From 480274787d7e3458bc5a7cfbbbe07033984ad711 Mon Sep 17 00:00:00 2001 From: Jason Baron Date: Wed, 23 Oct 2019 11:09:26 -0400 Subject: tcp: add TCP_INFO status for failed client TFO The TCPI_OPT_SYN_DATA bit as part of tcpi_options currently reports whether or not data-in-SYN was ack'd on both the client and server side. We'd like to gather more information on the client-side in the failure case in order to indicate the reason for the failure. This can be useful for not only debugging TFO, but also for creating TFO socket policies. For example, if a middle box removes the TFO option or drops a data-in-SYN, we can can detect this case, and turn off TFO for these connections saving the extra retransmits. The newly added tcpi_fastopen_client_fail status is 2 bits and has the following 4 states: 1) TFO_STATUS_UNSPEC Catch-all state which includes when TFO is disabled via black hole detection, which is indicated via LINUX_MIB_TCPFASTOPENBLACKHOLE. 2) TFO_COOKIE_UNAVAILABLE If TFO_CLIENT_NO_COOKIE mode is off, this state indicates that no cookie is available in the cache. 3) TFO_DATA_NOT_ACKED Data was sent with SYN, we received a SYN/ACK but it did not cover the data portion. Cookie is not accepted by server because the cookie may be invalid or the server may be overloaded. 4) TFO_SYN_RETRANSMITTED Data was sent with SYN, we received a SYN/ACK which did not cover the data after at least 1 additional SYN was sent (without data). It may be the case that a middle-box is dropping data-in-SYN packets. Thus, it would be more efficient to not use TFO on this connection to avoid extra retransmits during connection establishment. These new fields do not cover all the cases where TFO may fail, but other failures, such as SYN/ACK + data being dropped, will result in the connection not becoming established. And a connection blackhole after session establishment shows up as a stalled connection. Signed-off-by: Jason Baron Cc: Eric Dumazet Cc: Neal Cardwell Cc: Christoph Paasch Cc: Yuchung Cheng Acked-by: Yuchung Cheng Signed-off-by: David S. Miller --- include/linux/tcp.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include/linux/tcp.h') diff --git a/include/linux/tcp.h b/include/linux/tcp.h index 668e25a76d69..ca6f01531e64 100644 --- a/include/linux/tcp.h +++ b/include/linux/tcp.h @@ -223,7 +223,7 @@ struct tcp_sock { fastopen_connect:1, /* FASTOPEN_CONNECT sockopt */ fastopen_no_cookie:1, /* Allow send/recv SYN+data without a cookie */ is_sack_reneg:1, /* in recovery from loss with SACK reneg? */ - unused:2; + fastopen_client_fail:2; /* reason why fastopen failed */ u8 nonagle : 4,/* Disable Nagle algorithm? */ thin_lto : 1,/* Use linear timeouts for thin streams */ recvmsg_inq : 1,/* Indicate # of bytes in queue upon recvmsg */ -- cgit v1.2.3-58-ga151