(newSettings, maskedPasswd),
-		maskPassword(currentSettings, maskedVariantPasswd))
-	err = c.callDBusMethod(modemObj, Modem3GPPMethodSetInitialEpsBearer, nil, newSettings)
-	if err != nil {
-		err = fmt.Errorf(
-			"failed to change initial EPS bearer settings for modem %s: %w",
-			modemObj.Path(), err)
-		c.log.Error(err)
-		return false, err
-	}
-	return true, c.waitForModemState(
-		modemObj, ModemStateRegistered, changeInitEPSBearerTimeout)
-}
-
 // maskPassword creates a copy of the original map with the "password" key's value masked
 func maskPassword[Type any](data map[string]Type, maskWith Type) map[string]Type {
 	maskedData := make(map[string]Type)
@@ -1535,8 +1544,33 @@ func (c *Client) Disconnect(modemPath string) error {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
 	modemObj := c.conn.Object(MMInterface, dbus.ObjectPath(modemPath))
-	anyBearer := dbus.ObjectPath("/")
-	return c.callDBusMethod(modemObj, SimpleMethodDisconnect, nil, anyBearer)
+	return c.deleteBearers(modemObj)
+}
+
+// Delete all bearers which are associated with the given modem, except for
+// the initial EPS bearer, which stays connected.
+// This is used to disconnect the modem and to clean any bearers hanging
+// after a previously failed connection request.
+func (c *Client) deleteBearers(modemObj dbus.BusObject) error {
+	var bearers []dbus.ObjectPath
+	// This list does not include the initial EPS bearer details.
+	err := getDBusProperty(c, modemObj, ModemPropertyBearers, &bearers)
+	if err != nil {
+		return err
+	}
+	for _, bearerPath := range bearers {
+		if !bearerPath.IsValid() {
+			c.log.Warnf("Bearer with an invalid dbus path: %s, skipping", bearerPath)
+			continue
+		}
+		// If the bearer is currently active and providing packet data server, it will be
+		// disconnected and that packet data service will terminate.
+		err = c.callDBusMethod(modemObj, ModemMethodDeleteBearer, nil, bearerPath)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
 }
 
 // ScanVisibleProviders runs a fairly long operation (takes around 1 minute!)

pkg/wwan/mmagent/mmdbus/mmapi.go

@@ -31,6 +31,7 @@ const (
 	ModemMethodSetPowerState       = ModemInterface + ".SetPowerState"
 	ModemMethodSetPrimarySimSlot   = ModemInterface + ".SetPrimarySimSlot"
 	ModemMethodSetCurrentModes     = ModemInterface + ".SetCurrentModes"
+	ModemMethodDeleteBearer        = ModemInterface + ".DeleteBearer"
 	ModemPropertyModel             = ModemInterface + ".Model"
 	ModemPropertyRevision          = ModemInterface + ".Revision"
 	ModemPropertyManufacturer      = ModemInterface + ".Manufacturer"