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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Josef Bacik <>
Date: Wed, 12 Aug 2015 08:16:22 -0700
Subject: [PATCH] tcp: ack when we get an OOO/lost packet

While adding tcp window scaling support I was finding that I'd get some packet
loss or reordering when transferring from large distances and grub would just
timeout.  This is because we weren't ack'ing when we got our OOO packet, so the
sender didn't know it needed to retransmit anything, so eventually it would fill
the window and stop transmitting, and we'd time out.  Fix this by ACK'ing when
we don't find our next sequence numbered packet.  With this fix I no longer time
out.  Thanks,

Signed-off-by: Josef Bacik <>
 grub-core/net/tcp.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/grub-core/net/tcp.c b/grub-core/net/tcp.c
index 2077f5519b2..fa29a2afc6c 100644
--- a/grub-core/net/tcp.c
+++ b/grub-core/net/tcp.c
@@ -882,7 +882,10 @@ grub_net_recv_tcp_packet (struct grub_net_buff *nb,
 	  grub_priority_queue_pop (sock->pq);
       if (grub_be_to_cpu32 (tcph->seqnr) != sock->their_cur_seq)
-	return GRUB_ERR_NONE;
+	{
+	  ack (sock);
+	  return GRUB_ERR_NONE;
+	}
       while (1)
 	  nb_top_p = grub_priority_queue_top (sock->pq);