Date: Fri, 26 Apr 2024 21:02:34 -0700 From: Bakul Shah <bakul@iitbombay.org> To: Warner Losh <imp@bsdimp.com> Cc: Mike Karels <mike@karels.net>, FreeBSD Net <freebsd-net@freebsd.org> Subject: Re: Question about netinet6/in6.h Message-ID: <E05F30FF-3FAD-4AB3-BA0F-3F1DB594A4D2@iitbombay.org> In-Reply-To: <CANCZdfqEf-TniYhp0Cyv_DnFeKcHKvxeRBotyLYgzN0Jcw5BcQ@mail.gmail.com> References: <CANCZdfrDTktpyW9Ad=3-K9qnVYmY_wCnrmyizvgwJktVfHfV3Q@mail.gmail.com> <229EB3F8-FB68-461C-BF1F-3B2846510EBA@karels.net> <AA706B2F-1C77-47B7-915E-6574E1F3654C@karels.net> <CANCZdfrtxsGKKn3bzaWRDhYphYb0DuZ7VTOWeTbR_8X980u_1A@mail.gmail.com> <4AF50212-9141-44FF-937F-A06AF8B15121@karels.net> <54E63C68-2713-4247-A57C-D3AA9C571327@iitbombay.org> <CANCZdfqEf-TniYhp0Cyv_DnFeKcHKvxeRBotyLYgzN0Jcw5BcQ@mail.gmail.com>
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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?!
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