netdev - Re: [RFD] First draft of RDNSS-in-RA support for IPv6 DNS autoconfiguration

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Message-ID: <c6d9bea0706221709h72dfa5bao7f51d4a611950094@mail.gmail.com>
Date:	Fri, 22 Jun 2007 20:09:18 -0400
From:	"C. Scott Ananian" <cscott@...top.org>
To:	"Michael Buesch" <mb@...sch.de>
Cc:	netdev@...r.kernel.org
Subject: Re: [RFD] First draft of RDNSS-in-RA support for IPv6 DNS autoconfiguration

> > diff -ruHpN -X dontdiff linux-2.6.22-rc5-orig/include/net/ip6_rdnss.h
> > linux-2.6.22-rc5/include/net/ip6_rdnss.h
> > --- linux-2.6.22-rc5-orig/include/net/ip6_rdnss.h1969-12-31
> > 19:00:00.000000000 -0500
> > +++ linux-2.6.22-rc5/include/net/ip6_rdnss.h2007-06-21
> > 18:16:33.000000000 -0400 @@ -0,0 +1,58 @@
> > +#ifndef _NET_IP6_RDNSS_H
> > +#define _NET_IP6_RDNSS_H
> > +
> > +#ifdef __KERNEL__
> > +
> > +#include <linux/in6.h>
> > +
> > +struct nd_opt_rdnss {
> > +__u8type;
> > +__u8length;
> > +#if defined(__BIG_ENDIAN_BITFIELD)
> > +__u8priority:4,
> > +open:1,
> > +reserved1:3;
> > +#elif defined(__LITTLE_ENDIAN_BITFIELD)
> > +__u8reserved1:3,
> > +open:1,
> > +priority:4;
> > +#else
> > +# error not little or big endian
> > +#endif
>
> That is not endianess-safe. Don't use foo:x at all
> for stuff where a specific endianess is needed. The
> compiler doesn't make any guarantee about it.

This was copied directly from include/net/ip6_route.h.  I believe that
it does in fact work, and I (for one) find this much more readable
than the alternative.  If it is in fact broken, then
include/net/ip6_route.h (and the 35 other files which use this #ifdef
in this manner) should be fixed.
 --scott

-- 
                         ( http://cscott.net/ )
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