NFSv4.1: add MDS mount DS only check

The DS only role cannot be used to mount.
Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/client.c

@@ -1453,6 +1453,10 @@ static int nfs4_server_common_setup(struct nfs_server *server,
 	BUG_ON(!server->nfs_client->rpc_ops);
 	BUG_ON(!server->nfs_client->rpc_ops->file_inode_ops);
 
+	/* data servers support only a subset of NFSv4.1 */
+	if (is_ds_only_client(server->nfs_client))
+		return -EPROTONOSUPPORT;
+
 	fattr = nfs_alloc_fattr();
 	if (fattr == NULL)
 		return -ENOMEM;

fs/nfs/nfs4_fs.h

@@ -259,6 +259,13 @@ extern int nfs4_proc_destroy_session(struct nfs4_session *);
 extern int nfs4_init_session(struct nfs_server *server);
 extern int nfs4_proc_get_lease_time(struct nfs_client *clp,
 		struct nfs_fsinfo *fsinfo);
+
+static inline bool
+is_ds_only_client(struct nfs_client *clp)
+{
+	return (clp->cl_exchange_flags & EXCHGID4_FLAG_MASK_PNFS) ==
+		EXCHGID4_FLAG_USE_PNFS_DS;
+}
 #else /* CONFIG_NFS_v4_1 */
 static inline struct nfs4_session *nfs4_get_session(const struct nfs_server *server)
 {
@@ -276,6 +283,12 @@ static inline int nfs4_init_session(struct nfs_server *server)
 {
 	return 0;
 }
+
+static inline bool
+is_ds_only_client(struct nfs_client *clp)
+{
+	return false;
+}
 #endif /* CONFIG_NFS_V4_1 */
 
 extern const struct nfs4_minor_version_ops *nfs_v4_minor_ops[];