New unix backend for mirage

[Vincent Bernardoff <vb@xxxxxxxxxxxxxx>]

Hi all,

I have been working recently on refactoring the UNIX backend for Mirage.
Mainly, the modification are that now the code that handles tun/tap 
creation has been extracted in a new library ocaml-tuntap (You car 
install it with OPAM, or git://github.com/vbmithr/ocaml-tuntap).
I have refactored mirage-platform and mirage-net such that now, 
mirage-platform do not create tap interfaces directly in OS.Netif, but 
instead, there is an OS.Netif.add_vif function that takes a fd as 
parameter and that adds it as available interface for the unikernel.
Now, mirari generates a Backend module that contains the code to create 
a tap interface, and this module calls the OS.Netif.add_vif (via the 
manager). This Backend module is actually the equivalent of XenStore for 
the UNIX backend, it implements a server that listens on a UNIX domain 
socket for commands from mirari. For now only ADD_VIF is implemented, 
but PAUSE, RESUME, SUSPEND, etc.. will be implemented in the future if 
there is a need for it.
So basically, my big interrogation for now is "Why does this works 
perfectly on Linux and not on MacOS, given that the only difference is 
the tuntap creation code (but that is working, cleanly separated in 
ocaml-tuntap).
If you want to test, try the following:

Use mirage-platform, mirage-net and mirari from my repo 
(git://github.com/vbmithr/~), branch new-unix-backend2.
(Typically, you opam pin these packages before installing).

Then git clone git://github.com/mirage/mirage-skeleton
cd mirage-skeleton/basic, then

mirari configure --unix
mirari build --unix
sudo mirari run --unix

This should typically "work" under UNIX:


[vb@haramix ~/code/mirage-skeleton/basic]% sudo mirari run --unix 
                                                          [mirari] 
Using scanned config file hello.conf [mirari] Make the unikernel create 
the tap0 interface. Manager: create Manager: init done [mirari] 
Connecting to /tmp/mir-6224.sock... [mirari] Transmitted message ok. 
[backend]: Connection from mirari. [backend]: received command VIF_ADD 
[backend]: Creating tap0... plugging into tap0 with mac 
92:f0:ab:83:1a:f6.. Netif: plug tap0 Manager: plug tap0 Manager: plug 
done, to listener Manager: Interface tap0 to DHCP DHCP: waiting for 
first offer DHCP: start discovery Sending DHCP broadcast len 552

But not work under MacOS: stuck at [backend]: Creating tap0...

Thanks to anybody that can have a look at that (preferably people with 
macs).
Thanks in advance,

Vincent