RTL8139 NIC driver: how to test ?

[karuon]

Hi !

I am currently trying to develop a network stack for my OS and I need a bit of your help. I started by writing a driver for RTL8139 network card. The problem is I have no idea how to check it works properly.

Actually, I did try to send some packets from my OS : I set up a tap device, specified it to Qemu (the VM I use for my tests) and tried to send ethernet frames from my OS. While listening on my tap with tcpdump, the sent packets seemed to be detected.

But now I'd like to check whether my NIC driver can process received packets. I unsuccessfully tried the following: associate IPv4 address 192.168.1.166 (which was unused, I did check) to my tap, ping it. The ping responded but no frame was received by my OS. However, I'm not sure this test is appropriate.

I'd like to be able to test my driver before developping the upper layers of my network stack. What do you suggest ?

Thanks in advance.

[bluemoon]

Did you get IRQ triggered when you ping your OS with multi-cast packets?
If not, you may want to double check your qemu parameters and host's interface setting, you should get random junk packets with valid bridge mode.
I'm using this on linux:

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-netdev type=tap,id=br0 -device rtl8139,netdev=br0

Once you start getting IRQ, make sure you initialize the RX buffer with physical address.

[karuon]

No, ping multicast does not work.

However, I have tried to create a bridge ; I added tap0 (my tap interface) and enp3s0 (my Ethernet interfavce) to this bridge and finally my driver seemed to receive packets. But it would be interested to test your method also: what do you put in your qemu-ifup script ?

Still, ping does not work and I don't understand why.

[bluemoon]

My if interface is configured with:

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auto br0
iface br0 inet dhcp
        bridge_ports eth0
        bridge_stp off
        bridge_fd 0
        bridge_maxwait 0

You may also read more on https://help.ubuntu.com/community/KVM/Networking.

Still, ping does not work and I don't understand why.

Do you ping to a specific unicast IP or multi-cast address? Are you sure the packet get routed to correct NIC?

[karuon]

Do you ping to a specific unicast IP or multi-cast address?

Well, first I tried to ping 192.168.1.166 and then 224.0.0.1. But pinging 224.0.0.1 gives no response (maybe because no machine in my local network supports multicast ?).

Are you sure the packet get routed to correct NIC?

Unfortunately,

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tcpdump -i tap0

displays nothing while pinging.

But I think this problem is not specifically related to Qemu. When creating a tap device (tap0) this way:

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ip tuntap add user $USER mode tap
ip address add 192.168.1.166 dev tap0
ip link set dev tap0 up

pinging 192.168.1.166 does not work according to tcpdump output. I think the problem is here. By the way, even after setting tap0 up,

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ip link show

says it is down. And no error is displayed by

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ip link set dev tap0 up

[bluemoon]

You need to specify the NIC for such multi-cast group, otherwise it might get defaults to lo0.
The other method is manually join the group with setsockopt / IP_ADD_MEMBERSHIP, but it is unnecessary in this case.

Check it here: http://www.tldp.org/HOWTO/Adv-Routing-H ... icast.html

Note that a physical router may block multicast packets to non-subscribers, but it should work for direct connected machines and emulators.

[karuon]

I've tried to specify a new route (224.0.0.0/4) using NIC tap0, but I still get nothing with tcpdump -i tap0 when I ping 224.0.0.1 for instance.