all: cleanup unused code, part 2 (#10670)

And enable U1000 check in staticcheck.

Updates #cleanup

Signed-off-by: Andrew Lytvynov <awly@tailscale.com>

wgengine/magicsock/debugknobs.go

@@ -53,8 +53,12 @@ var (
 	// discovery on UDP connections between peers. Currently (2023-09-05)
 	// this only turns on the don't fragment bit for the magicsock UDP
 	// sockets.
+	//
+	//lint:ignore U1000 used on Linux/Darwin only
 	debugEnablePMTUD = envknob.RegisterOptBool("TS_DEBUG_ENABLE_PMTUD")
 	// debugPMTUD prints extra debugging about peer MTU path discovery.
+	//
+	//lint:ignore U1000 used on Linux/Darwin only
 	debugPMTUD = envknob.RegisterBool("TS_DEBUG_PMTUD")
 	// Hey you! Adding a new debugknob? Make sure to stub it out in the
 	// debugknobs_stubs.go file too.

wgengine/magicsock/magicsock.go

@@ -169,6 +169,8 @@ type Conn struct {
 	port atomic.Uint32
 
 	// peerMTUEnabled is whether path MTU discovery to peers is enabled.
+	//
+	//lint:ignore U1000 used on Linux/Darwin only
 	peerMTUEnabled atomic.Bool
 
 	// stats maintains per-connection counters.
@@ -2933,7 +2935,9 @@ var (
 	metricDERPHomeChange = clientmetric.NewCounter("derp_home_change")
 
 	// Disco packets received bpf read path
+	//lint:ignore U1000 used on Linux only
 	metricRecvDiscoPacketIPv4 = clientmetric.NewCounter("magicsock_disco_recv_bpf_ipv4")
+	//lint:ignore U1000 used on Linux only
 	metricRecvDiscoPacketIPv6 = clientmetric.NewCounter("magicsock_disco_recv_bpf_ipv6")
 
 	// metricMaxPeerMTUProbed is the largest peer path MTU we successfully probed.

wgengine/magicsock/peermtu_stubs.go

@@ -5,31 +5,6 @@
 
 package magicsock
 
-import (
-	"errors"
-)
-
-// setDontFragment sets the don't fragment sockopt on the underlying connection
-// specified by network, which must be "udp4" or "udp6". See
-// https://datatracker.ietf.org/doc/html/rfc3542#section-11.2 for details on
-// IPv6 fragmentation.
-//
-// Return values:
-// - an error if peer MTU is not supported on this OS
-// - errNoActiveUDP if the underlying connection is not UDP
-// - otherwise, the result of setting the don't fragment bit
-func (c *Conn) setDontFragment(network string, enable bool) error {
-	return errors.New("peer path MTU discovery not supported on this OS")
-}
-
-// getDontFragment gets the don't fragment setting on the underlying connection
-// specified by network, which must be "udp4" or "udp6". Returns true if the
-// underlying connection is UDP and the don't fragment bit is set, otherwise
-// false.
-func (c *Conn) getDontFragment(network string) (bool, error) {
-	return false, nil
-}
-
 func (c *Conn) DontFragSetting() (bool, error) {
 	return false, nil
 }

wgengine/router/ifconfig_windows.go

@@ -9,7 +9,6 @@ import (
 	"errors"
 	"fmt"
 	"log"
-	"net"
 	"net/netip"
 	"slices"
 	"sort"
@@ -28,8 +27,6 @@ import (
 	"tailscale.com/wgengine/winnet"
 )
 
-var wintunLinkLocal = netip.MustParseAddr("fe80::99d0:ec2d:b2e7:536b")
-
 // monitorDefaultRoutes subscribes to route change events and updates
 // the Tailscale tunnel interface's MTU to match that of the
 // underlying default route.
@@ -470,21 +467,6 @@ func configureInterface(cfg *Config, tun *tun.NativeTun) (retErr error) {
 	return errAcc
 }
 
-// unwrapIP returns the shortest version of ip.
-func unwrapIP(ip net.IP) net.IP {
-	if ip4 := ip.To4(); ip4 != nil {
-		return ip4
-	}
-	return ip
-}
-
-func v4Mask(m net.IPMask) net.IPMask {
-	if len(m) == 16 {
-		return m[12:]
-	}
-	return m
-}
-
 func netCompare(a, b netip.Prefix) int {
 	aip, bip := a.Addr().Unmap(), b.Addr().Unmap()
 	v := aip.Compare(bip)

wgengine/router/router_test.go

@@ -11,6 +11,7 @@ import (
 	"tailscale.com/types/preftype"
 )
 
+//lint:ignore U1000 used in Windows/Linux tests only
 func mustCIDRs(ss ...string) []netip.Prefix {
 	var ret []netip.Prefix
 	for _, s := range ss {