iproute2: address: make Exact idempotent

Idempotence against address not available for Exact is not a bad idea if
we look at the name of that func

This should accomodate the race condition where keepalived will remove
vips should the primary address used for vrrp comms is removed, causing
later addr del to fail with "cannot assign requested address"

pkg/util/iproute2/address.go

@@ -16,6 +16,7 @@ package iproute2
 
 import (
 	"net"
+	"syscall"
 
 	"github.com/vishvananda/netlink"
 )
@@ -25,12 +26,17 @@ type Address struct {
 
 	addrBad bool
 	addrs   []*netlink.Addr
+
+	testcb func()
 }
 
+func nop() {}
+
 func NewAddress(ifname string, addresses ...string) *Address {
 	l := NewLink(ifname)
 	r := &Address{
-		Link: l,
+		Link:   l,
+		testcb: nop,
 	}
 
 	addrs := make([]*netlink.Addr, len(addresses))
@@ -76,6 +82,7 @@ func (address *Address) Exact() *Address {
 	if err != nil {
 		address.addErr(err, "Exact: AddrList")
 	}
+	address.testcb()
 	for _, oldAddr := range oldAddrs {
 		del := true
 		for _, addr := range address.addrs {
@@ -87,6 +94,13 @@ func (address *Address) Exact() *Address {
 		if del {
 			err := netlink.AddrDel(link, &oldAddr)
 			if err != nil {
+				if errno, ok := err.(syscall.Errno); ok {
+					switch errno {
+					case syscall.EADDRNOTAVAIL:
+						// "cannot assign requested address"
+						continue
+					}
+				}
 				address.addErr(err, "Exact: AddrDel %s", oldAddr)
 			}
 		}

pkg/util/iproute2/address_test.go

@@ -19,24 +19,24 @@ import (
 )
 
 func TestAddress(t *testing.T) {
-	ifname := genDummyName(t)
-	dum := addDummy(t, ifname)
-	defer delDummy(t, dum)
+	t.Run("exact some", func(t *testing.T) {
+		ifname := genDummyName(t)
+		dum := addDummy(t, ifname)
+		defer delDummy(t, dum)
 
-	emptyT := func(t *testing.T) {
-		l := NewAddress(ifname)
-		l.Exact()
-		if err := l.Err(); err != nil {
-			t.Fatalf("got err: %v", err)
-		}
-		if ipnets, err := l.List4(); err != nil {
-			t.Fatalf("list4 err: %v", err)
-		} else if len(ipnets) > 0 {
-			t.Fatalf("want empty, got %#v", ipnets)
+		emptyT := func(t *testing.T) {
+			l := NewAddress(ifname)
+			l.Exact()
+			if err := l.Err(); err != nil {
+				t.Fatalf("got err: %v", err)
+			}
+			if ipnets, err := l.List4(); err != nil {
+				t.Fatalf("list4 err: %v", err)
+			} else if len(ipnets) > 0 {
+				t.Fatalf("want empty, got %#v", ipnets)
+			}
 		}
-	}
 
-	t.Run("exact some", func(t *testing.T) {
 		want := "10.168.222.236/24"
 		l := NewAddress(ifname, want, "fe80::222:d5ff:fe9e:28d1/64")
 		l.Exact()
@@ -54,6 +54,35 @@ func TestAddress(t *testing.T) {
 		t.Run("empty empty", emptyT)
 	})
 
+	t.Run("exact indempotent", func(t *testing.T) {
+		ifname := genDummyName(t)
+		dum := addDummy(t, ifname)
+		defer delDummy(t, dum)
+
+		surprise := "10.127.190.240/32"
+		{
+			l := NewAddress(ifname, "10.127.190.217/24", surprise)
+			l.Exact()
+			if err := l.Err(); err != nil {
+				t.Fatalf("got err: %v", err)
+			}
+		}
+		{
+			l := NewAddress(ifname)
+			l.testcb = func() {
+				if err := NewAddress(ifname, surprise).Del().Err(); err != nil {
+					t.Fatalf("sneak failed: %v", err)
+				}
+			}
+			if addrs, _ := l.List4(); len(addrs) == 0 {
+				t.Fatalf("expect at least 1 v4 addr")
+			}
+			l.Exact()
+			if err := l.Err(); err != nil {
+				t.Fatalf("got err: %v", err)
+			}
+		}
+	})
 }
 
 func TestAddress_nopriv(t *testing.T) {