driver inclusion
category: feature
bugzilla: #I7U0W0:[openEuler 20.03 SP4]eNFS特性合入，提升NFS客户端的性能与可靠性

Currently, the NFS client can use only one server IP address at a single mount point. As a result, the hardware capability of multiple storage nodes and NICs cannot be fully utilized. In multiple financial sites, the performance cannot meet service requirements. In addition, when a single link is faulty, services are suspended. The reliability problem needs to be solved.
OpenEuler-based commercial OS vendors hope that the eNFS feature will be integrated into 20.03 SP4 to resolve performance and reliability problems.

When user mount one NFS share, can input localaddrs/remoteaddrs these two optional Parameters to use eNFS multipath. If these optional parameters are not used, NFS will behave as before. For example,
mount -t nfs -o [localaddrs=127.17.0.1-127.17.0.4],[remoteaddrs=127.17.1.1-127.17.1.4] xx.xx.xx.xx:/test /mnt/test

Changes in eNFS are as follows:

1. patch 0001:
   At the NFS layer, the eNFS registration function is called back when the mount command parses parameters. The eNFS parses and saves the IP address list entered by users.
2. patch 0002:
   At the sunrpc layer, the eNFS registration function is called back When the NFS uses sunrpc to create rpc_clnt, the eNFS combines the IP address list entered for mount to generate multiple xprts. When the I/O times out, the callback function of the eNFS is called back so that the eNFS switches to an available link for retry.
3. patch 0003:
   The eNFS module registers the interface for parsing the mount command. During the mount process, the NFS invokes the eNFS interface to enable the eNFS to parse the mounting parameters of UltraPath. The eNFS module saves the mounting parameters to the context of nfs_client.
4. patch 0004:
   When the NFS invokes the SunRPC to create rpc_clnt, the eNFS interface is called back. The eNFS creates multiple xprts based on the output IP address list. When NFS V3 I/Os are delivered, eNFS distributes I/Os to available links based on the link status, improving performance through load balancing.
5. patch 0005:
   When sending I/Os from the SunRPC module to the NFS server times out, the SunRPC module calls back the eNFS module to reselect a link. The eNFS module distributes I/Os to other available links, preventing service interruption caused by a single link failure.
6. patch 0006:
   The eNFS compilation option and makefile are added. By default, the eNFS compilation is not performed.

Signed-off-by: mingqian218472 zhangmingqian.zhang@huawei.com