Re: [PATCH v2 net-next 1/8] net: bridge: vlan: notify switchdev only when something changed

On Tue, Feb 15, 2022 at 10:54:26AM +0200, Nikolay Aleksandrov wrote:

quoted

+/* return true if anything will change as a result of __vlan_add_flags,
+ * false otherwise
+ */
+static bool __vlan_flags_would_change(struct net_bridge_vlan *v, u16 flags)
+{
+	struct net_bridge_vlan_group *vg;
+	u16 old_flags = v->flags;
+	bool pvid_changed;
 
-	return ret || !!(old_flags ^ v->flags);
+	if (br_vlan_is_master(v))
+		vg = br_vlan_group(v->br);
+	else
+		vg = nbp_vlan_group(v->port);
+
+	if (flags & BRIDGE_VLAN_INFO_PVID)
+		pvid_changed = (vg->pvid == v->vid);
+	else
+		pvid_changed = (vg->pvid != v->vid);
+
+	return pvid_changed || !!(old_flags ^ v->flags);
 }

These two have to depend on each other, otherwise it's error-prone and
surely in the future someone will forget to update both.
How about add a "commit" argument to __vlan_add_flags and possibly rename
it to __vlan_update_flags, then add 2 small helpers like __vlan_update_flags_precommit
with commit == false and __vlan_update_flags_commit with commit == true.
Or some other naming, the point is to always use the same flow and checks
when updating the flags to make sure people don't forget.

You want to squash __vlan_flags_would_change() and __vlan_add_flags()
into a single function? But "would_change" returns bool, and "add"
returns void.

quoted

 
 static int __vlan_vid_add(struct net_device *dev, struct net_bridge *br,

@@ -672,9 +685,13 @@ static int br_vlan_add_existing(struct net_bridge *br,
 {
 	int err;
 
-	err = br_switchdev_port_vlan_add(br->dev, vlan->vid, flags, extack);
-	if (err && err != -EOPNOTSUPP)
-		return err;
+	*changed = __vlan_flags_would_change(vlan, flags);
+	if (*changed) {
+		err = br_switchdev_port_vlan_add(br->dev, vlan->vid, flags,
+						 extack);
+		if (err && err != -EOPNOTSUPP)
+			return err;
+	}

You should revert *changed to false in the error path below,
otherwise we will emit a notification without anything changed
if the br_vlan_is_brentry(vlan)) { } block errors out.

Ok.