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Date: Tue, 28 Oct 2008 15:22:35 +0100
From: Gerd Hoffmann <kraxel@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 2/4] sockets: helper functions for qemu.
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To: "Daniel P. Berrange" <berrange@redhat.com>
Cc: qemu-devel@nongnu.org

Daniel P. Berrange wrote:
>> +    memset(&ai,0, sizeof(ai));
>> +    ai.ai_flags = AI_PASSIVE;
> 
> You should also set AI_ADDRCONFIG here. This ensure that it only
> returns IPv6 addresses if a network interface actally has IPv6
> enabled. So if someone's disabled IPv6 on a machine, and DNS still
> has IPv6 addrs, AI_ADDRCONFIG will stop QEMU pointlessly attempting
> to create IPv6 sockets that won't do anything

Done.

>> +        if (e->ai_family == PF_INET6) {
>> +            if (default_family == PF_INET6)
>> +                setsockopt(slisten,IPPROTO_IPV6,IPV6_V6ONLY,&on,sizeof(on));
>> +            else
>> +                setsockopt(slisten,IPPROTO_IPV6,IPV6_V6ONLY,&off,sizeof(off));
>> +        }

> One small problem here - for a server you need to expect more than one
> socket will be required. This is because some operating systems require
> you to bind to IPv4 and IPv6 sockets separately.

Sure?  I've googled a bit on this issue, looked what apache does here.
I've figured this can be changed per socket, with a system-wide default
configurable via sysctl (and different OSes have different default
configs here).

The setsockopt code snippet quoted above should take care about that
issue and turn off the v6only option for the socket (unless the user
explicitly asked for IPv6 using the '-ipv6' command line option).

> So we really need an array of server sockets, and attempt to
> bind to all addresses returned by getaddrinfo().

I'm trying to get around that if possible ...

> There's more info on this here
> 
>   http://people.redhat.com/drepper/userapi-ipv6.html

Hmm, IPV6_V6ONLY not mentioned there ...

>> +    memset(&ai,0, sizeof(ai));
>> +    ai.ai_flags = AI_CANONNAME;
> 
> This also needs AI_ADDRCONFIG set

Done.

cheers,
  Gerd