Re: Net.Manager

[Vincent Bernardoff <vb@xxxxxxxxxxxxxx>]

On 22/03/2013 13:45, Haris Rotsos wrote:

> in order to create a tuntap interface you need to open an fd to a
> /dev/tapX or /dev/taunX. The device is open only while the problem is
> running and keeps the fd open. This is the case for both linux and mac.
No, in Linux you have open /dev/net/tun and use ioctl to configure the 
mode of operation, if you want it persistent or not, user/group 
ownership, etc.
> The difference is that on linux there is a tun daemon and thep tunctl
> command which can persist a tun interface without a requirement for an fd.
I did not see any "tun daemon" on my Linux whatsoever. I donât use the 
tunctl command either. Iâm using the "ip" command (ip tuntap add mode 
tap) which creates a persistent tap for me. Indeed there is no 
requirement for a fd. I made an OCaml "tunctl" command to test the 
ocaml-tuntap bindings, it is correctly replicating the behaviour of the 
"ip tuntap" command.
>     PCAP was used have macs able to attach to a tun/tap using a
>     different library (PCAP). I donât know exactly why PCAP was used for.
>
>
> Pcap is used in the unix backend in order to create a user space
> openflow switch in MacOSX. In such a setting you need to be able to have
> both tun/tap interfaces as well as ethernet network devices. In MacOSX
> there is no ethernet raw socket thing unfortunately and the best way to
> intercept traffic in such a case is through a bpf device.
>
>
>     My idea is to use ocaml-tuntap in macosx and linux the same way,
>     creating transcient interfaces and passing the fd over a unix domain
>     socket. This would work in all cases.
>
>
> In this case you won't be able to integrate an existing network
> interface to the Mirage Network stack. You need at least to consider raw
> ethernet sockets for linux, bpf for MacOSX and find some nice
> abstraction to expose this through the Manager(?) API.
Ok, just read about raw ethernet sockets. I did not know that it was 
possible, it is interesting. The possibility I was thinking about was to 
"integrate an existing network interface" in creating a tap interface 
and bridge it with the real network interface. This way you probably can 
read inbound/outbound ethernet frames. Would it be possible to do that 
on MacOSX ?
Could you please point me to some documentation on how to do that on Macs ?

Thank you very much for the explanation.

Cheers,

Vincent