feature/sdnotify: move util/systemd to a modular feature

Updates #12614

Change-Id: I08e714c83b455df7f538cc99cafe940db936b480
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/derper/depaware.txt

@@ -88,6 +88,7 @@ tailscale.com/cmd/derper dependencies: (generated by github.com/tailscale/depawa
         tailscale.com/drive                                          from tailscale.com/client/local+
         tailscale.com/envknob                                        from tailscale.com/client/local+
         tailscale.com/feature                                        from tailscale.com/tsweb+
+        tailscale.com/feature/buildfeatures                          from tailscale.com/feature
         tailscale.com/health                                         from tailscale.com/net/tlsdial+
         tailscale.com/hostinfo                                       from tailscale.com/net/netmon+
         tailscale.com/ipn                                            from tailscale.com/client/local

cmd/k8s-operator/depaware.txt

@@ -164,7 +164,6 @@ tailscale.com/cmd/k8s-operator dependencies: (generated by github.com/tailscale/
    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
-   L    github.com/mdlayher/sdnotify                                 from tailscale.com/util/systemd
    L 💣 github.com/mdlayher/socket                                   from github.com/mdlayher/netlink+
      💣 github.com/mitchellh/go-ps                                   from tailscale.com/safesocket
         github.com/modern-go/concurrent                              from github.com/json-iterator/go
@@ -957,7 +956,6 @@ tailscale.com/cmd/k8s-operator dependencies: (generated by github.com/tailscale/
         tailscale.com/util/syspolicy/rsop                            from tailscale.com/util/syspolicy+
         tailscale.com/util/syspolicy/setting                         from tailscale.com/util/syspolicy+
         tailscale.com/util/syspolicy/source                          from tailscale.com/util/syspolicy+
-        tailscale.com/util/systemd                                   from tailscale.com/control/controlclient+
         tailscale.com/util/testenv                                   from tailscale.com/control/controlclient+
         tailscale.com/util/truncate                                  from tailscale.com/logtail
         tailscale.com/util/usermetric                                from tailscale.com/health+

cmd/stund/depaware.txt

@@ -51,6 +51,7 @@ tailscale.com/cmd/stund dependencies: (generated by github.com/tailscale/depawar
         tailscale.com                                                from tailscale.com/version
         tailscale.com/envknob                                        from tailscale.com/tsweb+
         tailscale.com/feature                                        from tailscale.com/tsweb
+        tailscale.com/feature/buildfeatures                          from tailscale.com/feature
         tailscale.com/kube/kubetypes                                 from tailscale.com/envknob
         tailscale.com/metrics                                        from tailscale.com/net/stunserver+
         tailscale.com/net/netaddr                                    from tailscale.com/net/tsaddr

cmd/tailscaled/depaware-minbox.txt

@@ -33,7 +33,6 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
      💣 github.com/mdlayher/netlink                                  from github.com/google/nftables+
      💣 github.com/mdlayher/netlink/nlenc                            from github.com/jsimonetti/rtnetlink+
         github.com/mdlayher/netlink/nltest                           from github.com/google/nftables
-        github.com/mdlayher/sdnotify                                 from tailscale.com/util/systemd
      💣 github.com/mdlayher/socket                                   from github.com/mdlayher/netlink+
      💣 github.com/safchain/ethtool                                  from tailscale.com/net/netkernelconf
         github.com/tailscale/hujson                                  from tailscale.com/ipn/conffile
@@ -202,7 +201,6 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/util/syspolicy/pkey                            from tailscale.com/cmd/tailscaled+
         tailscale.com/util/syspolicy/policyclient                    from tailscale.com/cmd/tailscaled+
         tailscale.com/util/syspolicy/ptype                           from tailscale.com/ipn/ipnlocal+
-        tailscale.com/util/systemd                                   from tailscale.com/control/controlclient+
         tailscale.com/util/testenv                                   from tailscale.com/control/controlclient+
         tailscale.com/util/usermetric                                from tailscale.com/health+
         tailscale.com/util/vizerror                                  from tailscale.com/tailcfg+

cmd/tailscaled/depaware.txt

@@ -147,7 +147,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
    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
-   L    github.com/mdlayher/sdnotify                                 from tailscale.com/util/systemd
+   L    github.com/mdlayher/sdnotify                                 from tailscale.com/feature/sdnotify
    L 💣 github.com/mdlayher/socket                                   from github.com/mdlayher/netlink+
      💣 github.com/mitchellh/go-ps                                   from tailscale.com/safesocket
    L    github.com/pierrec/lz4/v4                                    from github.com/u-root/uio/uio
@@ -282,6 +282,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/feature/portlist                               from tailscale.com/feature/condregister
         tailscale.com/feature/portmapper                             from tailscale.com/feature/condregister/portmapper
         tailscale.com/feature/relayserver                            from tailscale.com/feature/condregister
+   L    tailscale.com/feature/sdnotify                               from tailscale.com/feature/condregister
         tailscale.com/feature/syspolicy                              from tailscale.com/feature/condregister+
         tailscale.com/feature/taildrop                               from tailscale.com/feature/condregister
    L    tailscale.com/feature/tap                                    from tailscale.com/feature/condregister
@@ -446,7 +447,6 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/util/syspolicy/rsop                            from tailscale.com/util/syspolicy+
         tailscale.com/util/syspolicy/setting                         from tailscale.com/util/syspolicy+
         tailscale.com/util/syspolicy/source                          from tailscale.com/util/syspolicy+
-        tailscale.com/util/systemd                                   from tailscale.com/control/controlclient+
         tailscale.com/util/testenv                                   from tailscale.com/ipn/ipnlocal+
         tailscale.com/util/truncate                                  from tailscale.com/logtail
         tailscale.com/util/usermetric                                from tailscale.com/health+

cmd/tsidp/depaware.txt

@@ -128,7 +128,6 @@ tailscale.com/cmd/tsidp dependencies: (generated by github.com/tailscale/depawar
    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
-   L    github.com/mdlayher/sdnotify                                 from tailscale.com/util/systemd
    L 💣 github.com/mdlayher/socket                                   from github.com/mdlayher/netlink+
      💣 github.com/mitchellh/go-ps                                   from tailscale.com/safesocket
    D    github.com/prometheus-community/pro-bing                     from tailscale.com/wgengine/netstack
@@ -387,7 +386,6 @@ tailscale.com/cmd/tsidp dependencies: (generated by github.com/tailscale/depawar
         tailscale.com/util/syspolicy/rsop                            from tailscale.com/ipn/localapi+
         tailscale.com/util/syspolicy/setting                         from tailscale.com/client/local+
         tailscale.com/util/syspolicy/source                          from tailscale.com/util/syspolicy+
-        tailscale.com/util/systemd                                   from tailscale.com/control/controlclient+
         tailscale.com/util/testenv                                   from tailscale.com/control/controlclient+
         tailscale.com/util/truncate                                  from tailscale.com/logtail
         tailscale.com/util/usermetric                                from tailscale.com/health+

control/controlclient/direct.go

@@ -29,6 +29,7 @@ import (
 	"go4.org/mem"
 	"tailscale.com/control/controlknobs"
 	"tailscale.com/envknob"
+	"tailscale.com/feature"
 	"tailscale.com/health"
 	"tailscale.com/hostinfo"
 	"tailscale.com/ipn/ipnstate"
@@ -57,7 +58,6 @@ import (
 	"tailscale.com/util/singleflight"
 	"tailscale.com/util/syspolicy/pkey"
 	"tailscale.com/util/syspolicy/policyclient"
-	"tailscale.com/util/systemd"
 	"tailscale.com/util/testenv"
 	"tailscale.com/util/zstdframe"
 )
@@ -543,7 +543,9 @@ func (c *Direct) doLogin(ctx context.Context, opt loginOpt) (mustRegen bool, new
 	} else {
 		if expired {
 			c.logf("Old key expired -> regen=true")
-			systemd.Status("key expired; run 'tailscale up' to authenticate")
+			if f, ok := feature.HookSystemdStatus.GetOk(); ok {
+				f("key expired; run 'tailscale up' to authenticate")
+			}
 			regen = true
 		}
 		if (opt.Flags & LoginInteractive) != 0 {

feature/buildfeatures/feature_sdnotify_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_sdnotify
+
+package buildfeatures
+
+// HasSDNotify is whether the binary was built with support for modular feature "systemd notification support".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_sdnotify" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasSDNotify = false

feature/buildfeatures/feature_sdnotify_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_sdnotify
+
+package buildfeatures
+
+// HasSDNotify is whether the binary was built with support for modular feature "systemd notification support".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_sdnotify" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasSDNotify = true

feature/condregister/maybe_sdnotify.go

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

feature/featuretags/featuretags.go

@@ -145,6 +145,10 @@ var Features = map[FeatureTag]FeatureMeta{
 		Desc: "Linux systemd-resolved integration",
 		Deps: []FeatureTag{"dbus"},
 	},
+	"sdnotify": {
+		Sym:  "SDNotify",
+		Desc: "systemd notification support",
+	},
 	"serve": {
 		Sym:  "Serve",
 		Desc: "Serve and Funnel support",

feature/sdnotify.go

@@ -0,0 +1,32 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package feature
+
+import (
+	"runtime"
+
+	"tailscale.com/feature/buildfeatures"
+)
+
+// HookSystemdReady sends a readiness to systemd. This will unblock service
+// dependents from starting.
+var HookSystemdReady Hook[func()]
+
+// HookSystemdStatus holds a func that will send a single line status update to
+// systemd so that information shows up in systemctl output.
+var HookSystemdStatus Hook[func(format string, args ...any)]
+
+// SystemdStatus sends a single line status update to systemd so that
+// information shows up in systemctl output.
+//
+// It does nothing on non-Linux systems or if the binary was built without
+// the sdnotify feature.
+func SystemdStatus(format string, args ...any) {
+	if runtime.GOOS != "linux" || !buildfeatures.HasSDNotify {
+		return
+	}
+	if f, ok := HookSystemdStatus.GetOk(); ok {
+		f(format, args...)
+	}
+}

feature/sdnotify/sdnotify.go

@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: BSD-3-Clause
 
 /*
-Package systemd contains a minimal wrapper around systemd-notify to enable
+Package sdnotify contains a minimal wrapper around systemd-notify to enable
 applications to signal readiness and status to systemd.
 
 This package will only have effect on Linux systems running Tailscale in a
@@ -10,4 +10,4 @@ systemd unit with the Type=notify flag set. On other operating systems (or
 when running in a Linux distro without being run from inside systemd) this
 package will become a no-op.
 */
-package systemd
+package sdnotify

feature/sdnotify/sdnotify_linux.go

@@ -3,7 +3,7 @@
 
 //go:build linux && !android
 
-package systemd
+package sdnotify
 
 import (
 	"errors"
@@ -12,8 +12,14 @@ import (
 	"sync"
 
 	"github.com/mdlayher/sdnotify"
+	"tailscale.com/feature"
 )
 
+func init() {
+	feature.HookSystemdReady.Set(ready)
+	feature.HookSystemdStatus.Set(status)
+}
+
 var getNotifyOnce struct {
 	sync.Once
 	v *sdnotify.Notifier
@@ -46,15 +52,15 @@ func notifier() *sdnotify.Notifier {
 	return getNotifyOnce.v
 }
 
-// Ready signals readiness to systemd. This will unblock service dependents from starting.
+// ready signals readiness to systemd. This will unblock service dependents from starting.
-func Ready() {
+func ready() {
 	err := notifier().Notify(sdnotify.Ready)
 	if err != nil {
 		readyOnce.logf("systemd: error notifying: %v", err)
 	}
 }
 
-// Status sends a single line status update to systemd so that information shows up
+// status sends a single line status update to systemd so that information shows up
 // in systemctl output. For example:
 //
 //	$ systemctl status tailscale
@@ -69,7 +75,7 @@ func Ready() {
 //	CPU: 2min 38.469s
 //	CGroup: /system.slice/tailscale.service
 //	└─26741 /nix/store/sv6cj4mw2jajm9xkbwj07k29dj30lh0n-tailscale-date.20200727/bin/tailscaled --port 41641
-func Status(format string, args ...any) {
+func status(format string, args ...any) {
 	err := notifier().Notify(sdnotify.Statusf(format, args...))
 	if err != nil {
 		statusOnce.logf("systemd: error notifying: %v", err)

ipn/ipnlocal/local.go

@@ -102,7 +102,6 @@ import (
 	"tailscale.com/util/syspolicy/pkey"
 	"tailscale.com/util/syspolicy/policyclient"
 	"tailscale.com/util/syspolicy/ptype"
-	"tailscale.com/util/systemd"
 	"tailscale.com/util/testenv"
 	"tailscale.com/util/usermetric"
 	"tailscale.com/version"
@@ -5488,7 +5487,7 @@ func (b *LocalBackend) enterStateLockedOnEntry(newState ipn.State, unlock unlock
 
 	switch newState {
 	case ipn.NeedsLogin:
-		systemd.Status("Needs login: %s", authURL)
+		feature.SystemdStatus("Needs login: %s", authURL)
 		// always block updates on NeedsLogin even if seamless renewal is enabled,
 		// to prevent calls to authReconfig from reconfiguring the engine when our
 		// key has expired and we're waiting to authenticate to use the new key.
@@ -5503,7 +5502,7 @@ func (b *LocalBackend) enterStateLockedOnEntry(newState ipn.State, unlock unlock
 		}
 
 		if newState == ipn.Stopped && authURL == "" {
-			systemd.Status("Stopped; run 'tailscale up' to log in")
+			feature.SystemdStatus("Stopped; run 'tailscale up' to log in")
 		}
 	case ipn.Starting, ipn.NeedsMachineAuth:
 		b.authReconfig()
@@ -5515,7 +5514,7 @@ func (b *LocalBackend) enterStateLockedOnEntry(newState ipn.State, unlock unlock
 		for _, p := range addrs.All() {
 			addrStrs = append(addrStrs, p.Addr().String())
 		}
-		systemd.Status("Connected; %s; %s", activeLogin, strings.Join(addrStrs, " "))
+		feature.SystemdStatus("Connected; %s; %s", activeLogin, strings.Join(addrStrs, " "))
 	default:
 		b.logf("[unexpected] unknown newState %#v", newState)
 	}

ipn/ipnserver/server.go

@@ -23,6 +23,7 @@ import (
 
 	"tailscale.com/client/tailscale/apitype"
 	"tailscale.com/envknob"
+	"tailscale.com/feature"
 	"tailscale.com/ipn/ipnauth"
 	"tailscale.com/ipn/ipnlocal"
 	"tailscale.com/ipn/localapi"
@@ -32,7 +33,6 @@ import (
 	"tailscale.com/util/eventbus"
 	"tailscale.com/util/mak"
 	"tailscale.com/util/set"
-	"tailscale.com/util/systemd"
 	"tailscale.com/util/testenv"
 )
 
@@ -513,7 +513,9 @@ func (s *Server) Run(ctx context.Context, ln net.Listener) error {
 		ln.Close()
 	}()
 
-	systemd.Ready()
+	if ready, ok := feature.HookSystemdReady.GetOk(); ok {
+		ready()
+	}
 
 	hs := &http.Server{
 		Handler:     http.HandlerFunc(s.serveHTTP),

tsnet/depaware.txt

@@ -128,7 +128,6 @@ tailscale.com/tsnet dependencies: (generated by github.com/tailscale/depaware)
    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
-   L    github.com/mdlayher/sdnotify                                 from tailscale.com/util/systemd
   LA 💣 github.com/mdlayher/socket                                   from github.com/mdlayher/netlink+
  LDW 💣 github.com/mitchellh/go-ps                                   from tailscale.com/safesocket
   DI    github.com/prometheus-community/pro-bing                     from tailscale.com/wgengine/netstack
@@ -382,7 +381,6 @@ tailscale.com/tsnet dependencies: (generated by github.com/tailscale/depaware)
         tailscale.com/util/syspolicy/rsop                            from tailscale.com/ipn/localapi+
         tailscale.com/util/syspolicy/setting                         from tailscale.com/client/local+
         tailscale.com/util/syspolicy/source                          from tailscale.com/util/syspolicy+
-        tailscale.com/util/systemd                                   from tailscale.com/control/controlclient+
         tailscale.com/util/testenv                                   from tailscale.com/control/controlclient+
         tailscale.com/util/truncate                                  from tailscale.com/logtail
         tailscale.com/util/usermetric                                from tailscale.com/health+

util/systemd/systemd_nonlinux.go

@@ -1,9 +0,0 @@
-// Copyright (c) Tailscale Inc & AUTHORS
-// SPDX-License-Identifier: BSD-3-Clause
-
-//go:build !linux || android
-
-package systemd
-
-func Ready()                {}
-func Status(string, ...any) {}