On Fri, Aug 15, 2025 at 06:10:38PM +0200, Stefano Brivio wrote:
...as I'm going to need a third occurrence of this in the next change.
This introduces a small functional change in tcp_data_from_tap(): the sequence was previously rewound to the highest ACK number we found in the current packet batch, and not to the current value of seq_ack_from_tap.
The two might differ in case tcp_sock_consume() failed, because in that case we're ignoring that ACK altogether. But if we're ignoring it, it looks more correct to me to start retransmitting from an earlier sequence anyway.
Signed-off-by: Stefano Brivio
Reviewed-by: David Gibson
--- tcp.c | 47 ++++++++++++++++++++++++++++++++--------------- 1 file changed, 32 insertions(+), 15 deletions(-)
diff --git a/tcp.c b/tcp.c index 7c1f237..1402ca2 100644 --- a/tcp.c +++ b/tcp.c @@ -1097,6 +1097,26 @@ static void tcp_update_seqack_from_tap(const struct ctx *c, } }
+/** + * tcp_rewind_seq() - Rewind sequence to tap and socket offset to current ACK + * @c: Execution context + * @conn: Connection pointer + * + * Return: 0 on success, -1 on failure, with connection reset + */ +static int tcp_rewind_seq(const struct ctx *c, struct tcp_tap_conn *conn) +{ + conn->seq_to_tap = conn->seq_ack_from_tap; + conn->events &= ~TAP_FIN_SENT; + + if (tcp_set_peek_offset(conn, 0)) { + tcp_rst(c, conn); + return -1; + } + + return 0; +} + /** * tcp_prepare_flags() - Prepare header for flags-only segment (no payload) * @c: Execution context @@ -1757,13 +1777,11 @@ static int tcp_data_from_tap(const struct ctx *c, struct tcp_tap_conn *conn, if (retr) { flow_trace(conn, "fast re-transmit, ACK: %u, previous sequence: %u", - max_ack_seq, conn->seq_to_tap); - conn->seq_to_tap = max_ack_seq; - conn->events &= ~TAP_FIN_SENT; - if (tcp_set_peek_offset(conn, 0)) { - tcp_rst(c, conn); + conn->seq_ack_from_tap, conn->seq_to_tap); + + if (tcp_rewind_seq(c, conn)) return -1; - } + tcp_data_from_sock(c, conn); }
@@ -2285,17 +2303,16 @@ void tcp_timer_handler(const struct ctx *c, union epoll_ref ref) tcp_rst(c, conn); } else { flow_dbg(conn, "ACK timeout, retry"); - conn->retrans++; - conn->seq_to_tap = conn->seq_ack_from_tap; - conn->events &= ~TAP_FIN_SENT; + if (!conn->wnd_from_tap) conn->wnd_from_tap = 1; /* Zero-window probe */ - if (tcp_set_peek_offset(conn, 0)) { - tcp_rst(c, conn); - } else { - tcp_data_from_sock(c, conn); - tcp_timer_ctl(c, conn); - } + + conn->retrans++; + if (tcp_rewind_seq(c, conn)) + return; + + tcp_data_from_sock(c, conn); + tcp_timer_ctl(c, conn); } } else { struct itimerspec new = { { 0 }, { ACT_TIMEOUT, 0 } };
-- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson