mount: add --async-read flag to disable asynchronous reads

See: https://forum.rclone.org/t/constantly-high-iowait-add-log/14156

cmd/mount/mount.go

@@ -32,12 +32,14 @@ func mountOptions(device string) (options []fuse.MountOption) {
 		fuse.Subtype("rclone"),
 		fuse.FSName(device),
 		fuse.VolumeName(mountlib.VolumeName),
-		fuse.AsyncRead(),
 
 		// Options from benchmarking in the fuse module
 		//fuse.MaxReadahead(64 * 1024 * 1024),
 		//fuse.WritebackCache(),
 	}
+	if mountlib.AsyncRead {
+		options = append(options, fuse.AsyncRead())
+	}
 	if mountlib.NoAppleDouble {
 		options = append(options, fuse.NoAppleDouble())
 	}

cmd/mountlib/mount.go

@@ -36,6 +36,7 @@ var (
 	NoAppleDouble      = true        // use noappledouble by default
 	NoAppleXattr       = false       // do not use noapplexattr by default
 	DaemonTimeout      time.Duration // OSXFUSE only
+	AsyncRead          = true        // do async reads by default
 )
 
 // Global constants
@@ -356,6 +357,7 @@ be copied to the vfs cache before opening with --vfs-cache-mode full.
 	flags.BoolVarP(cmdFlags, &Daemon, "daemon", "", Daemon, "Run mount as a daemon (background mode).")
 	flags.StringVarP(cmdFlags, &VolumeName, "volname", "", VolumeName, "Set the volume name (not supported by all OSes).")
 	flags.DurationVarP(cmdFlags, &DaemonTimeout, "daemon-timeout", "", DaemonTimeout, "Time limit for rclone to respond to kernel (not supported by all OSes).")
+	flags.BoolVarP(cmdFlags, &AsyncRead, "async-read", "", AsyncRead, "Use asynchronous reads.")
 
 	if runtime.GOOS == "darwin" {
 		flags.BoolVarP(cmdFlags, &NoAppleDouble, "noappledouble", "", NoAppleDouble, "Sets the OSXFUSE option noappledouble.")