commit c9bd40daaee18cf1d9824e4a7ebaebe321e0a5a8
Author: Carlos O'Donell <carlos@redhat.com>
Date:   Tue Jun 7 04:46:37 2016 -0400
 
    Bug 20214: Fix linux/in6.h and netinet/in.h sync.
    
    In: https://sourceware.org/glibc/wiki/Synchronizing_Headers
    we explain how we synchronize our headers with Linux kernel
    headers.
    
    In order to synchronize with the Linux linux/in6.h and
    linux/ipv6.h headers we checked for their guard macros and
    then defined __USE_KERNEL_IPV6_DEFS and conditionalized code
    on this macro.
    
    In upstream kernel 56c176c9 the _UAPI prefix was stripped and
    this broke our synchronized headers again. We now need to check
    for _LINUX_IN6_H and _IPV6_H, and keep checking the old versions
    of the header guard checks for maximum backwards compatibility
    with older Linux headers (the history is actually a bit muddled
    here and it appears upstream linus kernel broke this 10 months
    *before* our fix was ever applied to glibc, but without glibc
    testing we didn't notice and distro kernels have their own
    testing to fix this).
    
    This patch fixes synchronization with linux/in6.h and
    with netinet/in.h.
 
diff --git a/sysdeps/unix/sysv/linux/bits/in.h b/sysdeps/unix/sysv/linux/bits/in.h
index 9bdadf3..4d70a6b 100644
--- a/sysdeps/unix/sysv/linux/bits/in.h
+++ b/sysdeps/unix/sysv/linux/bits/in.h
@@ -25,8 +25,14 @@
    kernel then we will not define the IPv6 IPPROTO_* defines, in6_addr (nor the
    defines), sockaddr_in6, or ipv6_mreq. Same for in6_ptkinfo or ip6_mtuinfo
    in linux/ipv6.h. The ABI used by the linux-kernel and glibc match exactly.
-   Neither the linux kernel nor glibc should break this ABI without coordination.  */
-#if defined _UAPI_LINUX_IN6_H || defined _UAPI_IPV6_H
+   Neither the linux kernel nor glibc should break this ABI without coordination.
+   In upstream kernel 56c176c9 the _UAPI prefix was stripped so we need to check
+   for _LINUX_IN6_H and _IPV6_H now, and keep checking the old versions for
+   maximum backwards compatibility.  */
+#if defined _UAPI_LINUX_IN6_H \
+    || defined _UAPI_IPV6_H \
+    || defined _LINUX_IN6_H \
+    || defined _IPV6_H
 /* This is not quite the same API since the kernel always defines s6_addr16 and
    s6_addr32. This is not a violation of POSIX since POSIX says "at least the
    following member" and that holds true.  */
@@ -209,8 +215,10 @@ struct in_pktinfo
 #define IPV6_TCLASS		67
 
 /* Obsolete synonyms for the above.  */
-#define IPV6_ADD_MEMBERSHIP	IPV6_JOIN_GROUP
-#define IPV6_DROP_MEMBERSHIP	IPV6_LEAVE_GROUP
+#if !__USE_KERNEL_IPV6_DEFS
+# define IPV6_ADD_MEMBERSHIP	IPV6_JOIN_GROUP
+# define IPV6_DROP_MEMBERSHIP	IPV6_LEAVE_GROUP
+#endif
 #define IPV6_RXHOPOPTS		IPV6_HOPOPTS
 #define IPV6_RXDSTOPTS		IPV6_DSTOPTS