Use new arg "-notifypid" for more robust daemonization

No more string matching on the parent command line!

TODO.md

@@ -1,4 +1,3 @@
-* More robust daemonization, add cli parameter "--sendusr1=pid"
 * Add test filesystem for "--masterkey" containing an "It works!" file
 * Add fcntl file locking to make multiple concurrent mounts safe
  * add test case

daemonize.go

@@ -21,7 +21,8 @@ func waitForUsr1() {
 func daemonize() {
 	go waitForUsr1()
 	name := os.Args[0]
-	newArgs := []string{"-f"}
+	notifyArg := fmt.Sprintf("-notifypid=%d", os.Getpid())
+	newArgs := []string{"-f", notifyArg}
 	newArgs = append(newArgs, os.Args[1:]...)
 	c := exec.Command(name, newArgs...)
 	c.Stdout = os.Stdout

main.go

@@ -68,7 +68,7 @@ type argContainer struct {
 			plaintextnames, quiet bool
 		masterkey, mountpoint, cipherdir string
 		cpuprofile *string
-		sendusr1 int
+		notifypid int
 }
 
 var flagSet *flag.FlagSet
@@ -93,7 +93,7 @@ func main() {
 	flagSet.BoolVar(&args.quiet, "q", false, "Quiet - silence informational messages")
 	flagSet.StringVar(&args.masterkey, "masterkey", "", "Mount with explicit master key")
 	args.cpuprofile = flagSet.String("cpuprofile", "", "Write cpu profile to specified file")
-	flagSet.IntVar(&args.sendusr1, "sendusr1", 0,
+	flagSet.IntVar(&args.notifypid, "notifypid", 0,
 		"Send USR1 to the specified process after successful mount - used internally for daemonization")
 	flagSet.Parse(os.Args[1:])
 	if args.version {
@@ -221,8 +221,10 @@ func main() {
 	}
 
 	cryptfs.Info.Println("Filesystem ready.")
-	// Send notification to our parent
-	sendUsr1()
+	// Send USR1 notification
+	if args.notifypid > 0 {
+		sendUsr1(args.notifypid)
+	}
 	// Wait for SIGING in the background and unmount ourselves if we get it
 	// This prevents a dangling "Transport endpoint is not connected" mountpoint
 	handleSigint(srv, args.mountpoint)

sendusr1.go

@@ -1,38 +1,21 @@
 package main
 
 import (
-	"bytes"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"syscall"
 )
 
-const (
-	wrapperContains = "gocryptfs\000"
-)
-
-// Send USR1 to the parent process. This notifies it that the
-// mounting has completed sucessfully.
-//
-// Checks /proc/$PPID/cmdline to make sure we do not kill an unrelated process.
-func sendUsr1() {
-	ppid := os.Getppid()
-	fn := fmt.Sprintf("/proc/%d/cmdline", ppid)
-	cmdline, err := ioutil.ReadFile(fn)
+// Send signal USR1 to "pid" (usually our parent process). This notifies it
+// that the mounting has completed sucessfully.
+func sendUsr1(pid int) {
+	p, err := os.FindProcess(pid)
 	if err != nil {
-		fmt.Printf("sendUsr1: ReadFile: %v\n", err)
+		fmt.Printf("sendUsr1: FindProcess: %v\n", err)
 		return
 	}
-	if bytes.Contains(cmdline, []byte(wrapperContains)) {
-		p, err := os.FindProcess(ppid)
-		if err != nil {
-			fmt.Printf("sendUsr1: FindProcess: %v\n", err)
-			return
-		}
-		err = p.Signal(syscall.SIGUSR1)
-		if err != nil {
-			fmt.Printf("sendUsr1: Signal: %v\n", err)
-		}
+	err = p.Signal(syscall.SIGUSR1)
+	if err != nil {
+		fmt.Printf("sendUsr1: Signal: %v\n", err)
 	}
 }