netdev - Re: Redefinition of struct in6_addr in <netinet/in.h> and <linux/in6.h>

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Date:	Sun, 20 Jan 2013 19:54:47 -0500
From:	Mike Frysinger <vapier@...too.org>
To:	Pedro Alves <palves@...hat.com>
Cc:	YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>,
	"Carlos O'Donell" <carlos@...temhalted.org>,
	David Miller <davem@...emloft.net>, libc-alpha@...rceware.org,
	bhutchings@...arflare.com, amwang@...hat.com, tmb@...eia.org,
	eblake@...hat.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, libvirt-list@...hat.com,
	tgraf@...g.ch, schwab@...e.de
Subject: Re: Redefinition of struct in6_addr in <netinet/in.h> and <linux/in6.h>

On Friday 18 January 2013 09:36:35 Pedro Alves wrote:
> On 01/18/2013 02:24 PM, YOSHIFUJI Hideaki wrote:
> >>>> It's simple enough to move all of the __GLIBC__ uses into
> >>>> libc-compat.h, then you control userspace libc coordination from one
> >>>> file.
> >>> 
> >>> How about just deciding on a single macro/symbol both the
> >>> kernel and libc (any libc that needs this) define?  Something
> >>> like both the kernel and userland doing:
> >>> 
> >>> #ifndef __IPV6_BITS_DEFINED
> >>> #define __IPV6_BITS_DEFINED
> >>> ...
> >>> define in6_addr, sockaddr_in6, ipv6_mreq, whatnot
> >>> #endif
> > 
> > Hmm, how should we handle future structs/enums then?
> > For example, if I want to have in6_flowlabel_req{} defined in
> > glibc, what should we do?
> 
> Include the glibc header first?  Or is this some other
> use case?
> 
> The point wasn't that you'd have only one macro for all
> structs/enums (you could split into __IPV6_IN6_ADDR_DEFINED,
> __IPV6_SOCKADDR_IN6_DEFINED, etc.) but to have the kernel
> and libc agree on guard macros, instead of having the kernel
> do #ifdef __GLIBC__ and glibc doing #ifdef _NETINET_IN_H.
> 
> But as Carlos says, the devil is in the details, and
> I sure am not qualified on the details here.

i shipped some kernel header versions in Gentoo where the linux network 
headers would include the C library's header (as defined by POSIX) so the 
structs that were the same would only come from glibc.  the only reported 
breakage was due to defines that the kernel provided but glibc did not.
-mike

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