New function nfs4_update_server() moves an nfs_server to a different
nfs_client. This is done as part of migration recovery.
Though it may be appealing to think of them as the same thing,
migration recovery is not the same as following a referral.
For a referral, the client has not descended into the file system
yet: it has no nfs_server, no super block, no inodes or open state.
It is enough to simply instantiate the nfs_server and super block,
and perform a referral mount.
For a migration, however, we have all of those things already, and
they have to be moved to a different nfs_client. No local namespace
changes are needed here.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
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