From mboxrd@z Thu Jan 1 00:00:00 1970 Received: by passt.top (Postfix, from userid 1000) id AFABC5A026F; Tue, 11 Feb 2025 20:50:51 +0100 (CET) From: Stefano Brivio To: passt-dev@passt.top Subject: [PATCH] tcp: Don't discard window information on keep-alive segments Date: Tue, 11 Feb 2025 20:50:51 +0100 Message-ID: <20250211195051.197798-1-sbrivio@redhat.com> X-Mailer: git-send-email 2.43.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Message-ID-Hash: Z4W2NJWWXBEUFUVYX4GCY6W2R3QKNXIG X-Message-ID-Hash: Z4W2NJWWXBEUFUVYX4GCY6W2R3QKNXIG X-MailFrom: sbrivio@passt.top X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: David Gibson , Jon Maloy X-Mailman-Version: 3.3.8 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: 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