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


From: Anthony Liguori
Subject: Re: [Qemu-devel] Re: [PATCH] networking using libpcap
Date: Fri, 25 Jul 2008 15:51:12 -0500
User-agent: Thunderbird 2.0.0.14 (X11/20080501)

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







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