Date: Sat, 27 Apr 2024 06:57:41 -0500 From: Mike Karels <mike@karels.net> To: Bakul Shah <bakul@iitbombay.org> Cc: Warner Losh <imp@bsdimp.com>, FreeBSD Net <freebsd-net@freebsd.org> Subject: Re: Question about netinet6/in6.h Message-ID: <03AAFE2A-8BCE-4E5E-8510-1D5AB58AC363@karels.net> In-Reply-To: <E05F30FF-3FAD-4AB3-BA0F-3F1DB594A4D2@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> <CANCZdfqEf-TniYhp0Cyv_DnFeKcHKvxeRBotyLYgzN0Jcw5BcQ@mail.gmail.com> <E05F30FF-3FAD-4AB3-BA0F-3F1DB594A4D2@iitbombay.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On 26 Apr 2024, at 23:02, Bakul Shah wrote:
> On Apr 26, 2024, at 8:41=E2=80=AFPM, Warner Losh <imp@bsdimp.com> wrote=
:
>>
>>
>>
>> On Fri, Apr 26, 2024, 9:33=E2=80=AFPM Bakul Shah <bakul@iitbombay.org>=
wrote:
>>
>>
>>> On Apr 26, 2024, at 5:02=E2=80=AFPM, Mike Karels <mike@karels.net> wr=
ote:
>>>
>>> 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' i=
n
>>>>> '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 l=
oader:
>>>>>>> /*
>>>>>>> * 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 w=
e
>>>>> 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 w=
ith
>>>>>> different element names (like _S6_u8), and show the one #define.
>>>>>> Similarly, POSIX specifies only s6_addr, but it allows other membe=
rs
>>>>>> 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, especi=
ally
>>>>>> 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... t=
hough
>>>> maybe
>>>> we should just make it visible when __BSD_VISIBLE is true.... I'll h=
ave to
>>>> look
>>>> closely at what Linux does here... I think they have it always visib=
le, 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 necessa=
ry.
>>> Let me know what you find out. I think it should work either way; in=
=2Eh
>>> 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 l=
ater]
>>
>> 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 t=
o 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
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?03AAFE2A-8BCE-4E5E-8510-1D5AB58AC363>