feature/linkspeed: move cosmetic tstun netlink code out to modular feature

Part of making all netlink monitoring code optional.

Updates #17311 (how I got started down this path)
Updates #12614

Change-Id: Ic80d8a7a44dc261c4b8678b3c2241c3b3778370d
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/k8s-operator/depaware.txt

@@ -74,7 +74,6 @@ tailscale.com/cmd/k8s-operator dependencies: (generated by github.com/tailscale/
         github.com/mailru/easyjson/buffer                            from github.com/mailru/easyjson/jwriter
      💣 github.com/mailru/easyjson/jlexer                            from github.com/go-openapi/swag
         github.com/mailru/easyjson/jwriter                           from github.com/go-openapi/swag
-   L    github.com/mdlayher/genetlink                                from tailscale.com/net/tstun
    L 💣 github.com/mdlayher/netlink                                  from github.com/jsimonetti/rtnetlink+
    L 💣 github.com/mdlayher/netlink/nlenc                            from github.com/jsimonetti/rtnetlink+
    L 💣 github.com/mdlayher/socket                                   from github.com/mdlayher/netlink+
@@ -907,7 +906,7 @@ tailscale.com/cmd/k8s-operator dependencies: (generated by github.com/tailscale/
         golang.org/x/exp/constraints                                 from tailscale.com/tsweb/varz+
         golang.org/x/exp/maps                                        from sigs.k8s.io/controller-runtime/pkg/cache+
         golang.org/x/exp/slices                                      from tailscale.com/cmd/k8s-operator+
-        golang.org/x/net/bpf                                         from github.com/mdlayher/genetlink+
+        golang.org/x/net/bpf                                         from github.com/mdlayher/netlink+
         golang.org/x/net/dns/dnsmessage                              from tailscale.com/appc+
         golang.org/x/net/http/httpguts                               from golang.org/x/net/http2+
         golang.org/x/net/http/httpproxy                              from tailscale.com/net/tshttpproxy

cmd/tailscaled/depaware-min.txt

@@ -19,7 +19,6 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         github.com/klauspost/compress/internal/snapref               from github.com/klauspost/compress/zstd
         github.com/klauspost/compress/zstd                           from tailscale.com/util/zstdframe
         github.com/klauspost/compress/zstd/internal/xxhash           from github.com/klauspost/compress/zstd
-        github.com/mdlayher/genetlink                                from tailscale.com/net/tstun
      💣 github.com/mdlayher/netlink                                  from github.com/jsimonetti/rtnetlink+
      💣 github.com/mdlayher/netlink/nlenc                            from github.com/jsimonetti/rtnetlink+
      💣 github.com/mdlayher/socket                                   from github.com/mdlayher/netlink
@@ -204,7 +203,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         golang.org/x/crypto/salsa20/salsa                            from golang.org/x/crypto/nacl/box+
         golang.org/x/exp/constraints                                 from tailscale.com/util/set
         golang.org/x/exp/maps                                        from tailscale.com/ipn/store/mem
-        golang.org/x/net/bpf                                         from github.com/mdlayher/genetlink+
+        golang.org/x/net/bpf                                         from github.com/mdlayher/netlink+
         golang.org/x/net/dns/dnsmessage                              from tailscale.com/ipn/ipnlocal+
         golang.org/x/net/http/httpguts                               from tailscale.com/ipn/ipnlocal
         golang.org/x/net/icmp                                        from tailscale.com/net/ping

cmd/tailscaled/depaware-minbox.txt

@@ -25,7 +25,6 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         github.com/klauspost/compress/zstd/internal/xxhash           from github.com/klauspost/compress/zstd
         github.com/mattn/go-colorable                                from tailscale.com/cmd/tailscale/cli
         github.com/mattn/go-isatty                                   from github.com/mattn/go-colorable+
-        github.com/mdlayher/genetlink                                from tailscale.com/net/tstun
      💣 github.com/mdlayher/netlink                                  from github.com/jsimonetti/rtnetlink+
      💣 github.com/mdlayher/netlink/nlenc                            from github.com/jsimonetti/rtnetlink+
      💣 github.com/mdlayher/socket                                   from github.com/mdlayher/netlink
@@ -232,7 +231,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         golang.org/x/crypto/salsa20/salsa                            from golang.org/x/crypto/nacl/box+
         golang.org/x/exp/constraints                                 from tailscale.com/util/set
         golang.org/x/exp/maps                                        from tailscale.com/ipn/store/mem
-        golang.org/x/net/bpf                                         from github.com/mdlayher/genetlink+
+        golang.org/x/net/bpf                                         from github.com/mdlayher/netlink+
         golang.org/x/net/dns/dnsmessage                              from tailscale.com/cmd/tailscale/cli+
         golang.org/x/net/http/httpguts                               from tailscale.com/ipn/ipnlocal
         golang.org/x/net/icmp                                        from tailscale.com/net/ping

cmd/tailscaled/depaware.txt

@@ -143,7 +143,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         github.com/klauspost/compress/zstd/internal/xxhash           from github.com/klauspost/compress/zstd
         github.com/kortschak/wol                                     from tailscale.com/feature/wakeonlan
   LD    github.com/kr/fs                                             from github.com/pkg/sftp
-   L    github.com/mdlayher/genetlink                                from tailscale.com/net/tstun
+   L    github.com/mdlayher/genetlink                                from tailscale.com/feature/linkspeed
    L 💣 github.com/mdlayher/netlink                                  from github.com/google/nftables+
    L 💣 github.com/mdlayher/netlink/nlenc                            from github.com/jsimonetti/rtnetlink+
    L    github.com/mdlayher/netlink/nltest                           from github.com/google/nftables
@@ -285,6 +285,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/feature/debugportmapper                        from tailscale.com/feature/condregister
         tailscale.com/feature/doctor                                 from tailscale.com/feature/condregister
         tailscale.com/feature/drive                                  from tailscale.com/feature/condregister
+   L    tailscale.com/feature/linkspeed                              from tailscale.com/feature/condregister
    L    tailscale.com/feature/linuxdnsfight                          from tailscale.com/feature/condregister
         tailscale.com/feature/portlist                               from tailscale.com/feature/condregister
         tailscale.com/feature/portmapper                             from tailscale.com/feature/condregister/portmapper

cmd/tailscaled/deps_test.go

@@ -287,6 +287,7 @@ func TestMinTailscaledWithCLI(t *testing.T) {
 		BadDeps: map[string]string{
 			"golang.org/x/net/http2":        "unexpected x/net/http2 dep; tailscale/tailscale#17305",
 			"expvar":                        "unexpected expvar dep",
+			"github.com/mdlayher/genetlink": "unexpected genetlink dep",
 		},
 	}.Check(t)
 }

cmd/tsidp/depaware.txt

@@ -38,7 +38,6 @@ tailscale.com/cmd/tsidp dependencies: (generated by github.com/tailscale/depawar
         github.com/klauspost/compress/internal/snapref               from github.com/klauspost/compress/zstd
         github.com/klauspost/compress/zstd                           from tailscale.com/util/zstdframe
         github.com/klauspost/compress/zstd/internal/xxhash           from github.com/klauspost/compress/zstd
-   L    github.com/mdlayher/genetlink                                from tailscale.com/net/tstun
    L 💣 github.com/mdlayher/netlink                                  from github.com/jsimonetti/rtnetlink+
    L 💣 github.com/mdlayher/netlink/nlenc                            from github.com/jsimonetti/rtnetlink+
    L 💣 github.com/mdlayher/socket                                   from github.com/mdlayher/netlink+
@@ -335,7 +334,7 @@ tailscale.com/cmd/tsidp dependencies: (generated by github.com/tailscale/depawar
   LD    golang.org/x/crypto/ssh/internal/bcrypt_pbkdf                from golang.org/x/crypto/ssh
         golang.org/x/exp/constraints                                 from tailscale.com/tsweb/varz+
         golang.org/x/exp/maps                                        from tailscale.com/ipn/store/mem+
-        golang.org/x/net/bpf                                         from github.com/mdlayher/genetlink+
+        golang.org/x/net/bpf                                         from github.com/mdlayher/netlink+
         golang.org/x/net/dns/dnsmessage                              from tailscale.com/appc+
         golang.org/x/net/http/httpguts                               from tailscale.com/ipn/ipnlocal
         golang.org/x/net/http/httpproxy                              from tailscale.com/net/tshttpproxy

feature/buildfeatures/feature_linkspeed_disabled.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build ts_omit_linkspeed
+
+package buildfeatures
+
+// HasLinkSpeed is whether the binary was built with support for modular feature "Set link speed on TUN device for better OS integration (Linux only)".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_linkspeed" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasLinkSpeed = false

feature/buildfeatures/feature_linkspeed_enabled.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build !ts_omit_linkspeed
+
+package buildfeatures
+
+// HasLinkSpeed is whether the binary was built with support for modular feature "Set link speed on TUN device for better OS integration (Linux only)".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_linkspeed" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasLinkSpeed = true

feature/condregister/maybe_linkspeed.go

@@ -0,0 +1,8 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build linux && !android && !ts_omit_linkspeed
+
+package condregister
+
+import _ "tailscale.com/feature/linkspeed"

feature/featuretags/featuretags.go

@@ -161,6 +161,10 @@ var Features = map[FeatureTag]FeatureMeta{
 	"kube":          {Sym: "Kube", Desc: "Kubernetes integration"},
 	"lazywg":        {Sym: "LazyWG", Desc: "Lazy WireGuard configuration for memory-constrained devices with large netmaps"},
 	"linuxdnsfight": {Sym: "LinuxDNSFight", Desc: "Linux support for detecting DNS fights (inotify watching of /etc/resolv.conf)"},
+	"linkspeed": {
+		Sym:  "LinkSpeed",
+		Desc: "Set link speed on TUN device for better OS integration (Linux only)",
+	},
 	"listenrawdisco": {
 		Sym:  "ListenRawDisco",
 		Desc: "Use raw sockets for more robust disco (NAT traversal) message receiving (Linux only)",

feature/linkspeed/doc.go

@@ -0,0 +1,6 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Package linkspeed registers support for setting the TUN link speed on Linux,
+// to better integrate with system monitoring tools.
+package linkspeed

feature/linkspeed/linkspeed_linux.go

@@ -1,17 +1,22 @@
 // Copyright (c) Tailscale Inc & AUTHORS
 // SPDX-License-Identifier: BSD-3-Clause
 
-//go:build !android
+//go:build linux && !android
 
-package tstun
+package linkspeed
 
 import (
 	"github.com/mdlayher/genetlink"
 	"github.com/mdlayher/netlink"
 	"github.com/tailscale/wireguard-go/tun"
 	"golang.org/x/sys/unix"
+	"tailscale.com/net/tstun"
 )
 
+func init() {
+	tstun.HookSetLinkAttrs.Set(setLinkAttrs)
+}
+
 // setLinkSpeed sets the advertised link speed of the TUN interface.
 func setLinkSpeed(iface tun.Device, mbps int) error {
 	name, err := iface.Name()

net/tstun/linkattrs_notlinux.go

@@ -1,12 +0,0 @@
-// Copyright (c) Tailscale Inc & AUTHORS
-// SPDX-License-Identifier: BSD-3-Clause
-
-//go:build !linux || android
-
-package tstun
-
-import "github.com/tailscale/wireguard-go/tun"
-
-func setLinkAttrs(iface tun.Device) error {
-	return nil
-}

net/tstun/tun.go

@@ -18,12 +18,16 @@ import (
 
 	"github.com/tailscale/wireguard-go/tun"
 	"tailscale.com/feature"
+	"tailscale.com/feature/buildfeatures"
 	"tailscale.com/types/logger"
 )
 
-// CreateTAP is the hook set by feature/tap.
+// CreateTAP is the hook maybe set by feature/tap.
 var CreateTAP feature.Hook[func(logf logger.Logf, tapName, bridgeName string) (tun.Device, error)]
 
+// HookSetLinkAttrs is the hook maybe set by feature/linkspeed.
+var HookSetLinkAttrs feature.Hook[func(tun.Device) error]
+
 // modprobeTunHook is a Linux-specific hook to run "/sbin/modprobe tun".
 var modprobeTunHook feature.Hook[func() error]
 
@@ -78,9 +82,13 @@ func New(logf logger.Logf, tunName string) (tun.Device, string, error) {
 		dev.Close()
 		return nil, "", err
 	}
-	if err := setLinkAttrs(dev); err != nil {
+	if buildfeatures.HasLinkSpeed {
+		if f, ok := HookSetLinkAttrs.GetOk(); ok {
+			if err := f(dev); err != nil {
 				logf("setting link attributes: %v", err)
 			}
+		}
+	}
 	name, err := interfaceName(dev)
 	if err != nil {
 		dev.Close()

tsnet/depaware.txt

@@ -38,7 +38,6 @@ tailscale.com/tsnet dependencies: (generated by github.com/tailscale/depaware)
         github.com/klauspost/compress/internal/snapref               from github.com/klauspost/compress/zstd
         github.com/klauspost/compress/zstd                           from tailscale.com/util/zstdframe
         github.com/klauspost/compress/zstd/internal/xxhash           from github.com/klauspost/compress/zstd
-   L    github.com/mdlayher/genetlink                                from tailscale.com/net/tstun
    L 💣 github.com/mdlayher/netlink                                  from github.com/jsimonetti/rtnetlink+
    L 💣 github.com/mdlayher/netlink/nlenc                            from github.com/jsimonetti/rtnetlink+
   LA 💣 github.com/mdlayher/socket                                   from github.com/mdlayher/netlink+
@@ -328,7 +327,7 @@ tailscale.com/tsnet dependencies: (generated by github.com/tailscale/depaware)
   LD    golang.org/x/crypto/ssh/internal/bcrypt_pbkdf                from golang.org/x/crypto/ssh
         golang.org/x/exp/constraints                                 from tailscale.com/tsweb/varz+
         golang.org/x/exp/maps                                        from tailscale.com/ipn/store/mem+
-        golang.org/x/net/bpf                                         from github.com/mdlayher/genetlink+
+        golang.org/x/net/bpf                                         from github.com/mdlayher/netlink+
         golang.org/x/net/dns/dnsmessage                              from tailscale.com/appc+
         golang.org/x/net/http/httpguts                               from tailscale.com/ipn/ipnlocal
         golang.org/x/net/http/httpproxy                              from tailscale.com/net/tshttpproxy