Date: Tue, 9 Jul 2002 14:00:38 -0400 (EDT) From: Kelly Yancey <kbyanc@posi.net> To: Juan Francisco Rodriguez Hervella <jrh@it.uc3m.es> Cc: freebsd-net@FreeBSD.ORG Subject: Re: About "sockaddr_in" and "sockaddr_in6" structures Message-ID: <Pine.BSF.4.05.10207091352310.3338-100000@kronos.networkrichmond.com> In-Reply-To: <3D2AE6BB.7CD0CEC7@it.uc3m.es>
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On Tue, 9 Jul 2002, Juan Francisco Rodriguez Hervella wrote:
> Hello:
>
> I'm seeing that "struct sockaddr_in" has a field like this:
>
> char sin_zero[8];
>
> Why ?
> Could anyone explain me what's used for ?
>
> Could it be bad if I'd add the same field to
> "sockaddr_in6" ?
>
> PS: I'm trying to implement divert sockets for
> IPv6 using the KAME implementation of "ip6fw".
>
> Thanks.
>
> JFRH.
>
The minimum size of a sockaddr's address portion (as defined in
sys/socket.h) is 14 bytes (max is SOCK_MAXADDRLEN = 255); combined with
the size of the sa_len and sa_family fields you get a minimum length of 16
bytes for the entire structure. The sin_zero field of sockaddr_in is to
pad the structure out to this minimum length. Given that a sockaddr_in6
is already larger than the minimum required, there really isn't any point
in adding the padding field to it.
Kelly
--
Kelly Yancey -- kbyanc@{posi.net,FreeBSD.org}
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