cmd/tailscaled: allow setting env via linux cmdline for integration tests

Updates #13038

Change-Id: I51e016d0eb7c14647159706c08f017fdedd68e2a
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/tailscaled/tailscaled.go

@@ -35,6 +35,7 @@
 	"tailscale.com/control/controlclient"
 	"tailscale.com/drive/driveimpl"
 	"tailscale.com/envknob"
+	"tailscale.com/hostinfo"
 	"tailscale.com/ipn"
 	"tailscale.com/ipn/conffile"
 	"tailscale.com/ipn/ipnlocal"
@@ -154,6 +155,7 @@ func defaultPort() uint16 {
 func main() {
 	envknob.PanicIfAnyEnvCheckedInInit()
 	envknob.ApplyDiskConfig()
+	applyIntegrationTestEnvKnob()
 
 	printVersion := false
 	flag.IntVar(&args.verbose, "verbose", 0, "log verbosity level; 0 is default, 1 or higher are increasingly verbose")
@@ -895,3 +897,24 @@ func dieOnPipeReadErrorOfFD(fd int) {
 	f.Read(make([]byte, 1))
 	os.Exit(1)
 }
+
+// applyIntegrationTestEnvKnob applies the tailscaled.env=... environment
+// variables specified on the Linux kernel command line, if the VM is being
+// run in NATLab integration tests.
+//
+// They're specified as: tailscaled.env=FOO=bar tailscaled.env=BAR=baz
+func applyIntegrationTestEnvKnob() {
+	if runtime.GOOS != "linux" || !hostinfo.IsNATLabGuestVM() {
+		return
+	}
+	cmdLine, _ := os.ReadFile("/proc/cmdline")
+	for _, s := range strings.Fields(string(cmdLine)) {
+		suf, ok := strings.CutPrefix(s, "tailscaled.env=")
+		if !ok {
+			continue
+		}
+		if k, v, ok := strings.Cut(suf, "="); ok {
+			envknob.Setenv(k, v)
+		}
+	}
+}

tstest/integration/tailscaled_deps_test_darwin.go

@@ -18,6 +18,7 @@
 	_ "tailscale.com/drive/driveimpl"
 	_ "tailscale.com/envknob"
 	_ "tailscale.com/health"
+	_ "tailscale.com/hostinfo"
 	_ "tailscale.com/ipn"
 	_ "tailscale.com/ipn/conffile"
 	_ "tailscale.com/ipn/ipnlocal"

tstest/integration/tailscaled_deps_test_freebsd.go

@@ -18,6 +18,7 @@
 	_ "tailscale.com/drive/driveimpl"
 	_ "tailscale.com/envknob"
 	_ "tailscale.com/health"
+	_ "tailscale.com/hostinfo"
 	_ "tailscale.com/ipn"
 	_ "tailscale.com/ipn/conffile"
 	_ "tailscale.com/ipn/ipnlocal"

tstest/integration/tailscaled_deps_test_linux.go

@@ -18,6 +18,7 @@
 	_ "tailscale.com/drive/driveimpl"
 	_ "tailscale.com/envknob"
 	_ "tailscale.com/health"
+	_ "tailscale.com/hostinfo"
 	_ "tailscale.com/ipn"
 	_ "tailscale.com/ipn/conffile"
 	_ "tailscale.com/ipn/ipnlocal"

tstest/integration/tailscaled_deps_test_openbsd.go

@@ -18,6 +18,7 @@
 	_ "tailscale.com/drive/driveimpl"
 	_ "tailscale.com/envknob"
 	_ "tailscale.com/health"
+	_ "tailscale.com/hostinfo"
 	_ "tailscale.com/ipn"
 	_ "tailscale.com/ipn/conffile"
 	_ "tailscale.com/ipn/ipnlocal"

tstest/integration/tailscaled_deps_test_windows.go

@@ -25,6 +25,7 @@
 	_ "tailscale.com/drive/driveimpl"
 	_ "tailscale.com/envknob"
 	_ "tailscale.com/health"
+	_ "tailscale.com/hostinfo"
 	_ "tailscale.com/ipn"
 	_ "tailscale.com/ipn/conffile"
 	_ "tailscale.com/ipn/ipnlocal"