device: introduce generic function to inherit MTU from parent

Introduce a generic function to set a MTU based on parent's one. Also
define a device-specific @mtu_parent_delta value that specifies the
difference from parent MTU that should be set by default. For VLAN it
is zero but other interface types (for example MACsec) require a
positive value due to encapsulation overhead.

4 files changed, 36 insertions, 21 deletions

diff --git a/src/devices/nm-device-private.h b/src/devices/nm-device-private.h
index 4c38fa7a2a..b4bc6a1bfc 100644
--- a/src/devices/nm-device-private.h
+++ b/src/devices/nm-device-private.h
@@ -168,6 +168,9 @@ guint32 nm_device_get_configured_mtu_from_connection (NMDevice *device,
 
 guint32 nm_device_get_configured_mtu_for_wired (NMDevice *self, NMDeviceMtuSource *out_source);
 
+guint32 nm_device_get_configured_mtu_wired_parent (NMDevice *self,
+                                                   NMDeviceMtuSource *out_source);
+
 void nm_device_commit_mtu (NMDevice *self);
 
 /*****************************************************************************/
diff --git a/src/devices/nm-device-vlan.c b/src/devices/nm-device-vlan.c
index 02262b21d6..b6efeb81a5 100644
--- a/src/devices/nm-device-vlan.c
+++ b/src/devices/nm-device-vlan.c
@@ -502,26 +502,6 @@ act_stage1_prepare (NMDevice *device, NMDeviceStateReason *out_failure_reason)
 	return NM_ACT_STAGE_RETURN_SUCCESS;
 }
 
-static guint32
-get_configured_mtu (NMDevice *self, NMDeviceMtuSource *out_source)
-{
-	guint32 mtu = 0;
-	int ifindex;
-
-	mtu = nm_device_get_configured_mtu_for_wired (self, out_source);
-	if (*out_source != NM_DEVICE_MTU_SOURCE_NONE)
-		return mtu;
-
-	/* Inherit the MTU from parent device, if any */
-	ifindex = nm_device_parent_get_ifindex (self);
-	if (ifindex > 0) {
-		mtu = nm_platform_link_get_mtu (nm_device_get_platform (NM_DEVICE (self)), ifindex);
-		*out_source = NM_DEVICE_MTU_SOURCE_PARENT;
-	}
-
-	return mtu;
-}
-
 /*****************************************************************************/
 
 static void
@@ -577,6 +557,7 @@ nm_device_vlan_class_init (NMDeviceVlanClass *klass)
 	device_class->connection_type_supported = NM_SETTING_VLAN_SETTING_NAME;
 	device_class->connection_type_check_compatible = NM_SETTING_VLAN_SETTING_NAME;
 	device_class->link_types = NM_DEVICE_DEFINE_LINK_TYPES (NM_LINK_TYPE_VLAN);
+	device_class->mtu_parent_delta = 0; /* VLANs can have the same MTU of parent */
 
 	device_class->create_and_realize = create_and_realize;
 	device_class->link_changed = link_changed;
@@ -584,7 +565,7 @@ nm_device_vlan_class_init (NMDeviceVlanClass *klass)
 	device_class->get_generic_capabilities = get_generic_capabilities;
 	device_class->act_stage1_prepare_set_hwaddr_ethernet = TRUE;
 	device_class->act_stage1_prepare = act_stage1_prepare;
-	device_class->get_configured_mtu = get_configured_mtu;
+	device_class->get_configured_mtu = nm_device_get_configured_mtu_wired_parent;
 	device_class->is_available = is_available;
 	device_class->parent_changed_notify = parent_changed_notify;
 
diff --git a/src/devices/nm-device.c b/src/devices/nm-device.c
index 440a94c238..b6a00df645 100644
--- a/src/devices/nm-device.c
+++ b/src/devices/nm-device.c
@@ -9324,6 +9324,33 @@ nm_device_get_configured_mtu_for_wired (NMDevice *self, NMDeviceMtuSource *out_s
 	                                                     out_source);
 }
 
+guint32
+nm_device_get_configured_mtu_wired_parent (NMDevice *self,
+                                           NMDeviceMtuSource *out_source)
+{
+	guint32 mtu = 0;
+	int ifindex;
+
+	mtu = nm_device_get_configured_mtu_for_wired (self, out_source);
+	if (*out_source != NM_DEVICE_MTU_SOURCE_NONE) {
+		nm_assert (mtu > 0);
+		return mtu;
+	}
+
+	/* Inherit the MTU from parent device, if any */
+	ifindex = nm_device_parent_get_ifindex (self);
+	if (ifindex > 0) {
+		mtu = nm_platform_link_get_mtu (nm_device_get_platform (self), ifindex);
+		if (mtu >= NM_DEVICE_GET_CLASS (self)->mtu_parent_delta) {
+			mtu -= NM_DEVICE_GET_CLASS (self)->mtu_parent_delta;
+			*out_source = NM_DEVICE_MTU_SOURCE_PARENT;
+		} else
+			mtu = 0;
+	}
+
+	return mtu;
+}
+
 /*****************************************************************************/
 
 static void
diff --git a/src/devices/nm-device.h b/src/devices/nm-device.h
index df8777b720..40d9676d2d 100644
--- a/src/devices/nm-device.h
+++ b/src/devices/nm-device.h
@@ -225,6 +225,10 @@ typedef struct _NMDeviceClass {
 
 	const NMLinkType *link_types;
 
+	/* if the device MTU is set based on parent's one, this specifies
+	 * a delta in the MTU allowed value due the encapsulation overhead */
+	guint16 mtu_parent_delta;
+
 	/* Whether the device type is a master-type. This depends purely on the
 	 * type (NMDeviceClass), not the actual device instance. */
 	bool is_master:1;