SUNRPC: Convert unwrap data paths to use xdr_stream for replies

We're now moving svcxdr_init_encode() to /before/ the flavor's
->accept method has set rq_auth_slack. Add a helper that can
set rq_auth_slack /after/ svcxdr_init_encode() has been called.
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

include/linux/sunrpc/svc.h

@@ -577,12 +577,34 @@ static inline void svcxdr_init_encode(struct svc_rqst *rqstp)
 	xdr->buf = buf;
 	xdr->iov = resv;
 	xdr->p   = resv->iov_base + resv->iov_len;
-	xdr->end = resv->iov_base + PAGE_SIZE - rqstp->rq_auth_slack;
+	xdr->end = resv->iov_base + PAGE_SIZE;
 	buf->len = resv->iov_len;
 	xdr->page_ptr = buf->pages - 1;
 	buf->buflen = PAGE_SIZE * (rqstp->rq_page_end - buf->pages);
-	buf->buflen -= rqstp->rq_auth_slack;
 	xdr->rqst = NULL;
 }
 
+/**
+ * svcxdr_set_auth_slack -
+ * @rqstp: RPC transaction
+ * @slack: buffer space to reserve for the transaction's security flavor
+ *
+ * Set the request's slack space requirement, and set aside that much
+ * space in the rqstp's rq_res.head for use when the auth wraps the Reply.
+ */
+static inline void svcxdr_set_auth_slack(struct svc_rqst *rqstp, int slack)
+{
+	struct xdr_stream *xdr = &rqstp->rq_res_stream;
+	struct xdr_buf *buf = &rqstp->rq_res;
+	struct kvec *resv = buf->head;
+
+	rqstp->rq_auth_slack = slack;
+
+	xdr->end -= XDR_QUADLEN(slack);
+	buf->buflen -= rqstp->rq_auth_slack;
+
+	WARN_ON(xdr->iov != resv);
+	WARN_ON(xdr->p > xdr->end);
+}
+
 #endif /* SUNRPC_SVC_H */

net/sunrpc/auth_gss/svcauth_gss.c

@@ -1685,24 +1685,22 @@ svcauth_gss_accept(struct svc_rqst *rqstp)
 			svcxdr_init_encode(rqstp);
 			break;
 		case RPC_GSS_SVC_INTEGRITY:
-			/* placeholders for length and seq. number: */
-			svc_putnl(resv, 0);
-			svc_putnl(resv, 0);
+			svcxdr_init_encode(rqstp);
+			/* placeholders for body length and seq. number: */
+			xdr_reserve_space(&rqstp->rq_res_stream, XDR_UNIT * 2);
 			if (svcauth_gss_unwrap_integ(rqstp, gc->gc_seq,
 						     rsci->mechctx))
 				goto garbage_args;
-			rqstp->rq_auth_slack = RPC_MAX_AUTH_SIZE;
-			svcxdr_init_encode(rqstp);
+			svcxdr_set_auth_slack(rqstp, RPC_MAX_AUTH_SIZE);
 			break;
 		case RPC_GSS_SVC_PRIVACY:
-			/* placeholders for length and seq. number: */
-			svc_putnl(resv, 0);
-			svc_putnl(resv, 0);
+			svcxdr_init_encode(rqstp);
+			/* placeholders for body length and seq. number: */
+			xdr_reserve_space(&rqstp->rq_res_stream, XDR_UNIT * 2);
 			if (svcauth_gss_unwrap_priv(rqstp, gc->gc_seq,
 						    rsci->mechctx))
 				goto garbage_args;
-			rqstp->rq_auth_slack = RPC_MAX_AUTH_SIZE * 2;
-			svcxdr_init_encode(rqstp);
+			svcxdr_set_auth_slack(rqstp, RPC_MAX_AUTH_SIZE * 2);
 			break;
 		default:
 			goto auth_err;