you tag a socket with an uint32_t value. The cookie can then be
used by the kernel for various purposes, e.g. setting the skipto
rule or pipe number in ipfw (this is the reason SO_USER_COOKIE has
been implemented; however there is nothing ipfw-specific in its
implementation).
The ipfw-related code that uses the optopn will be committed separately.
This change adds a field to 'struct socket', but the struct is not
part of any driver or userland-visible ABI so the change should be
harmless.
See the discussion at
http://lists.freebsd.org/pipermail/freebsd-ipfw/2009-October/004001.html
Idea and code from Paul Joe, small modifications and manpage
changes by myself.
Submitted by: Paul Joe
MFC after: 1 week
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