fix: detect already-mounted path before fs.Mount to avoid macOS hang

README.md

@@ -4,7 +4,7 @@ Read-only FUSE mount that exposes Kubernetes container filesystems locally.
 
 ```bash
 # uses the current kubeconfig context
-$ vifal /mnt/foo-cluster &
+$ vifal /mnt/foo-cluster 2>/tmp/vifal.log &
 
 $ ls /mnt/foo-cluster/
 default  kube-system  monitoring  apps

e2e/tests/zz_mount.sh

@@ -41,10 +41,8 @@ check_clean_unmount "$MOUNT"
 
 remount sigint
 
-if [ "$UNAME_S" != "Darwin" ]; then
-    log_step "double mount fails"
-    must_fail "$VIFAL" $DEBUG "$MOUNT"
-fi
+log_step "double mount fails"
+must_fail "$VIFAL" $DEBUG "$MOUNT"
 
 log_step "SIGINT unmount"
 kill -INT "$VIFAL_PID"

main.go

@@ -139,6 +139,9 @@ Flags:
 	}
 
 	fuseMountpoint = pflag.Arg(0)
+	if isMountpoint(fuseMountpoint) {
+		logger.Fatalf("%s is already a mountpoint", fuseMountpoint)
+	}
 	server, err := fs.Mount(fuseMountpoint, root, &fs.Options{
 		MountOptions: fuse.MountOptions{
 			Name:          *fsName,
@@ -277,6 +280,20 @@ Flags:
 	}
 }
 
+// isMountpoint reports whether path is already a mountpoint by comparing
+// device IDs with its parent (different device = mount boundary).
+// TODO: This should probably be more cleanly handled by go-fuse.
+func isMountpoint(path string) bool {
+	var st, pst syscall.Stat_t
+	if err := syscall.Stat(path, &st); err != nil {
+		return false
+	}
+	if err := syscall.Stat(filepath.Dir(path), &pst); err != nil {
+		return false
+	}
+	return st.Dev != pst.Dev
+}
+
 // doUnmount tries platform-appropriate unmount commands in order.
 func doUnmount(mountpoint string, force bool) error {
 	cmds := [][]string{{"fusermount", "-u", mountpoint}, {"umount", mountpoint}}