Re: [Qemu-devel] [PATCH] net: add raw backend

[Or Gerlitz <ogerlitz@voltaire.com>]

Jamie Lokier wrote:
> No, I meant "-net pcap", whose patch is announced at
> http://lists.freebsd.org/pipermail/freebsd-emulation/2007-February/003108.html
> and found here: http://people.freebsd.org/~jkim/patch-qemu-pcap.diff I saw it mention on this list in the last few months. It sends and receives packets over a host network interface using libpcap.
okay, looking a bit on the archives I realized that the -net pcap 
backend was suggested on the qemu-devel list at least twice, on 2007 
(your pointer) and recently, e.g @ 
http://lists.gnu.org/archive/html/qemu-devel/2009-03/msg00895.html and 
the mail threads that followed from March, April and May 2009. Under 
Linux the pcap library uses a packet socket, so basically it could make 
some sense to go through libpcap and not directly to sockets, but there 
are also some disadvantages which will not less qemu implement some 
related optimizations which are not integrated into libpcap.

Now, before going into libpcap vs. packet socket, I'd be happy if you or 
Antony can help me understand the comments that with this approach guest 
<--> host communication is impossible. AFAIK, the only packet sent by 
Qemu is gratuitous ARP after migration, but it doesn't fall into guest 
<--> host communication over the NIC/vlan/back-end gang, so I don't see 
what is this traffic which is impossible with the bridge-less approach.

Also, if for some reason one need to communicate from the guest to the 
host the -net raw can instructed to run over a veth Linux interface 
couple which are connected to a bridge.

Or.