On Sat, Feb 10, 2018 at 09:03:10PM +1000, David Gwynne wrote:
> 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:
>
Not a fan of this since this is yet another special hack but I see why you
need it and how hard it is to fix it properly.
Grumbling ok claudio@
> 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;
>
--
:wq Claudio
