[PATCH] kNFSd:fix read encoding

encode_read: change 'len' variable from unsigned long to a long for
'(len > 0)' comparison.  don't set up a tail iovec for zero length
reads.

fs/nfsd/nfs4xdr.c

@@ -1691,7 +1691,8 @@ nfsd4_encode_read(struct nfsd4_compoundres *resp, int nfserr, struct nfsd4_read
 {
 	u32 eof;
 	int v, pn;
-	unsigned long maxcount, len;
+	unsigned long maxcount; 
+	long len;
 	ENCODE_HEAD;
 
 	if (nfserr)
@@ -1732,6 +1733,10 @@ nfsd4_encode_read(struct nfsd4_compoundres *resp, int nfserr, struct nfsd4_read
 
 	resp->xbuf->page_len = maxcount;
 
+	/* read zero bytes -> don't set up tail */
+	if(!maxcount)
+		return 0;        
+
 	/* set up page for remaining responses */
 	svc_take_page(resp->rqstp);
 	resp->xbuf->tail[0].iov_base =