NFSD: Update NFSv3 READDIR entry encoders to use struct xdr_stream

The benefit of the xdr_stream helpers is that they transparently
handle encoding an XDR data item that crosses page boundaries.
Most of the open-coded logic to do that here can be eliminated.

A sub-buffer and sub-stream are set up as a sink buffer for the
directory entry encoder. As an entry is encoded, it is added to
the end of the content in this buffer/stream. The total length of
the directory list is tracked in the buffer's @len field.

When it comes time to encode the Reply, the sub-buffer is merged
into rq_res's page array at the correct place using
xdr_write_pages().

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
diff --git a/fs/nfsd/xdr3.h b/fs/nfsd/xdr3.h
index a4cdd8c..81dea78 100644
--- a/fs/nfsd/xdr3.h
+++ b/fs/nfsd/xdr3.h
@@ -169,20 +169,22 @@ struct nfsd3_linkres {
 };
 
 struct nfsd3_readdirres {
+	/* Components of the reply */
 	__be32			status;
 	struct svc_fh		fh;
-	/* Just to save kmalloc on every readdirplus entry (svc_fh is a
-	 * little large for the stack): */
-	struct svc_fh		scratch;
 	int			count;
 	__be32			verf[2];
-	struct page		**pages;
 
+	/* Used to encode the reply's entry list */
+	struct xdr_stream	xdr;
+	struct xdr_buf		dirlist;
+	struct svc_fh		scratch;
 	struct readdir_cd	common;
 	__be32 *		buffer;
 	int			buflen;
 	__be32 *		offset;
 	__be32 *		offset1;
+	unsigned int		cookie_offset;
 	struct svc_rqst *	rqstp;
 
 };
@@ -309,6 +311,10 @@ int nfs3svc_encode_entry(void *, const char *name,
 int nfs3svc_encode_entry_plus(void *, const char *name,
 				int namlen, loff_t offset, u64 ino,
 				unsigned int);
+int nfs3svc_encode_entry3(void *data, const char *name, int namlen,
+			  loff_t offset, u64 ino, unsigned int d_type);
+int nfs3svc_encode_entryplus3(void *data, const char *name, int namlen,
+			      loff_t offset, u64 ino, unsigned int d_type);
 /* Helper functions for NFSv3 ACL code */
 __be32 *nfs3svc_encode_post_op_attr(struct svc_rqst *rqstp, __be32 *p,
 				struct svc_fh *fhp);