Remove another class of rpciod deadlocks on HIGHMEM systems. Kick habit of
keeping pages kmap()ed for the entire duration of NFS
read/readdir/readlink operations.

Use struct page directly in RPC client data receive buffer. TCP and UDP
sk->data_ready() bottom-halves copy (and checksum when needed) data into
pages rather than iovecs. atomic_kmap() of single pages is used for the
copy.

include/linux/xdr.h
   Declare structure for copying an sk_buff here rather than in xprt.c.
   Forward declaration of new functions.

include/linux/sunrpc/xprt.h
   RPC client receive buffer changed to use new format 'struct xdr_buf'.

net/sunrpc/clnt.c
   Initialize new format receive buffer.

net/sunrpc/sunrpc_syms.c
   Export xdr_inline_pages(), xdr_shift_buf()

net/sunrpc/xdr.c
   xdr_inline_pages() inlines pages into the receive buffer.
   xdr_partial_copy_from_skb() replaces csum_partial_copy_to_page_cache()
	and copy code in tcp_read_request(). Provides sendfile()-style
	method for copying data from an skb into a struct xdr_buf.
   xdr_shift_buf() replaces xdr_shift_iovec() for when we overestimate
	the size of the RPC/NFS header.

net/sunrpc/xprt.c
   Adapt UDP and TCP receive routines to use new format xdr_buf.

include/linux/nfs_xdr.h
   struct nfs_readargs, nfs_readdirargs, nfs_readlinkargs,
	nfs3_readdirargs, nfs3_readlinkargs all transmit page information.
   struct nfs_readdirres, nfs_readlinkres, nfs3_readlinkres obsoleted.
   struct nfs_rpc_ops->readlink(), readdir(), read() now send pages

fs/nfs/dir.c
   Adapt to new format ->readdir().
   Avoid kmap() around the RPC call.

fs/nfs/read.c
   Adapt to new format ->read() and struct nfs_readargs.

fs/nfs/symlink.c
   Adapt to new format ->readlink().

fs/nfs/proc.c
   Convert nfs_proc_readlink(), nfs_proc_readdir(), nfs_proc_read()

fs/nfs/nfs2xdr.c
   Convert XDR routines to transmit page information.
   Remove duplicate zeroing of pages when server returns a short read.

fs/nfs/nfs3proc.c
   Convert nfs3_proc_readlink(),nfs3_proc_readdir(),nfs3_proc_read()

fs/nfs/nfs3xdr.c
   Convert XDR routines to transmit page information.
   Remove duplicate zeroing of pages when server returns a short read.

Cheers,
  Trond