mount: notice daemon dying much quicker

Before this change we waited until until the timeout to check the
daemon was alive.

Now we check it every 100ms like we do the mount status.

This also fixes compiling on all platforms which was broken by the
previous change

9bfbf2a4a mount: fix macOS not noticing errors with --daemon

See: https://forum.rclone.org/t/rclone-mount-daemon-exits-successfully-even-when-mount-fails/43146

cmd/mountlib/mount.go

@@ -10,7 +10,6 @@ import (
 	"runtime"
 	"strings"
 	"sync"
-	"syscall"
 	"time"
 
 	"github.com/rclone/rclone/cmd"
@@ -157,6 +156,38 @@ func AddFlags(flagSet *pflag.FlagSet) {
 	flags.DurationVarP(flagSet, &Opt.DaemonWait, "daemon-wait", "", Opt.DaemonWait, "Time to wait for ready mount from daemon (maximum time on Linux, constant sleep time on OSX/BSD) (not supported on Windows)", "Mount")
 }
 
+const (
+	pollInterval = 100 * time.Millisecond
+)
+
+// WaitMountReady waits until mountpoint is mounted by rclone.
+//
+// If the mount daemon dies prematurely it will notice too.
+func WaitMountReady(mountpoint string, timeout time.Duration, daemon *os.Process) (err error) {
+	endTime := time.Now().Add(timeout)
+	for {
+		if CanCheckMountReady {
+			err = CheckMountReady(mountpoint)
+			if err == nil {
+				break
+			}
+		}
+		err = daemonize.Check(daemon)
+		if err != nil {
+			return err
+		}
+		delay := time.Until(endTime)
+		if delay <= 0 {
+			break
+		}
+		if delay > pollInterval {
+			delay = pollInterval
+		}
+		time.Sleep(delay)
+	}
+	return
+}
+
 // NewMountCommand makes a mount command with the given name and Mount function
 func NewMountCommand(commandName string, hidden bool, mount MountFn) *cobra.Command {
 	var commandDefinition = &cobra.Command{
@@ -220,16 +251,9 @@ func NewMountCommand(commandName string, hidden bool, mount MountFn) *cobra.Comm
 				handle := atexit.Register(func() {
 					killDaemon("Got interrupt")
 				})
-				err = WaitMountReady(mnt.MountPoint, Opt.DaemonWait)
+				err = WaitMountReady(mnt.MountPoint, Opt.DaemonWait, daemon)
 				if err != nil {
 					killDaemon("Daemon timed out")
-				} else {
-					// Double check daemon is still alive
-					// on non Linux OSes WaitMountReady is just a no-op
-					err = daemon.Signal(syscall.Signal(0))
-					if err != nil {
-						err = fmt.Errorf("daemon has died: %w", err)
-					}
 				}
 				atexit.Unregister(handle)
 			}