主机是OPENSUSE 42.2，NFS服务器配置好，单板可以成功挂载主机的NFS共享文件夹。
就是通过NFS挂载ROOT FS时，始终挂载不上，总是报VFS: Unable to mount root fs via NFS, trying floppy
在OPENSUSE 42.2的官方说明里找NFS配置方法
http://doc.opensuse.org/documentation/leap/reference/html/book.opensuse.reference/cha.nfs.html
有这样的说明：
按说明使用NFSV2，问题解决了。
参考：/etc/sysconfig/nfs
The /etc/sysconfig/nfs file contains a few parameters that determine NFSv4 server daemon behavior. It is important to set the parameter NFS4_SUPPORT to yes (default). NFS4_SUPPORT determines whether the NFS server supports NFSv4 exports and clients.
Tip: Mount Options
On SUSE Linux Enterprise prior to version 12, the --bind mount in /etc/exports was mandatory. It is still supported, but now deprecated. Configuring directories for export with NFSv4 is now the same as with NFSv3.
Note: NFSv2
If NFS clients still depend on NFSv2, enable it on the server in /etc/sysconfig/nfs by setting:
NFSD_OPTIONS="-V2"
MOUNTD_OPTIONS="-V2"
After restarting the service, check whether version 2 is available with the command:
tux > cat /proc/fs/nfsd/versions
+2 +3 +4 +4.1 -4.2