NFS: Simplify ->decode_dirent() calling sequence

Clean up.

The pointer returned by ->decode_dirent() is no longer used as a
pointer.  The only call site (xdr_decode() in fs/nfs/dir.c) simply
extracts the errno value encoded in the pointer.  Replace the
returned pointer with a standard integer errno return value.

Also, pass the "server" argument as part of the nfs_entry instead of
as a separate parameter.  It's faster to derive "server" in
nfs_readdir_xdr_to_array() since we already have the directory's inode
handy.  "server" ought to be invariant for a set of entries in the
same directory, right?

The legacy versions of decode_dirent() don't use "server" anyway, so
it's wasted work for them to derive and pass "server" for each entry.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
index 6c6a995..435eae3 100644
--- a/fs/nfs/internal.h
+++ b/fs/nfs/internal.h
@@ -187,15 +187,18 @@
 /* nfs2xdr.c */
 extern int nfs_stat_to_errno(enum nfs_stat);
 extern struct rpc_procinfo nfs_procedures[];
-extern __be32 *nfs2_decode_dirent(struct xdr_stream *, struct nfs_entry *, struct nfs_server *, int);
+extern int nfs2_decode_dirent(struct xdr_stream *,
+				struct nfs_entry *, int);
 
 /* nfs3xdr.c */
 extern struct rpc_procinfo nfs3_procedures[];
-extern __be32 *nfs3_decode_dirent(struct xdr_stream *, struct nfs_entry *, struct nfs_server *, int);
+extern int nfs3_decode_dirent(struct xdr_stream *,
+				struct nfs_entry *, int);
 
 /* nfs4xdr.c */
 #ifdef CONFIG_NFS_V4
-extern __be32 *nfs4_decode_dirent(struct xdr_stream *, struct nfs_entry *, struct nfs_server *, int);
+extern int nfs4_decode_dirent(struct xdr_stream *,
+				struct nfs_entry *, int);
 #endif
 #ifdef CONFIG_NFS_V4_1
 extern const u32 nfs41_maxread_overhead;