[PATCH] RPC: skip over transport-specific heads automatically

 Add a generic mechanism for skipping over transport-specific headers
 when constructing an RPC request.  This removes another "xprt->stream"
 dependency.

 Test-plan:
 Write-intensive workload on a single mount point (try both UDP and
 TCP).
Signed-off-by: Chuck Lever <cel@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

include/linux/sunrpc/msg_prot.h

@@ -76,5 +76,30 @@ enum rpc_auth_stat {
 
 #define RPC_MAXNETNAMELEN	256
 
+/*
+ * From RFC 1831:
+ *
+ * "A record is composed of one or more record fragments.  A record
+ *  fragment is a four-byte header followed by 0 to (2**31) - 1 bytes of
+ *  fragment data.  The bytes encode an unsigned binary number; as with
+ *  XDR integers, the byte order is from highest to lowest.  The number
+ *  encodes two values -- a boolean which indicates whether the fragment
+ *  is the last fragment of the record (bit value 1 implies the fragment
+ *  is the last fragment) and a 31-bit unsigned binary value which is the
+ *  length in bytes of the fragment's data.  The boolean value is the
+ *  highest-order bit of the header; the length is the 31 low-order bits.
+ *  (Note that this record specification is NOT in XDR standard form!)"
+ *
+ * The Linux RPC client always sends its requests in a single record
+ * fragment, limiting the maximum payload size for stream transports to
+ * 2GB.
+ */
+
+typedef u32	rpc_fraghdr;
+
+#define	RPC_LAST_STREAM_FRAGMENT	(1U << 31)
+#define	RPC_FRAGMENT_SIZE_MASK		(~RPC_LAST_STREAM_FRAGMENT)
+#define	RPC_MAX_FRAGMENT_SIZE		((1U << 31) - 1)
+
 #endif /* __KERNEL__ */
 #endif /* _LINUX_SUNRPC_MSGPROT_H_ */

include/linux/sunrpc/xprt.h

@@ -155,6 +155,8 @@ struct rpc_xprt {
 
 	size_t			max_payload;	/* largest RPC payload size,
 						   in bytes */
+	unsigned int		tsh_size;	/* size of transport specific
+						   header */
 
 	struct rpc_wait_queue	sending;	/* requests waiting to send */
 	struct rpc_wait_queue	resend;		/* requests waiting to resend */
@@ -236,6 +238,11 @@ int			xprt_adjust_timeout(struct rpc_rqst *req);
 void			xprt_release(struct rpc_task *task);
 int			xprt_destroy(struct rpc_xprt *xprt);
 
+static inline u32 *xprt_skip_transport_header(struct rpc_xprt *xprt, u32 *p)
+{
+	return p + xprt->tsh_size;
+}
+
 /*
  * Transport switch helper functions
  */

net/sunrpc/auth_gss/auth_gss.c

@@ -844,10 +844,8 @@ gss_marshal(struct rpc_task *task, u32 *p)
 
 	/* We compute the checksum for the verifier over the xdr-encoded bytes
 	 * starting with the xid and ending at the end of the credential: */
-	iov.iov_base = req->rq_snd_buf.head[0].iov_base;
-	if (task->tk_client->cl_xprt->stream)
-		/* See clnt.c:call_header() */
-		iov.iov_base += 4;
+	iov.iov_base = xprt_skip_transport_header(task->tk_xprt,
+					req->rq_snd_buf.head[0].iov_base);
 	iov.iov_len = (u8 *)p - (u8 *)iov.iov_base;
 	xdr_buf_from_iov(&iov, &verf_buf);
 

net/sunrpc/clnt.c

@@ -1075,13 +1075,12 @@ static u32 *
 call_header(struct rpc_task *task)
 {
 	struct rpc_clnt *clnt = task->tk_client;
-	struct rpc_xprt *xprt = clnt->cl_xprt;
 	struct rpc_rqst	*req = task->tk_rqstp;
 	u32		*p = req->rq_svec[0].iov_base;
 
 	/* FIXME: check buffer size? */
-	if (xprt->stream)
-		*p++ = 0;		/* fill in later */
+
+	p = xprt_skip_transport_header(task->tk_xprt, p);
 	*p++ = req->rq_xid;		/* XID */
 	*p++ = htonl(RPC_CALL);		/* CALL */
 	*p++ = htonl(RPC_VERSION);	/* RPC version */

net/sunrpc/xprtsock.c

@@ -282,6 +282,13 @@ static int xs_udp_send_request(struct rpc_task *task)
 	return status;
 }
 
+static inline void xs_encode_tcp_record_marker(struct xdr_buf *buf)
+{
+	u32 reclen = buf->len - sizeof(rpc_fraghdr);
+	rpc_fraghdr *base = buf->head[0].iov_base;
+	*base = htonl(RPC_LAST_STREAM_FRAGMENT | reclen);
+}
+
 /**
  * xs_tcp_send_request - write an RPC request to a TCP socket
  * @task: address of RPC task that manages the state of an RPC request
@@ -301,11 +308,9 @@ static int xs_tcp_send_request(struct rpc_task *task)
 	struct rpc_rqst *req = task->tk_rqstp;
 	struct rpc_xprt *xprt = req->rq_xprt;
 	struct xdr_buf *xdr = &req->rq_snd_buf;
-	u32 *marker = req->rq_svec[0].iov_base;
 	int status, retry = 0;
 
-	/* Write the record marker */
-	*marker = htonl(0x80000000|(req->rq_slen-sizeof(*marker)));
+	xs_encode_tcp_record_marker(&req->rq_snd_buf);
 
 	xs_pktdump("packet data:",
 				req->rq_svec->iov_base,
@@ -503,16 +508,19 @@ static inline void xs_tcp_read_fraghdr(struct rpc_xprt *xprt, skb_reader_t *desc
 	xprt->tcp_offset += used;
 	if (used != len)
 		return;
+
 	xprt->tcp_reclen = ntohl(xprt->tcp_recm);
-	if (xprt->tcp_reclen & 0x80000000)
+	if (xprt->tcp_reclen & RPC_LAST_STREAM_FRAGMENT)
 		xprt->tcp_flags |= XPRT_LAST_FRAG;
 	else
 		xprt->tcp_flags &= ~XPRT_LAST_FRAG;
-	xprt->tcp_reclen &= 0x7fffffff;
+	xprt->tcp_reclen &= RPC_FRAGMENT_SIZE_MASK;
+
 	xprt->tcp_flags &= ~XPRT_COPY_RECM;
 	xprt->tcp_offset = 0;
+
 	/* Sanity check of the record length */
-	if (xprt->tcp_reclen < 4) {
+	if (unlikely(xprt->tcp_reclen < 4)) {
 		dprintk("RPC:      invalid TCP record fragment length\n");
 		xprt_disconnect(xprt);
 		return;
@@ -1065,6 +1073,7 @@ int xs_setup_udp(struct rpc_xprt *xprt, struct rpc_timeout *to)
 
 	xprt->prot = IPPROTO_UDP;
 	xprt->port = XS_MAX_RESVPORT;
+	xprt->tsh_size = 0;
 	xprt->stream = 0;
 	xprt->nocong = 0;
 	xprt->cwnd = RPC_INITCWND;
@@ -1105,11 +1114,12 @@ int xs_setup_tcp(struct rpc_xprt *xprt, struct rpc_timeout *to)
 
 	xprt->prot = IPPROTO_TCP;
 	xprt->port = XS_MAX_RESVPORT;
+	xprt->tsh_size = sizeof(rpc_fraghdr) / sizeof(u32);
 	xprt->stream = 1;
 	xprt->nocong = 1;
 	xprt->cwnd = RPC_MAXCWND(xprt);
 	xprt->resvport = capable(CAP_NET_BIND_SERVICE) ? 1 : 0;
-	xprt->max_payload = (1U << 31) - 1;
+	xprt->max_payload = RPC_MAX_FRAGMENT_SIZE;
 
 	INIT_WORK(&xprt->connect_worker, xs_tcp_connect_worker, xprt);