netdev - Re: TCP fast open using experimental TCP option?

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Date:   Tue, 25 Apr 2017 14:00:06 -0700
From:   Yuchung Cheng <ycheng@...gle.com>
To:     Tom Herbert <tom@...bertland.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jerry Chu <hkchu@...gle.com>
Subject: Re: TCP fast open using experimental TCP option?

On Tue, Apr 25, 2017 at 12:08 PM, Tom Herbert <tom@...bertland.com> wrote:
> Looks like TCP fast open was using experimental TCP option at some. Is
> this still needed? Technically this violates usage requirements of
> experimental options. Can this be removed now since there is now an
> assigned option number for TFO?
Given that many clients (e.g. android) have not migrated to 4.0
kernels that support TFO opt 34, I would keep it for backward
compatibility for now.

>
>                              case TCPOPT_EXP:
>                                 /* Fast Open option shares code 254 using a
>                                  * 16 bits magic number.
>                                  */
>                                 if (opsize >= TCPOLEN_EXP_FASTOPEN_BASE &&
>                                     get_unaligned_be16(ptr) ==
>                                     TCPOPT_FASTOPEN_MAGIC)
>                                         tcp_parse_fastopen_option(opsize -
>                                                 TCPOLEN_EXP_FASTOPEN_BASE,
>                                                 ptr + 2, th->syn, foc, true);
>                                 break;