A decade ago commit 6d08acd2d3 ("in6: fix conflict with glibc")
hid the definitions of IPV6 options, because GCC was complaining
about duplicates. The commit did not list the warnings seen, but
trying to recreate them now I think they are (building iproute2):
In file included from ./include/uapi/rdma/rdma_user_cm.h:39,
from rdma.h:16,
from res.h:9,
from res-ctx.c:7:
../include/uapi/linux/in6.h:171:9: warning: ‘IPV6_ADD_MEMBERSHIP’ redefined
171 | #define IPV6_ADD_MEMBERSHIP 20
| ^~~~~~~~~~~~~~~~~~~
In file included from /usr/include/netinet/in.h:37,
from rdma.h:13:
/usr/include/bits/in.h:233:10: note: this is the location of the previous definition
233 | # define IPV6_ADD_MEMBERSHIP IPV6_JOIN_GROUP
| ^~~~~~~~~~~~~~~~~~~
../include/uapi/linux/in6.h:172:9: warning: ‘IPV6_DROP_MEMBERSHIP’ redefined
172 | #define IPV6_DROP_MEMBERSHIP 21
| ^~~~~~~~~~~~~~~~~~~~
/usr/include/bits/in.h:234:10: note: this is the location of the previous definition
234 | # define IPV6_DROP_MEMBERSHIP IPV6_LEAVE_GROUP
| ^~~~~~~~~~~~~~~~~~~~
Compilers don't complain about redefinition if the defines
are identical, but here we have the kernel using the literal
value, and glibc using an indirection (defining to a name
of another define, with the same numerical value).
Problem is, the commit in question hid all the IPV6 socket
options, and glibc has a pretty sparse list. For instance
it lacks Flow Label related options. Willem called this out
in commit 3fb321fde2 ("selftests/net: ipv6 flowlabel"):
/* uapi/glibc weirdness may leave this undefined */
#ifndef IPV6_FLOWINFO
#define IPV6_FLOWINFO 11
#endif
More interestingly some applications (socat) use
a #ifdef IPV6_FLOWINFO to gate compilation of thier
rudimentary flow label support. (For added confusion
socat misspells it as IPV4_FLOWINFO in some places.)
Hide only the two defines we know glibc has a problem
with. If we discover more warnings we can hide more
but we should avoid covering the entire block of
defines for "IPV6 socket options".
Link: https://patch.msgid.link/20250609143933.1654417-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
31557b3487