Re: [Qemu-devel] Re: [PATCH] networking using libpcap

[Anthony Liguori <anthony@codemonkey.ws>]

Jung-uk Kim wrote:
> On Friday 18 July 2008 12:12 pm, Sebastian Herbszt wrote:
>
> I simplified FreeBSD ports patch with the above patch:
>
> http://people.freebsd.org/~jkim/qemu-devel-20080620_1-pcap.diff
>   

I spent some time with this patch looking to merge it.  It seems to have 
decent performance and is very easy to use.  Unfortunately, I ran into 
the following:

1) If I specify -net pcap,ifname=eth0 -net nic,model=rtl8139, I get an 
error, whereas if I specify -net nic,model=rtl8139 -net pcap,ifname=eth0 
it works.  The reason for this is that in net_pcap_init(), you search 
the vlan to discover what the IP address is of the NIC on the vlan is.

This is a big no-no as you can have one or more NICs on a single vlan.  
Moreover, NICs can be added and removed from a vlan long after it's 
created.  The patch needs a fair bit more work to handle this proper 
(presumably building a new filter rule as NICs are added and removed 
from the vlan).

2) When using ifname=eth0, traffic doesn't work from host=>guest nor 
from guest=>host.  This seems like a major short-coming to me.  Having 
another networking option that is easy to use but doesn't work in some 
fundamental way that a user would expect seems like it's just going to 
lead to even further confusion.  This patch isn't attractive to me 
unless it works just like you were bridging to a physical interface (and 
I don't think there's anything fundamental preventing that).

If you can fix these issues, I'd be happy to merge this feature.

Regards,

Anthony Liguori

> Thanks!
>
> Jung-uk Kim
>
>
>