SUNRPC: Restructure svc_tcp_recv_record()

Refactor: svc_recvfrom() is going to be converted to read into
bio_vecs in a moment. Unhook the only other caller,
svc_tcp_recv_record(), which just wants to read the 4-byte stream
record marker into a kvec.

While we're in the area, streamline this helper by straight-lining
the hot path, replace dprintk call sites with tracepoints, and
reduce the number of atomic bit operations in this path.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

include/trace/events/sunrpc.h

@@ -1443,6 +1443,30 @@ TRACE_EVENT(svcsock_new_socket,
 	)
 );
 
+TRACE_EVENT(svcsock_marker,
+	TP_PROTO(
+		const struct svc_xprt *xprt,
+		__be32 marker
+	),
+
+	TP_ARGS(xprt, marker),
+
+	TP_STRUCT__entry(
+		__field(unsigned int, length)
+		__field(bool, last)
+		__string(addr, xprt->xpt_remotebuf)
+	),
+
+	TP_fast_assign(
+		__entry->length = be32_to_cpu(marker) & RPC_FRAGMENT_SIZE_MASK;
+		__entry->last = be32_to_cpu(marker) & RPC_LAST_STREAM_FRAGMENT;
+		__assign_str(addr, xprt->xpt_remotebuf);
+	),
+
+	TP_printk("addr=%s length=%u%s", __get_str(addr),
+		__entry->length, __entry->last ? " (last)" : "")
+);
+
 DECLARE_EVENT_CLASS(svcsock_class,
 	TP_PROTO(
 		const struct svc_xprt *xprt,

net/sunrpc/svcsock.c

@@ -828,47 +828,45 @@ out:
 }
 
 /*
- * Receive fragment record header.
- * If we haven't gotten the record length yet, get the next four bytes.
+ * Receive fragment record header into sk_marker.
  */
-static int svc_tcp_recv_record(struct svc_sock *svsk, struct svc_rqst *rqstp)
+static ssize_t svc_tcp_read_marker(struct svc_sock *svsk,
+				   struct svc_rqst *rqstp)
 {
-	struct svc_serv	*serv = svsk->sk_xprt.xpt_server;
-	unsigned int want;
-	int len;
+	ssize_t want, len;
 
+	/* If we haven't gotten the record length yet,
+	 * get the next four bytes.
+	 */
 	if (svsk->sk_tcplen < sizeof(rpc_fraghdr)) {
+		struct msghdr	msg = { NULL };
 		struct kvec	iov;
 
 		want = sizeof(rpc_fraghdr) - svsk->sk_tcplen;
 		iov.iov_base = ((char *)&svsk->sk_marker) + svsk->sk_tcplen;
 		iov.iov_len  = want;
-		len = svc_recvfrom(rqstp, &iov, 1, want, 0);
+		iov_iter_kvec(&msg.msg_iter, READ, &iov, 1, want);
+		len = sock_recvmsg(svsk->sk_sock, &msg, MSG_DONTWAIT);
 		if (len < 0)
-			goto error;
+			return len;
 		svsk->sk_tcplen += len;
-
 		if (len < want) {
-			dprintk("svc: short recvfrom while reading record "
-				"length (%d of %d)\n", len, want);
-			return -EAGAIN;
+			/* call again to read the remaining bytes */
+			goto err_short;
 		}
-
-		dprintk("svc: TCP record, %d bytes\n", svc_sock_reclen(svsk));
+		trace_svcsock_marker(&svsk->sk_xprt, svsk->sk_marker);
 		if (svc_sock_reclen(svsk) + svsk->sk_datalen >
-							serv->sv_max_mesg) {
-			net_notice_ratelimited("RPC: fragment too large: %d\n",
-					svc_sock_reclen(svsk));
-			goto err_delete;
-		}
+		    svsk->sk_xprt.xpt_server->sv_max_mesg)
+			goto err_too_large;
 	}
-
 	return svc_sock_reclen(svsk);
-error:
-	dprintk("RPC: TCP recv_record got %d\n", len);
-	return len;
-err_delete:
+
+err_too_large:
+	net_notice_ratelimited("svc: %s %s RPC fragment too large: %d\n",
+			       __func__, svsk->sk_xprt.xpt_server->sv_name,
+			       svc_sock_reclen(svsk));
 	set_bit(XPT_CLOSE, &svsk->sk_xprt.xpt_flags);
+err_short:
 	return -EAGAIN;
 }
 
@@ -961,12 +959,13 @@ static int svc_tcp_recvfrom(struct svc_rqst *rqstp)
 		test_bit(XPT_CONN, &svsk->sk_xprt.xpt_flags),
 		test_bit(XPT_CLOSE, &svsk->sk_xprt.xpt_flags));
 
-	len = svc_tcp_recv_record(svsk, rqstp);
+	clear_bit(XPT_DATA, &svsk->sk_xprt.xpt_flags);
+	len = svc_tcp_read_marker(svsk, rqstp);
 	if (len < 0)
 		goto error;
 
 	base = svc_tcp_restore_pages(svsk, rqstp);
-	want = svc_sock_reclen(svsk) - (svsk->sk_tcplen - sizeof(rpc_fraghdr));
+	want = len - (svsk->sk_tcplen - sizeof(rpc_fraghdr));
 
 	vec = rqstp->rq_vec;