Re: Question about netinet6/in6.h

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.

		Mike