ipv6 packets dont have a DF bit you can set in the header, you have
to pass it as an option to ip6_output if you want that behaviour
on output. however, ip6_send makes it hard to pass ip6 options to
ip6_output because you give it an mbuf, and hope for the best in
the future.
to cope with this, im proposing we treat "dont fragment on output"
for ipv6 as a checksum flag on an mbuf. the diff below implements
this:
Index: sys/mbuf.h
===================================================================
RCS file: /cvs/src/sys/sys/mbuf.h,v
retrieving revision 1.234
diff -u -p -r1.234 mbuf.h
--- sys/mbuf.h 9 Feb 2018 02:26:33 -0000 1.234
+++ sys/mbuf.h 10 Feb 2018 09:38:40 -0000
@@ -224,12 +224,14 @@ struct mbuf {
#define M_ICMP_CSUM_OUT 0x0200 /* ICMP/ICMPv6 checksum needed
*/
#define M_ICMP_CSUM_IN_OK 0x0400 /* ICMP/ICMPv6 checksum
verified */
#define M_ICMP_CSUM_IN_BAD 0x0800 /* ICMP/ICMPv6 checksum bad */
+#define M_IPV6_DF_OUT 0x1000 /* don't fragment outgoing IPv6
*/
#ifdef _KERNEL
#define MCS_BITS \
("\20\1IPV4_CSUM_OUT\2TCP_CSUM_OUT\3UDP_CSUM_OUT\4IPV4_CSUM_IN_OK" \
"\5IPV4_CSUM_IN_BAD\6TCP_CSUM_IN_OK\7TCP_CSUM_IN_BAD\10UDP_CSUM_IN_OK" \
- "\11UDP_CSUM_IN_BAD\12ICMP_CSUM_OUT\13ICMP_CSUM_IN_OK\14ICMP_CSUM_IN_BAD")
+ "\11UDP_CSUM_IN_BAD\12ICMP_CSUM_OUT\13ICMP_CSUM_IN_OK\14ICMP_CSUM_IN_BAD" \
+ "\15IPV6_NODF_OUT")
#endif
/* mbuf types */
Index: netinet6/ip6_output.c
===================================================================
RCS file: /cvs/src/sys/netinet6/ip6_output.c,v
retrieving revision 1.232
diff -u -p -r1.232 ip6_output.c
--- netinet6/ip6_output.c 1 Sep 2017 15:05:31 -0000 1.232
+++ netinet6/ip6_output.c 10 Feb 2018 09:38:40 -0000
@@ -656,7 +656,10 @@ reroute:
*/
tlen = m->m_pkthdr.len;
- if (opt && (opt->ip6po_flags & IP6PO_DONTFRAG))
+ if (ISSET(m->m_pkthdr.csum_flags, M_IPV6_DF_OUT)) {
+ CLR(m->m_pkthdr.csum_flags, M_IPV6_DF_OUT);
+ dontfrag = 1;
+ } else if (opt && ISSET(opt->ip6po_flags, IP6PO_DONTFRAG))
dontfrag = 1;
else
dontfrag = 0;
