[PATCH 1/4] tcp: Split handling of DUP_ACK from ACK

[David Gibson <david@gibson.dropbear.id.au>]

The DUP_ACK flag to tcp_send_flag() has two effects: first it forces the
setting of the ACK flag in the packet, even if we otherwise wouldn't.
Secondly, it causes a duplicate of the flags packet to be sent immediately
after the first.

Setting the ACK flag to tcp_send_flag() also has the first effect, so
instead of having DUP_ACK also do that, pass both flags when we need both
operations.  This slightly simplifies the logic of tcp_send_flag() in a way
that makes some future changes easier.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 tcp.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tcp.c b/tcp.c
index a1860d10..edd3d899 100644
--- a/tcp.c
+++ b/tcp.c
@@ -1677,7 +1677,7 @@ static int tcp_send_flag(struct ctx *c, struct tcp_tap_conn *conn, int flags)
 
 		th->ack = !!(flags & ACK);
 	} else {
-		th->ack = !!(flags & (ACK | DUP_ACK)) ||
+		th->ack = !!(flags & ACK)) ||
 			  conn->seq_ack_to_tap != prev_ack_to_tap ||
 			  !prev_wnd_to_tap;
 	}
@@ -2503,7 +2503,7 @@ out:
 		 */
 		if (conn->seq_dup_ack_approx != (conn->seq_from_tap & 0xff)) {
 			conn->seq_dup_ack_approx = conn->seq_from_tap & 0xff;
-			tcp_send_flag(c, conn, DUP_ACK);
+			tcp_send_flag(c, conn, ACK | DUP_ACK);
 		}
 		return p->count - idx;
 	}
-- 
@@ -1677,7 +1677,7 @@ static int tcp_send_flag(struct ctx *c, struct tcp_tap_conn *conn, int flags)
 
 		th->ack = !!(flags & ACK);
 	} else {
-		th->ack = !!(flags & (ACK | DUP_ACK)) ||
+		th->ack = !!(flags & ACK)) ||
 			  conn->seq_ack_to_tap != prev_ack_to_tap ||
 			  !prev_wnd_to_tap;
 	}
@@ -2503,7 +2503,7 @@ out:
 		 */
 		if (conn->seq_dup_ack_approx != (conn->seq_from_tap & 0xff)) {
 			conn->seq_dup_ack_approx = conn->seq_from_tap & 0xff;
-			tcp_send_flag(c, conn, DUP_ACK);
+			tcp_send_flag(c, conn, ACK | DUP_ACK);
 		}
 		return p->count - idx;
 	}
-- 
2.44.0