[PATCH] tcp: Don't discard window information on keep-alive segments

It looks like a detail, but it's critical if we're dealing with somebody, such as near-future self, using TCP_REPAIR to migrate TCP connections in the guest or container. The last packet sent from the 'source' process/guest/container typically reports a small window, or zero, because the guest/container hadn't been draining it for a while. The next packet, appearing as the target sets TCP_REPAIR_OFF on the migrated socket, is a keep-alive (also called "window probe" in CRIU or TCP_REPAIR-related code), and it comes with an updated window value, reflecting the pre-migration "regular" value. If we ignore it, it might take a while/forever before we realise we can actually restart sending. Fixes: 238c69f9af45 ("tcp: Acknowledge keep-alive segments, ignore them for the rest") Signed-off-by: Stefano Brivio --- tcp.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/tcp.c b/tcp.c index af6bd95..2addf4a 100644 --- a/tcp.c +++ b/tcp.c @@ -1664,8 +1664,10 @@ static int tcp_data_from_tap(const struct ctx *c, struct tcp_tap_conn *conn, tcp_send_flag(c, conn, ACK); tcp_timer_ctl(c, conn); - if (p->count == 1) + if (p->count == 1) { + tcp_tap_window_update(conn, ntohs(th->window)); return 1; + } continue; } -- 2.43.0