Re: [advanced API] how to get the destination address for IPV6_RECVPATHMTU

[Jun-ichiro itojun Hagino]

>   >>> I've implemented the IPV6_RECVPATHMTU option adopting #3 approach. I
>   >>> defined a new structure "ip6_mtuinfo" as ancillary data item for
>   >>> IPV6_PATHMTU as follows:
>   >>> struct ip6_mtuinfo {
>   >>> u_int32_t ip6mtu_mtu;
>   >>> struct sockaddr_in6 ip6mtu_dst;
>   >>> };
>   >> How do you think about alignment?
>   >Currently, I only consider 32-bit alignment, but I'm open to hear
>   >others' opinions.
>       as this structure is host-local (will not appear on wire) there's no
>       serious issue with alignment, I believe.
>=> I disagree, I'd like to be able to defined struct in6_addr as a pair
>of 64 bit integers one day (:-)!

        I don't understand what you are saying, at all.
        ip6mtu_dst will be aligned to the alignment whatever necessary for us,
        depending on how your compiler aligns it.  sockaddr_in6 includes
        struct in6_addr (sin6_addr), and if you declare in6_addr like:
                struct in6_addr {
                        union {
                                uint8_t foo8[16];
                                uint16_t foo16[8];
                                uint32_t foo32[4];
                                uint64_t foo32[2];
                        } foo;
                };
        ip6mtu_dst.sin6_addr should be aligned to 64bit boundary.

>       ip6mtu_dst will be aligned to whatever look natural to the machine
>       based on sockaddr_in6 declaration.
>=> please do something similar to in6_pktinfo...

itojun
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