Re: Question about netinet6/in6.h
- Reply: Warner Losh : "Re: Question about netinet6/in6.h"
- In reply to: Mike Karels : "Re: Question about netinet6/in6.h"
- Go to: [ bottom of page ] [ top of archives ] [ this month ]
Date: Sat, 27 Apr 2024 03:33:03 UTC
> 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]