Re: Question about netinet6/in6.h

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.

		Mike