cmount: fix unicode issues with accented characters on macOS

This adds

    -o modules=iconv,from_code=UTF-8,to_code=UTF-8-MAC

To the mount options if it isn't already present which fixes mounting
issues on macOS with accented characters in the finder.

cmd/cmount/mount.go

@@ -12,6 +12,7 @@ import (
 	"fmt"
 	"os"
 	"runtime"
+	"strings"
 	"sync/atomic"
 	"time"
 
@@ -36,6 +37,19 @@ func init() {
 	mountlib.AddRc("cmount", mount)
 }
 
+// Find the option string in the current options
+func findOption(name string, options []string) (found bool) {
+	for _, option := range options {
+		if option == "-o" {
+			continue
+		}
+		if strings.Contains(option, name) {
+			return true
+		}
+	}
+	return false
+}
+
 // mountOptions configures the options from the command line flags
 func mountOptions(VFS *vfs.VFS, device string, mountpoint string, opt *mountlib.Options) (options []string) {
 	// Options
@@ -105,6 +119,13 @@ func mountOptions(VFS *vfs.VFS, device string, mountpoint string, opt *mountlib.
 	for _, option := range opt.ExtraFlags {
 		options = append(options, option)
 	}
+	if runtime.GOOS == "darwin" {
+		if !findOption("modules=iconv", options) {
+			iconv := "modules=iconv,from_code=UTF-8,to_code=UTF-8-MAC"
+			options = append(options, "-o", iconv)
+			fs.Debugf(nil, "Adding \"-o %s\" for macOS", iconv)
+		}
+	}
 	return options
 }