Re: Question about netinet6/in6.h

On 26 Apr 2024, at 23:02, Bakul Shah wrote:

> On Apr 26, 2024, at 8:41 PM, Warner Losh <imp@bsdimp.com> wrote:
>>
>>
>>
>> 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....
>
> Such defines were typically within #if defined(KERNEL) .. #endif
> so non-kld ports shouldn't be referring to them, right?!

I don't know if that is typical, but in this case the point is to make it
visible to user level.  We don't expect base/ports to do that currently,
but imported programs will.

		Mike