[PATCH RFT 2/5] tcp: Reset STALLED flag on ACK only, check for pending socket data

[Stefano Brivio <sbrivio@redhat.com>]

In tcp_tap_handler(), we shouldn't reset the STALLED flag (indicating
that we ran out of tap-side window space, or that all available
socket data is already in flight -- better names welcome!) on any
event: do that only if the first packet in a batch has the ACK flag
set.

Make sure we check for pending socket data when we reset it:
reverting back to level-triggered epoll events, as tcp_epoll_ctl()
does, isn't guaranteed to actually trigger a socket event.

Further, note that the flag only makes sense once a connection is
established, so move all this to the right place, which is convenient
for the next patch, as we want to check if the STALLED flag was set
before processing any new information about the window size
advertised by the tap.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
 tcp.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/tcp.c b/tcp.c
index aa1c8c9..5528e05 100644
--- a/tcp.c
+++ b/tcp.c
@@ -2572,8 +2572,6 @@ int tcp_tap_handler(struct ctx *c, int af, const void *saddr, const void *daddr,
 	if (th->ack && !(conn->events & ESTABLISHED))
 		tcp_update_seqack_from_tap(c, conn, ntohl(th->ack_seq));
 
-	conn_flag(c, conn, ~STALLED);
-
 	/* Establishing connection from socket */
 	if (conn->events & SOCK_ACCEPTED) {
 		if (th->syn && th->ack && !th->fin) {
@@ -2631,6 +2629,11 @@ int tcp_tap_handler(struct ctx *c, int af, const void *saddr, const void *daddr,
 	if (conn->seq_ack_to_tap != conn->seq_from_tap)
 		ack_due = 1;
 
+	if ((conn->flags & STALLED) && th->ack) {
+		conn_flag(c, conn, ~STALLED);
+		tcp_data_from_sock(c, conn);
+	}
+
 	if ((conn->events & TAP_FIN_RCVD) && !(conn->events & SOCK_FIN_SENT)) {
 		shutdown(conn->sock, SHUT_WR);
 		conn_event(c, conn, SOCK_FIN_SENT);
-- 
@@ -2572,8 +2572,6 @@ int tcp_tap_handler(struct ctx *c, int af, const void *saddr, const void *daddr,
 	if (th->ack && !(conn->events & ESTABLISHED))
 		tcp_update_seqack_from_tap(c, conn, ntohl(th->ack_seq));
 
-	conn_flag(c, conn, ~STALLED);
-
 	/* Establishing connection from socket */
 	if (conn->events & SOCK_ACCEPTED) {
 		if (th->syn && th->ack && !th->fin) {
@@ -2631,6 +2629,11 @@ int tcp_tap_handler(struct ctx *c, int af, const void *saddr, const void *daddr,
 	if (conn->seq_ack_to_tap != conn->seq_from_tap)
 		ack_due = 1;
 
+	if ((conn->flags & STALLED) && th->ack) {
+		conn_flag(c, conn, ~STALLED);
+		tcp_data_from_sock(c, conn);
+	}
+
 	if ((conn->events & TAP_FIN_RCVD) && !(conn->events & SOCK_FIN_SENT)) {
 		shutdown(conn->sock, SHUT_WR);
 		conn_event(c, conn, SOCK_FIN_SENT);
-- 
2.39.2