feature/logtail: pull logtail + netlog out to modular features

Removes 434 KB from the minimal Linux binary, or ~3%.

Primarily this comes from not linking in the zstd encoding code.

Fixes #17323

Change-Id: I0a90de307dfa1ad7422db7aa8b1b46c782bfaaf7
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

wgengine/netlog/netlog.go

@@ -1,6 +1,8 @@
 // Copyright (c) Tailscale Inc & AUTHORS
 // SPDX-License-Identifier: BSD-3-Clause
 
+//go:build !ts_omit_netlog && !ts_omit_logtail
+
 // Package netlog provides a logger that monitors a TUN device and
 // periodically records any traffic into a log stream.
 package netlog

wgengine/netlog/netlog_omit.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build ts_omit_netlog || ts_omit_logtail
+
+package netlog
+
+type Logger struct{}
+
+func (*Logger) Startup(...any) error { return nil }
+func (*Logger) Running() bool        { return false }
+func (*Logger) Shutdown(any) error   { return nil }
+func (*Logger) ReconfigRoutes(any)   {}

wgengine/userspace.go

@@ -962,7 +962,7 @@ func (e *userspaceEngine) Reconfig(cfg *wgcfg.Config, routerCfg *router.Config,
 	netLogIDsWasValid := !oldLogIDs.NodeID.IsZero() && !oldLogIDs.DomainID.IsZero()
 	netLogIDsChanged := netLogIDsNowValid && netLogIDsWasValid && newLogIDs != oldLogIDs
 	netLogRunning := netLogIDsNowValid && !routerCfg.Equal(&router.Config{})
-	if envknob.NoLogsNoSupport() {
+	if !buildfeatures.HasNetLog || envknob.NoLogsNoSupport() {
 		netLogRunning = false
 	}
 
@@ -1017,7 +1017,7 @@ func (e *userspaceEngine) Reconfig(cfg *wgcfg.Config, routerCfg *router.Config,
 
 	// Shutdown the network logger because the IDs changed.
 	// Let it be started back up by subsequent logic.
-	if netLogIDsChanged && e.networkLogger.Running() {
+	if buildfeatures.HasNetLog && netLogIDsChanged && e.networkLogger.Running() {
 		e.logf("wgengine: Reconfig: shutting down network logger")
 		ctx, cancel := context.WithTimeout(context.Background(), networkLoggerUploadTimeout)
 		defer cancel()
@@ -1028,7 +1028,7 @@ func (e *userspaceEngine) Reconfig(cfg *wgcfg.Config, routerCfg *router.Config,
 
 	// Startup the network logger.
 	// Do this before configuring the router so that we capture initial packets.
-	if netLogRunning && !e.networkLogger.Running() {
+	if buildfeatures.HasNetLog && netLogRunning && !e.networkLogger.Running() {
 		nid := cfg.NetworkLogging.NodeID
 		tid := cfg.NetworkLogging.DomainID
 		logExitFlowEnabled := cfg.NetworkLogging.LogExitFlowEnabled