add debug code to fix bug: kernel crashed after rmdir the umounted folder, parent->data null

Change-Id: If876cf6e9cba695906fa4a562c34027bd044aed6

fs/vfs/fs_mkdir.c

@@ -50,6 +50,8 @@
 #include "fs/path_cache.h"
 #include "fs/vfs_util.h"
 
+struct Vnode *g_parentOfCoveredVnode = NULL;
+
 /****************************************************************************
  * Private Functions
  ****************************************************************************/
@@ -139,6 +141,11 @@ int do_mkdir(int dirfd, const char *pathname, mode_t mode)
       // alloc name cache failed is not a critical problem, let it go.
       PRINT_ERR("alloc path cache %s failed\n", dirname);
   }
+  if (!strcmp(dirname, "kernel"))
+    {
+        PRINT_ERR("%s-%d: vnode_of_kernel: %p, inode=%p \n", __FUNCTION__, __LINE__, vnode, vnode->data);
+        g_parentOfCoveredVnode = vnode;
+    }
   parentVnode->useCount--;
   VnodeDrop();
 out: