Re: Question about netinet6/in6.h

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).

Warner