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>

@@ -21,10 +21,14 @@
 
 /*
  * 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>

@@ -241,20 +245,10 @@
         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));