svn commit: r292823 - in stable/10/sys: conf netinet

[Patrick Kelsey]

On Sun, Dec 27, 2015 at 9:59 PM, Andrey Chernov <ache at freebsd.org> wrote:

> On 28.12.2015 5:43, Patrick Kelsey wrote:
> > Author: pkelsey
> > Date: Mon Dec 28 02:43:12 2015
> > New Revision: 292823
> > URL: https://svnweb.freebsd.org/changeset/base/292823
> >
> > Log:
> >   MFC r292706:
> >
> >   Implementation of server-side TCP Fast Open (TFO) [RFC7413].
> >
> >   TFO is disabled by default in the kernel build.  See the top comment
> >   in sys/netinet/tcp_fastopen.c for implementation particulars.
>
> Why it is disabled by default? Do we need some rc.conf knobs to not deal
> directly with it, like tcp_extensions? OMG, why it is kernel config and
> not boot-time sysctl?
>

This is explained in the top comment in sys/netinet/tcp_fastopen.c, but I
will repeat it here and elaborate a little.  It is disabled by default in
the kernel build as a conservative measure until it is exercised more
widely, given the modifications it introduces to the TCP state machine
code, syncache code, etc.  When you do enable it in the kernel build (and
after some point in the future when it is enabled by default), there is
still a sysctl that governs its availability in the system that must be
enabled before it can be used.

-Patrick