o/ifacestate: add some comments and rename some functions to hopefully help reading

Author: andrewphelpsj

overlord/ifacestate/handlers.go

@@ -337,6 +337,9 @@ func (d delayedEffectsForSnaps) EnqueueFor(snapName affectedSnap, backend interf
 	d[snapName][backend] = append(d[snapName][backend], item)
 }
 
+// refreshAppSetConnections refreshes repository connections for appSet and, on
+// the setup-profiles do path, records undo data for persisted connection state
+// that reloadConnections changed or dropped.
 func (m *InterfaceManager) refreshAppSetConnections(task *state.Task, appSet *interfaces.SnapAppSet) ([]string, []string, error) {
 	snapInfo := appSet.Info()
 	snapName := appSet.InstanceName()
@@ -369,16 +372,16 @@ func (m *InterfaceManager) refreshAppSetConnections(task *state.Task, appSet *in
 		task.Logf("%s", snap.BadInterfacesSummary(snapInfo))
 	}
 
-	reloadedConns, changedConns, err := m.reloadConnections(snapName)
+	reloadedConns, changedOrDroppedConns, err := m.reloadConnections(snapName)
 	if err != nil {
 		return nil, nil, err
 	}
 
-	// if this task modified any connection states, we take a snapshot of the
-	// original connections so that we can restore them on the undo path, if
+	// if this task modified any connection states, take a snapshot of the
+	// original connections so that setup-profiles' undo can restore them, if
 	// needed
 	if task.Status() != state.UndoingStatus {
-		if err := snapshotChangedConnectionsForUndo(task, snapName, changedConns); err != nil {
+		if err := snapshotChangedConnectionsForUndo(task, snapName, changedOrDroppedConns); err != nil {
 			return nil, nil, err
 		}
 	}
@@ -706,6 +709,10 @@ func (m *InterfaceManager) undoSetupProfiles(task *state.Task, tomb *tomb.Tomb)
 	if err := snapstateFinishRestart(task, snapsup, finishOpts); err != nil {
 		return err
 	}
+
+	// restore any connection state snapshot saved by refreshAppSetConnections on
+	// the original setup-profiles do path before rebuilding profiles for the old
+	// revision
 	if err := restoreConnectionsForSetupProfiles(task); err != nil {
 		return err
 	}

overlord/ifacestate/helpers.go

@@ -444,8 +444,9 @@ func cloneConnState(connState *schema.ConnState) *schema.ConnState {
 	return &clone
 }
 
-// snapshotChangedConnectionsForUndo records original states for connections
-// changed by setup-profiles so undo can restore them, if needed.
+// snapshotChangedConnectionsForUndo records original states for persisted
+// connections that setup-profiles changed or dropped so undo can restore them,
+// if needed.
 func snapshotChangedConnectionsForUndo(task *state.Task, instanceName string, changedConns map[string]*schema.ConnState) error {
 	if len(changedConns) == 0 {
 		return nil
@@ -480,8 +481,8 @@ func snapshotChangedConnectionsForUndo(task *state.Task, instanceName string, ch
 	return nil
 }
 
-// restoreConnectionsForSetupProfiles restores connection states saved on a
-// setup-profiles task.
+// restoreConnectionsForSetupProfiles restores connection states saved by
+// snapshotChangedConnectionsForUndo on a setup-profiles task.
 func restoreConnectionsForSetupProfiles(task *state.Task) error {
 	var connectionSnapshot map[string]*schema.ConnState
 	err := task.Get("changed-connection-snapshot", &connectionSnapshot)
@@ -512,8 +513,12 @@ func restoreConnectionsForSetupProfiles(task *state.Task) error {
 // affecting a given snap.
 //
 // The return value is the list of reloaded connection IDs, plus the original
-// connection states whose persisted state was changed.
-func (m *InterfaceManager) reloadConnections(snapName string) (reloadedConnectionIDs []string, changedConns map[string]*schema.ConnState, err error) {
+// connection states whose persisted state was changed or dropped.
+func (m *InterfaceManager) reloadConnections(snapName string) (
+	reloadedConnectionIDs []string,
+	changedOrDroppedConns map[string]*schema.ConnState,
+	err error,
+) {
 	conns, err := getConns(m.state)
 	if err != nil {
 		return nil, nil, err
@@ -542,7 +547,7 @@ func (m *InterfaceManager) reloadConnections(snapName string) (reloadedConnectio
 	}
 
 	connStateChanged := false
-	changedConns = make(map[string]*schema.ConnState)
+	changedOrDroppedConns = make(map[string]*schema.ConnState)
 
 	var reloadedConnections []string
 ConnsLoop:
@@ -587,7 +592,7 @@ ConnsLoop:
 						continue ConnsLoop
 					}
 				}
-				changedConns[connId] = cloneConnState(connState)
+				changedOrDroppedConns[connId] = cloneConnState(connState)
 				delete(conns, connId)
 				connStateChanged = true
 			}
@@ -652,7 +657,7 @@ ConnsLoop:
 			reloadedConnections = append(reloadedConnections, connId)
 
 			if updateStaticAttrs {
-				changedConns[connId] = cloneConnState(connState)
+				changedOrDroppedConns[connId] = cloneConnState(connState)
 				connState.StaticPlugAttrs = staticPlugAttrs
 				connState.StaticSlotAttrs = staticSlotAttrs
 				connStateChanged = true
@@ -663,7 +668,7 @@ ConnsLoop:
 		setConns(m.state, conns)
 	}
 
-	return reloadedConnections, changedConns, nil
+	return reloadedConnections, changedOrDroppedConns, nil
 }
 
 // removeConnections disconnects all connections of the snap in the repo. It should only be used if the snap