[ovs-dev] Possible Regression in 'netdev: Add new "struct netdev_rx" for capturing packets from a netdev.'

Simon Horman horms at verge.net.au
Tue Jun 11 01:13:21 UTC 2013

Hi Ethan, Hi All,

I have observed what appears to be a regression caused by
796223f5bc3a4896e6398733c798390158479400 ('netdev: Add new "struct
netdev_rx" for capturing packets from a netdev.').

In my test environment I am using Open vSwitch with the user-space
datapath inside a KVM virtual machine. The virtual machine has a single
bridge with two interfaces attached, eth0 and dummy0.

dummy0 is (as its name suggests) a dummy interface.

eth0 is a virtual ethernet interface the other end of which
is a tap device in the host, tap0.

In the host tap0 is attached to a (normal linux, not Open vSwtich)
bridge and that bridge has a local IP address. I suspect that this
is not relevant other than that the host can send packets to the virtual

The problem that I see is that when Open vSwtich receives a multicast
packet, either IPv4 or IPv6, the packet seems to loop forever.

I suspect that what is happening is that Open vSwtich receives the
multicast packet, then floods it to all interfaces, however for some
reason it then receives the packet again and thus a loop is established.

It is not at all apparent to me why this problem is caused by
the patch referred to above. However, I have tested it a number of
times and feel confident that it is the case.

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