NEX-15279 support NFS server in zone
NEX-15520 online NFS shares cause zoneadm halt to hang in nfs_export_zone_fini
Portions contributed by: Dan Kruchinin dan.kruchinin@nexenta.com
Portions contributed by: Stepan Zastupov stepan.zastupov@gmail.com
Reviewed by: Joyce McIntosh <joyce.mcintosh@nexenta.com>
Reviewed by: Rob Gittins <rob.gittins@nexenta.com>
Reviewed by: Gordon Ross <gordon.ross@nexenta.com>

*** 21,30 ****
--- 21,34 ----
  
  /*
   * Copyright (c) 2007, 2010, Oracle and/or its affiliates. All rights reserved.
   */
  
+ /*
+  * Copyright 2018 Nexenta Systems, Inc.
+  */
+ 
  #include <sys/atomic.h>
  #include <sys/cmn_err.h>
  #include <sys/errno.h>
  #include <sys/mount.h>
  #include <sharefs/sharefs.h>
*** 241,260 ****
          data = vfsp->vfs_data;
          if (data->sharefs_vfs_root->v_count > 1)
                  return (EBUSY);
  
          /*
-          * Only allow an unmount iff there are no entries in memory.
-          */
-         rw_enter(&sharetab_lock, RW_READER);
-         if (sharetab_size != 0) {
-                 rw_exit(&sharetab_lock);
-                 return (EBUSY);
-         }
-         rw_exit(&sharetab_lock);
- 
-         /*
           * Release the last hold on the root vnode
           */
          VN_RELE(data->sharefs_vfs_root);
  
          kmem_free(data, sizeof (sharefs_vfs_t));
--- 245,254 ----