cmd/buildlet: remount OpenBSD & FreeBSD filesystems on boot

OpenBSD is deployed and tested. FreeBSD has only been tested by hand,
but this CL doesn't fail the buildlet if the remount fails. It only
logs either way.

Updates golang/go#17104

Change-Id: Ia9662b42ae8305ad9eaa4292c94fa3194cc26b11
Reviewed-on: https://go-review.googlesource.com/29238
Reviewed-by: Matthew Dempsky <[email protected]>

Author: bradfitz

cmd/buildlet/buildlet.go

@@ -91,18 +91,28 @@ func main() {
 	case "macstadium_vm":
 		configureMacStadium()
 	}
-	if runtime.GOOS == "plan9" {
-		log.SetOutput(&plan9LogWriter{w: os.Stderr})
-	}
 	onGCE := metadata.OnGCE()
-	if runtime.GOOS == "linux" && onGCE && !inKube {
-		if w, err := os.OpenFile("/dev/console", os.O_WRONLY, 0); err == nil {
-			log.SetOutput(w)
+	switch runtime.GOOS {
+	case "plan9":
+		log.SetOutput(&plan9LogWriter{w: os.Stderr})
+	case "linux":
+		if onGCE && !inKube {
+			if w, err := os.OpenFile("/dev/console", os.O_WRONLY, 0); err == nil {
+				log.SetOutput(w)
+			}
 		}
 	}
+
 	log.Printf("buildlet starting.")
 	flag.Parse()
 
+	// Optimize emphemeral filesystems. Prefer speed over safety, since these machines
+	// will be gone soon.
+	switch runtime.GOOS {
+	case "openbsd", "freebsd":
+		makeBSDFilesystemFast()
+	}
+
 	if *listenAddr == "AUTO" && *reverse == "" {
 		v := defaultListenAddr()
 		log.Printf("Will listen on %s", v)
@@ -1198,3 +1208,26 @@ func vmwareGetInfo(key string) string {
 	}
 	return strings.TrimSpace(stdout.String())
 }
+
+func makeBSDFilesystemFast() {
+	if !metadata.OnGCE() {
+		log.Printf("Not on GCE; not remounting root filesystem.")
+		return
+	}
+	btype, err := metadata.InstanceAttributeValue("builder-type")
+	if _, ok := err.(metadata.NotDefinedError); ok && len(btype) == 0 {
+		log.Printf("Not remounting root filesystem due to missing builder-type metadata.")
+		return
+	}
+	if err != nil {
+		log.Printf("Not remounting root filesystem due to failure getting builder type instance metadata: %v", err)
+		return
+	}
+	// Tested on OpenBSD and FreeBSD:
+	out, err := exec.Command("/sbin/mount", "-u", "-o", "async,noatime", "/").CombinedOutput()
+	if err != nil {
+		log.Printf("Warning: failed to remount %s root filesystem with async,noatime: %v, %s", runtime.GOOS, err, out)
+		return
+	}
+	log.Printf("Remounted / with async,noatime.")
+}