Re: Question about netinet6/in6.h
- Reply: Bakul Shah : "Re: Question about netinet6/in6.h"
- In reply to: Bakul Shah : "Re: Question about netinet6/in6.h"
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Date: Sat, 27 Apr 2024 03:41:09 UTC
On Fri, Apr 26, 2024, 9:33 PM Bakul Shah <bakul@iitbombay.org> wrote: > > > > On Apr 26, 2024, at 5:02 PM, Mike Karels <mike@karels.net> wrote: > > > > On 26 Apr 2024, at 18:06, Warner Losh wrote: > > > >> On Fri, Apr 26, 2024 at 4:21 PM Mike Karels <mike@karels.net> wrote: > >> > >>> On 26 Apr 2024, at 15:49, Mike Karels wrote: > >>> > >>>> On 26 Apr 2024, at 15:01, Warner Losh wrote: > >>>> > >>>>> This has to be a FAQ > >>>>> > >>>>> I'm porting a program from Linux, I often see an error like: > >>>>> ./test/mock-ifaddrs.c:95:19: error: no member named 's6_addr32' in > >>> 'struct > >>>>> in6_addr' > >>>>> 95 | ipv6->sin6_addr.s6_addr32[3] = 0; > >>>>> | ~~~~~~~~~~~~~~~ ^ > >>>>> but yet, we kinda define them, but only for the kernel and boot > loader: > >>>>> /* > >>>>> * IPv6 address > >>>>> */ > >>>>> struct in6_addr { > >>>>> union { > >>>>> uint8_t __u6_addr8[16]; > >>>>> uint16_t __u6_addr16[8]; > >>>>> uint32_t __u6_addr32[4]; > >>>>> } __u6_addr; /* 128-bit IP6 address */ > >>>>> }; > >>>>> > >>>>> #define s6_addr __u6_addr.__u6_addr8 > >>>>> #if defined(_KERNEL) || defined(_STANDALONE) /* XXX nonstandard */ > >>>>> #define s6_addr8 __u6_addr.__u6_addr8 > >>>>> #define s6_addr16 __u6_addr.__u6_addr16 > >>>>> #define s6_addr32 __u6_addr.__u6_addr32 > >>>>> #endif > >>>>> > >>>>> I'm wondering if anybody why it's like that? git blame suggests we > >>> imported > >>>>> that from kame, with > >>>>> only tweaks by people that are now deceased*.* > >>>>> > >>>>> Why not just expose them? > >>>> > >>>> Looks like only s6_addr is specified in the RFCs (2553 and 3493). > Oddly, > >>>> though, the RFCs give an example implementation using that union with > >>>> different element names (like _S6_u8), and show the one #define. > >>>> Similarly, POSIX specifies only s6_addr, but it allows other members > >>>> of the structure, so I don't see a problem with exposing them all even > >>>> in a POSIX environment. > >>>> > >>>> I would have no objection to exposing all four definitions, especially > >>>> if Linux apps use them. > >>> > >>> I put the change, along with an explanatory comment, in > >>> https://reviews.freebsd.org/D44979. Comments welcome. > >>> > >> > >> Thanks! I was testing a similar change, but I like yours better... > though > >> maybe > >> we should just make it visible when __BSD_VISIBLE is true.... I'll have > to > >> look > >> closely at what Linux does here... I think they have it always visible, > or > >> at least > >> musl does that (glibc is harder to track down due to the many layers of > >> indirection). > > > > I thought briefly about __BSD_VISIBLE, but wasn't sure it was necessary. > > Let me know what you find out. I think it should work either way; in.h > > includes cdefs.h, so it's guaranteed to have been included. > > If the -ms-extensions option is used with gcc or clang, this ugliness can > go away as you can have nested anonymous unions or -structs and their > fields > can be referenced as if they're directly in the parent struct/union. > > [IIRC this was present in Plan9 C from very early on. Also in C11 or later] True. In fact c11 and newer doesn't need anything on the command line here. If it were only in the kernel then I'd chamge it like thay while I was here... but lots of code in ports will specify c99 + POSIX 2001 and to compile there your only hope is this construct.... Warner