Hi Willy,
> static inline void inet_set_tos(int fd, sa_family_t family, int tos)
> {
> if (family != AF_INET && family != AF_INET6)
> return;
> #if defined(IP_TOS)
> if (setsockopt(fd, IPPROTO_IP, IP_TOS, &tos, sizeof(tos)) == 0)
> return;
> #endif
> #if defined(IPV6_TCLASS)
> if (setsockopt(fd, IPPROTO_IPV6, IPV6_TCLASS, &tos, sizeof(tos) == 0)
> return;
> #endif
> }
Since setsockopt always returns 0, the function will return too early to
set IPV6_TCLASS.
However we can - as per RFC2553 section 3.7 - use the libc macro
IN6_IS_ADDR_V4MAPPED(), to test whether the IPv6 address is actually
a V4-mapped-in-V6 adress (so we set IP_TOS) or a proper IPv6 address (so
we set IPV6_TCLASS).
Instead of the sa_family_t I'm passing the whole sockaddr_storage struct
to the function, so I can access the actual IPv6 address. Let me know if
there are any implications of doing so:
static inline void inet_set_tos(int fd, struct sockaddr_storage from, int tos)
{
#ifdef IP_TOS
if (from.ss_family == AF_INET)
setsockopt(fd, IPPROTO_IP, IP_TOS, &tos, sizeof(tos));
#endif
#ifdef IPV6_TCLASS
if (from.ss_family != AF_INET6)
return;
if (IN6_IS_ADDR_V4MAPPED(&((struct sockaddr_in6 *)&from)->sin6_addr))
setsockopt(fd, IPPROTO_IP, IP_TOS, &tos, sizeof(tos));
else
setsockopt(fd, IPPROTO_IPV6, IPV6_TCLASS, &tos, sizeof(tos));
#endif
}
Thats means we make a single (the correct one) syscall only, and all 3
scenarios (native IPv4, native IPv6 and v4-in-v6-mapped) are covered.
To maintain compatibility we put everything v6 related in #ifdef's of
IPV6_TCLASS.
In case the libc doesn't have that macro, but defines other IPv6 related
things like IPV6_TCLASS, we add a compatibility define in compat.h:
#if defined(IPV6_TCLASS) && !defined(IN6_IS_ADDR_V4MAPPED)
#define IN6_IS_ADDR_V4MAPPED(a) \
((((const uint32_t *) (a))[0] == 0) \
&& (((const uint32_t *) (a))[1] == 0) \
&& (((const uint32_t *) (a))[2] == htonl (0xffff)))
#endif
> We could emit a warning if IPV6_TCLASS is not defined when the set-tos
> is used, but quite frankly, it could upset users who are only using IPV4.
I agree, I didn't think of that. The user may not be able to change the
underlying kernel/libc and a warning can be annoying. Also this is only
interesting for one situation: when IPv6 is used, but IPV6_TCLASS is not
defined, and that particular case will probably never happen in real life.
Let me know if you are ok with the approach above.
Best regards,
Lukas
