The initial implementation of NFS direct reads was entirely synchronous.
 The direct read logic issued one NFS READ operation at a time, and waited
 for the server's reply before issuing the next one.  For large direct
 read requests, this is unnecessarily slow.

 This patch changes the NFS direct read path to dispatch NFS READ operations
 for a single direct read request in parallel and wait for them once.  The
 direct read path is still synchronous in nature, but because the NFS READ
 operations are going in parallel, the completion wait should be much shorter.
Signed-off-by: Chuck Lever <cel@netapp.com>
Signed-off-by: Trond Myklebust <trond.myklebust@fys.uio.no>