plugins: meta: portmap: Implement a teardown() fast path

Just attempt to delete the known rules referring to the custom chain,
then flush and delete it. If the latter succeeds, no referencing rules
are left and the job is done.

If the final flush'n'delete fails, fall back to the referencing rule
search which is slow with large rulesets.

Signed-off-by: Phil Sutter <psutter@redhat.com>

plugins/meta/portmap/chain.go

@@ -67,13 +67,27 @@ func (c *chain) setup(ipt *iptables.IPTables) error {
 // teardown idempotently deletes a chain. It will not error if the chain doesn't exist.
 // It will first delete all references to this chain in the entryChains.
 func (c *chain) teardown(ipt *iptables.IPTables) error {
-	// flush the chain
-	// This will succeed *and create the chain* if it does not exist.
-	// If the chain doesn't exist, the next checks will fail.
-	if err := utils.ClearChain(ipt, c.table, c.name); err != nil {
-		return err
+	// nothing to do if the custom chain doesn't exist to begin with
+	exists, err := ipt.ChainExists(c.table, c.name)
+	if err == nil && !exists {
+		return nil
+	}
+	// delete references created by setup()
+	for _, entryChain := range c.entryChains {
+		for _, rule := range c.entryRules {
+			r := []string{}
+			r = append(r, rule...)
+			r = append(r, "-j", c.name)
+
+			ipt.Delete(c.table, entryChain, r...)
+		}
+	}
+	// if chain deletion succeeds now, all references are gone
+	if err := ipt.ClearAndDeleteChain(c.table, c.name); err == nil {
+		return nil
 	}
 
+	// find references the hard way
 	for _, entryChain := range c.entryChains {
 		entryChainRules, err := ipt.List(c.table, entryChain)
 		if err != nil || len(entryChainRules) < 1 {
@@ -98,7 +112,7 @@ func (c *chain) teardown(ipt *iptables.IPTables) error {
 		}
 	}
 
-	return utils.DeleteChain(ipt, c.table, c.name)
+	return ipt.ClearAndDeleteChain(c.table, c.name)
 }
 
 // check the chain.