nfs41: Add ability to read RPC call direction on TCP stream.

NFSv4.1 callbacks can arrive over an existing connection. This patch adds
the logic to read the RPC call direction (call or reply). It does this by
updating the state machine to look for the call direction invoking
xs_tcp_read_calldir(...) after reading the XID.

[nfs41: Keep track of RPC call/reply direction with a flag]

As per 11/14/08 review of RFC 53/85.

Add a new flag to track whether the incoming message is an RPC call or an
RPC reply.  TCP_RPC_REPLY is set in the 'struct sock_xprt' tcp_flags in
xs_tcp_read_calldir() if the message is an RPC reply sent on the forechannel.
It is cleared if the message is an RPC request sent on the back channel.

Signed-off-by: Ricardo Labiaga <Ricardo.Labiaga@netapp.com>
Signed-off-by: Benny Halevy <bhalevy@panasas.com>

net/sunrpc/xprtsock.c

@@ -270,6 +270,12 @@ struct sock_xprt {
 #define TCP_RCV_COPY_FRAGHDR	(1UL << 1)
 #define TCP_RCV_COPY_XID	(1UL << 2)
 #define TCP_RCV_COPY_DATA	(1UL << 3)
+#define TCP_RCV_COPY_CALLDIR	(1UL << 4)
+
+/*
+ * TCP RPC flags
+ */
+#define TCP_RPC_REPLY		(1UL << 5)
 
 static inline struct sockaddr *xs_addr(struct rpc_xprt *xprt)
 {
@@ -956,7 +962,7 @@ static inline void xs_tcp_read_fraghdr(struct rpc_xprt *xprt, struct xdr_skb_rea
 	transport->tcp_offset = 0;
 
 	/* Sanity check of the record length */
-	if (unlikely(transport->tcp_reclen < 4)) {
+	if (unlikely(transport->tcp_reclen < 8)) {
 		dprintk("RPC:       invalid TCP record fragment length\n");
 		xprt_force_disconnect(xprt);
 		return;
@@ -991,13 +997,48 @@ static inline void xs_tcp_read_xid(struct sock_xprt *transport, struct xdr_skb_r
 	if (used != len)
 		return;
 	transport->tcp_flags &= ~TCP_RCV_COPY_XID;
-	transport->tcp_flags |= TCP_RCV_COPY_DATA;
+	transport->tcp_flags |= TCP_RCV_COPY_CALLDIR;
 	transport->tcp_copied = 4;
-	dprintk("RPC:       reading reply for XID %08x\n",
+	dprintk("RPC:       reading %s XID %08x\n",
+			(transport->tcp_flags & TCP_RPC_REPLY) ? "reply for"
+							      : "request with",
 			ntohl(transport->tcp_xid));
 	xs_tcp_check_fraghdr(transport);
 }
 
+static inline void xs_tcp_read_calldir(struct sock_xprt *transport,
+				       struct xdr_skb_reader *desc)
+{
+	size_t len, used;
+	u32 offset;
+	__be32	calldir;
+
+	/*
+	 * We want transport->tcp_offset to be 8 at the end of this routine
+	 * (4 bytes for the xid and 4 bytes for the call/reply flag).
+	 * When this function is called for the first time,
+	 * transport->tcp_offset is 4 (after having already read the xid).
+	 */
+	offset = transport->tcp_offset - sizeof(transport->tcp_xid);
+	len = sizeof(calldir) - offset;
+	dprintk("RPC:       reading CALL/REPLY flag (%Zu bytes)\n", len);
+	used = xdr_skb_read_bits(desc, &calldir, len);
+	transport->tcp_offset += used;
+	if (used != len)
+		return;
+	transport->tcp_flags &= ~TCP_RCV_COPY_CALLDIR;
+	transport->tcp_flags |= TCP_RCV_COPY_DATA;
+	transport->tcp_copied += 4;
+	if (ntohl(calldir) == RPC_REPLY)
+		transport->tcp_flags |= TCP_RPC_REPLY;
+	else
+		transport->tcp_flags &= ~TCP_RPC_REPLY;
+	dprintk("RPC:       reading %s CALL/REPLY flag %08x\n",
+			(transport->tcp_flags & TCP_RPC_REPLY) ?
+				"reply for" : "request with", calldir);
+	xs_tcp_check_fraghdr(transport);
+}
+
 static inline void xs_tcp_read_request(struct rpc_xprt *xprt, struct xdr_skb_reader *desc)
 {
 	struct sock_xprt *transport = container_of(xprt, struct sock_xprt, xprt);
@@ -1114,6 +1155,11 @@ static int xs_tcp_data_recv(read_descriptor_t *rd_desc, struct sk_buff *skb, uns
 			xs_tcp_read_xid(transport, &desc);
 			continue;
 		}
+		/* Read in the call/reply flag */
+		if (transport->tcp_flags & TCP_RCV_COPY_CALLDIR) {
+			xs_tcp_read_calldir(transport, &desc);
+			continue;
+		}
 		/* Read in the request data */
 		if (transport->tcp_flags & TCP_RCV_COPY_DATA) {
 			xs_tcp_read_request(xprt, &desc);