Date: Fri, 26 Apr 2024 21:41:09 -0600 From: Warner Losh <imp@bsdimp.com> To: Bakul Shah <bakul@iitbombay.org> Cc: Mike Karels <mike@karels.net>, FreeBSD Net <freebsd-net@freebsd.org> Subject: Re: Question about netinet6/in6.h Message-ID: <CANCZdfqEf-TniYhp0Cyv_DnFeKcHKvxeRBotyLYgzN0Jcw5BcQ@mail.gmail.com> In-Reply-To: <54E63C68-2713-4247-A57C-D3AA9C571327@iitbombay.org> 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>
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On Fri, Apr 26, 2024, 9:33=E2=80=AFPM Bakul Shah <bakul@iitbombay.org> wrot=
e:
>
>
> > On Apr 26, 2024, at 5:02=E2=80=AFPM, Mike Karels <mike@karels.net> wrot=
e:
> >
> > On 26 Apr 2024, at 18:06, Warner Losh wrote:
> >
> >> On Fri, Apr 26, 2024 at 4:21=E2=80=AFPM 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] =3D 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 wit=
h
> >>>> 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 ev=
en
> >>>> in a POSIX environment.
> >>>>
> >>>> I would have no objection to exposing all four definitions, especial=
ly
> >>>> 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 hav=
e
> 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 o=
f
> >> 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 late=
r]
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....
Warner
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<div dir=3D"auto"><div><br><br><div class=3D"gmail_quote"><div dir=3D"ltr" =
class=3D"gmail_attr">On Fri, Apr 26, 2024, 9:33=E2=80=AFPM Bakul Shah <<=
a href=3D"mailto:bakul@iitbombay.org">bakul@iitbombay.org</a>> wrote:<br=
></div><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-=
left:1px #ccc solid;padding-left:1ex"><br>
<br>
> On Apr 26, 2024, at 5:02=E2=80=AFPM, Mike Karels <<a href=3D"mailto=
:mike@karels.net" target=3D"_blank" rel=3D"noreferrer">mike@karels.net</a>&=
gt; wrote:<br>
> <br>
> On 26 Apr 2024, at 18:06, Warner Losh wrote:<br>
> <br>
>> On Fri, Apr 26, 2024 at 4:21=E2=80=AFPM Mike Karels <<a href=3D=
"mailto:mike@karels.net" target=3D"_blank" rel=3D"noreferrer">mike@karels.n=
et</a>> wrote:<br>
>> <br>
>>> On 26 Apr 2024, at 15:49, Mike Karels wrote:<br>
>>> <br>
>>>> On 26 Apr 2024, at 15:01, Warner Losh wrote:<br>
>>>> <br>
>>>>> This has to be a FAQ<br>
>>>>> <br>
>>>>> I'm porting a program from Linux, I often see an e=
rror like:<br>
>>>>> ./test/mock-ifaddrs.c:95:19: error: no member named &#=
39;s6_addr32' in<br>
>>> 'struct<br>
>>>>> in6_addr'<br>
>>>>>=C2=A0 =C2=A095 |=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 =C2=A0 =C2=A0ipv6->sin6_addr.s6_addr32[3] =3D 0;<br>
>>>>>=C2=A0 =C2=A0 =C2=A0 |=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0~~~~~~~~~~~~~~~ ^<br>
>>>>> but yet, we kinda define them, but only for the kernel=
and boot loader:<br>
>>>>> /*<br>
>>>>> * IPv6 address<br>
>>>>> */<br>
>>>>> struct in6_addr {<br>
>>>>>=C2=A0 =C2=A0 =C2=A0 =C2=A0 union {<br>
>>>>>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0=
uint8_t=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0__u6_addr8[16];<br>
>>>>>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0=
uint16_t=C2=A0 =C2=A0 =C2=A0 =C2=A0 __u6_addr16[8];<br>
>>>>>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0=
uint32_t=C2=A0 =C2=A0 =C2=A0 =C2=A0 __u6_addr32[4];<br>
>>>>>=C2=A0 =C2=A0 =C2=A0 =C2=A0 } __u6_addr;=C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 /* 128-bit IP6 addr=
ess */<br>
>>>>> };<br>
>>>>> <br>
>>>>> #define s6_addr=C2=A0 =C2=A0__u6_addr.__u6_addr8<br>
>>>>> #if defined(_KERNEL) || defined(_STANDALONE) /* XXX no=
nstandard */<br>
>>>>> #define s6_addr8=C2=A0 __u6_addr.__u6_addr8<br>
>>>>> #define s6_addr16 __u6_addr.__u6_addr16<br>
>>>>> #define s6_addr32 __u6_addr.__u6_addr32<br>
>>>>> #endif<br>
>>>>> <br>
>>>>> I'm wondering if anybody why it's like that? g=
it blame suggests we<br>
>>> imported<br>
>>>>> that from kame, with<br>
>>>>> only tweaks by people that are now deceased*.*<br>
>>>>> <br>
>>>>> Why not just expose them?<br>
>>>> <br>
>>>> Looks like only s6_addr is specified in the RFCs (2553 and=
3493).=C2=A0 Oddly,<br>
>>>> though, the RFCs give an example implementation using that=
union with<br>
>>>> different element names (like _S6_u8), and show the one #d=
efine.<br>
>>>> Similarly, POSIX specifies only s6_addr, but it allows oth=
er members<br>
>>>> of the structure, so I don't see a problem with exposi=
ng them all even<br>
>>>> in a POSIX environment.<br>
>>>> <br>
>>>> I would have no objection to exposing all four definitions=
, especially<br>
>>>> if Linux apps use them.<br>
>>> <br>
>>> I put the change, along with an explanatory comment, in<br>
>>> <a href=3D"https://reviews.freebsd.org/D44979" rel=3D"noreferr=
er noreferrer" target=3D"_blank">https://reviews.freebsd.org/D44979</a>.=C2=
=A0 Comments welcome.<br>
>>> <br>
>> <br>
>> Thanks! I was testing a similar change, but I like yours better...=
though<br>
>> maybe<br>
>> we should just make it visible when __BSD_VISIBLE is true.... I=
9;ll have to<br>
>> look<br>
>> closely at what Linux does here... I think they have it always vis=
ible, or<br>
>> at least<br>
>> musl does that (glibc is harder to track down due to the many laye=
rs of<br>
>> indirection).<br>
> <br>
> I thought briefly about __BSD_VISIBLE, but wasn't sure it was nece=
ssary.<br>
> Let me know what you find out.=C2=A0 I think it should work either way=
; in.h<br>
> includes cdefs.h, so it's guaranteed to have been included.<br>
<br>
If the -ms-extensions option is used with gcc or clang, this ugliness can<b=
r>
go away as you can have nested anonymous unions or -structs and their field=
s<br>
can be referenced as if they're directly in the parent struct/union.<br=
>
<br>
[IIRC this was present in Plan9 C from very early on. Also in C11 or later]=
</blockquote></div></div><div dir=3D"auto"><br></div><div dir=3D"auto">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 com=
pile there your only hope is this construct....</div><div dir=3D"auto"><br>=
</div><div dir=3D"auto">Warner=C2=A0</div><div dir=3D"auto"></div></div>
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