Re: checking m->m_pkthdr.csum_flags in ip_output()

[Takahiro Kambe <taca%back-street.net@localhost>]

Hi,

In message <20080415.203216.41648300.taca%back-street.net@localhost>
        on Tue, 15 Apr 2008 20:32:16 +0900 (JST),
        Takahiro Kambe <taca%back-street.net@localhost> wrote:
> Today, NetBSD 4.0_STABLE machine paniced in ip_output() when
> forwarding IPv4 multicast packet.  The packet was short (36 octets)
> UDP/IP pakcet.
...
> The kernel has DIAGNOSTIC option enabled and corresponding code
> fragments in ip_output().
> 
> #ifdef        DIAGNOSTIC
>       if ((m->m_flags & M_PKTHDR) == 0)
>               panic("ip_output: no HDR");
> 
>       if ((m->m_pkthdr.csum_flags & (M_CSUM_TCPv6|M_CSUM_UDPv6)) != 0) {
>               panic("ip_output: IPv6 checksum offload flags: %d",
>                   m->m_pkthdr.csum_flags);
>       }
> 
>       if ((m->m_pkthdr.csum_flags & (M_CSUM_TCPv4|M_CSUM_UDPv4)) ==
>           (M_CSUM_TCPv4|M_CSUM_UDPv4)) {
>               panic("ip_output: conflicting checksum offload flags: %d",
>                   m->m_pkthdr.csum_flags);
>       }
> #endif
> 
> It seems that this diagnostic code checking M_CSUM_TCPv4 and
> M_CSUM_UDPv4 are exclusive one.
I confirmed that bge(4) sets both M_CSUM_TCPv4 and M_CSUM_UDPv4 to
m->m_pkthdr.csum_flags with usual unicast IP packets.

I don't know it is bug of bge(4) or above DIAGNOSTIC is wrong or
obsolete.

-- 
Takahiro Kambe <taca%back-street.net@localhost>