version, hostinfo: recognize gokrazy as a distro

Now:

/tmp/breakglass3929186798 # /user/tailscale debug hostinfo
{
  "IPNVersion": "1.23.0-date.20220107",
  "OS": "linux",
  "OSVersion": "Gokrazy; kernel=5.16.11",
  "DeviceModel": "Raspberry Pi 4 Model B Rev 1.2",
  "Hostname": "gokrazy",
  "GoArch": "arm64"
}

Also, cache the distro lookup. It doesn't change while the program is
running:

name   old time/op    new time/op    delta
Get-6    5.21µs ± 5%    0.00µs ± 3%   -99.91%  (p=0.008 n=5+5)

name   old alloc/op   new alloc/op   delta
Get-6      792B ± 0%        0B       -100.00%  (p=0.008 n=5+5)

name   old allocs/op  new allocs/op  delta
Get-6      8.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)

Updates #1866

Change-Id: Ifb9a63b94287010d3f4c8bfeb6b78119e8a9b203
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

hostinfo/hostinfo_linux.go

@@ -113,6 +113,8 @@ func osVersionLinux() string {
 		return fmt.Sprintf("Synology %s%s", m["productversion"], attr)
 	case distro.OpenWrt:
 		return fmt.Sprintf("OpenWrt %s%s", m["DISTRIB_RELEASE"], attr)
+	case distro.Gokrazy:
+		return fmt.Sprintf("Gokrazy%s", attr)
 	}
 	return fmt.Sprintf("Other%s", attr)
 }

version/distro/distro.go

@@ -8,6 +8,7 @@ package distro
 import (
 	"os"
 	"runtime"
+	"sync/atomic"
 )
 
 type Distro string
@@ -22,17 +23,25 @@ const (
 	Pfsense  = Distro("pfsense")
 	OPNsense = Distro("opnsense")
 	TrueNAS  = Distro("truenas")
+	Gokrazy  = Distro("gokrazy")
 )
 
+var distroAtomic atomic.Value // of Distro
+
 // Get returns the current distro, or the empty string if unknown.
 func Get() Distro {
-	if runtime.GOOS == "linux" {
-		return linuxDistro()
+	d, ok := distroAtomic.Load().(Distro)
+	if ok {
+		return d
 	}
-	if runtime.GOOS == "freebsd" {
-		return freebsdDistro()
+	switch runtime.GOOS {
+	case "linux":
+		d = linuxDistro()
+	case "freebsd":
+		d = freebsdDistro()
 	}
-	return ""
+	distroAtomic.Store(d) // even if empty
+	return d
 }
 
 func have(file string) bool {
@@ -62,6 +71,8 @@ func linuxDistro() Distro {
 		return NixOS
 	case have("/etc/config/uLinux.conf"):
 		return QNAP
+	case haveDir("/gokrazy"):
+		return Gokrazy
 	}
 	return ""
 }

version/distro/distro_test.go

@@ -0,0 +1,16 @@
+// Copyright (c) 2022 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package distro
+
+import "testing"
+
+func BenchmarkGet(b *testing.B) {
+	b.ReportAllocs()
+	var d Distro
+	for i := 0; i < b.N; i++ {
+		d = Get()
+	}
+	_ = d
+}