net.inet6.ip6.deembed_scopeid removal

[Hiroki Sato]

"Alexander V. Chernikov" <melifaro at ipfw.ru> wrote
  in <645741592773762 at mail.yandex.ru>:

me> [re-sending email with as non-html]
me>
me> Hey,
me>
me> I would like to deprecate net.inet6.ip6.deembed_scopeid sysctl while
me> leaving the current default behaviour.
me>
me> This sysctl controls whether IPv6 scope is embedded in the IPv6
me> address or not when reading or writing route/interface/ifaddr data via
me> rtsock/sysctl.
me>
me> Embedding scope in the address is a hack, that overwrites some of the
me> bits that can be used otherwise. It was probably implemented that way
me> to simplify route table interactions, as rtable uses this hack to add
me> link-local addresses to the same radix tree.
me>
me> The change to fix the userland api by filling in sin6_scopeid and
me> avoid touching IPv6 address was added in r243187, 7 years ago. It
me> provided the sysctl in question, allowing to preserve compatibility
me> with older applications, by reverting to the old behavior.
me>
me> 7 years looks like enough timeframe for the applications to be
me> adjusted. Unless any major objections arise, I'm going to remove the
me> code and make de-embedded IPv6 addresses the only option on July 5
me> 2020.

 I agree that it is time to remove it and I do not think we need to
 wait more.  This knob was for debugging purpose rather than for
 keeping compatibility.  A concern was that recovering the scopeid
 might have performance penalty.

-- Hiroki
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