[PATCH net 4/5] rxrpc: Change how the MORE-PACKETS rxrpc wire header flag is driven

[David Howells <dhowells@redhat.com>]

Currently, the MORE-PACKETS rxrpc header flag is set by sendmsg trying to
guess how it should be set by looking to see if there's space in the Tx
window and setting it if there is - long before the packet gets
transmitted (and it gets left in this state).  As a consequence, it's not
very meaningful.

Change this such that it is turned on at the point of transmission if we
have more packets after it in the send buffers and it is left clear if we
don't yet.

Fixes: 17926a79320a ("[AF_RXRPC]: Provide secure RxRPC sockets for use by userspace and kernel both")
cc: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: "David S. Miller" <davem@davemloft.net>
cc: Eric Dumazet <edumazet@google.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: linux-afs@lists.infradead.org
cc: netdev@vger.kernel.org
---
 net/rxrpc/output.c  | 8 +++++++-
 net/rxrpc/sendmsg.c | 3 ---
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/net/rxrpc/output.c b/net/rxrpc/output.c
index bf2d0f847cdb..4ebd0bd40a02 100644
--- a/net/rxrpc/output.c
+++ b/net/rxrpc/output.c
@@ -330,7 +330,7 @@ static void rxrpc_prepare_data_subpacket(struct rxrpc_call *call, struct rxrpc_t
 	struct rxrpc_wire_header *whdr = txb->kvec[0].iov_base;
 	enum rxrpc_req_ack_trace why;
 	struct rxrpc_connection *conn = call->conn;
-	bool last;
+	bool more, last;
 	u8 flags;
 
 	_enter("%x,{%d}", txb->seq, txb->len);
@@ -345,6 +345,12 @@ static void rxrpc_prepare_data_subpacket(struct rxrpc_call *call, struct rxrpc_t
 	flags = txb->flags & RXRPC_TXBUF_WIRE_FLAGS;
 	last = txb->flags & RXRPC_LAST_PACKET;
 
+	more = (!last &&
+		(!list_is_last(&txb->call_link, &call->tx_buffer) ||
+		 !list_empty(&call->tx_sendmsg)));
+	if (more)
+		flags |= RXRPC_MORE_PACKETS;
+
 	/* If our RTT cache needs working on, request an ACK.  Also request
 	 * ACKs if a DATA packet appears to have been lost.
 	 *
diff --git a/net/rxrpc/sendmsg.c b/net/rxrpc/sendmsg.c
index 894b8fa68e5e..eaf4441a340b 100644
--- a/net/rxrpc/sendmsg.c
+++ b/net/rxrpc/sendmsg.c
@@ -384,9 +384,6 @@ static int rxrpc_send_data(struct rxrpc_sock *rx,
 		    (msg_data_left(msg) == 0 && !more)) {
 			if (msg_data_left(msg) == 0 && !more)
 				txb->flags |= RXRPC_LAST_PACKET;
-			else if (call->tx_top - call->acks_hard_ack <
-				 call->tx_winsize)
-				txb->flags |= RXRPC_MORE_PACKETS;
 
 			ret = call->security->secure_packet(call, txb);
 			if (ret < 0)