problem with ng_device as tun replacement

[Tomas Svensson]

Julian Elischer wrote:
> Tomas Svensson wrote:
>> Hi,
>>
>> I am trying to replace the tun interface using netgraph by linking 
>> ng_device and ng_iface:
>>
>> ngctl mkpeer iface dummy inet
>> ngctl mkpeer ng0: device inet inet
>>
>> then I try to use it as a drop-in replacement for tun, but it doesn't 
>> really work:
>>
>> 1. If I send an IP packet through /dev/ngd0 (after doing a normal 
>> open()), the packet doesn't get sent until I write a second packet to 
>> the device.
>
> Do you know it the ng-device device is hanging onto it, or the 
> ng_iface device is getting it  but not passing it on?
>
> If you don't know, you can put a 'tee' node between them
> and use nghook(8) to see when the packet is passed between the nodes.
>
Thanks, I checked with tee and nghook(8) and found the follwing two cases:

1. Packets are arriving from the ng_iface (ng0) via the hook to 
ng_device (dev/ngd0), but the packets are just queuing up and the 
descriptor that opened /dev/ngd0 is not marked as readable until there 
is a number of packets queued.

2. A packet first arrives on /dev/ngd0 and is sent via the hook to ng0. 
A response packet is later arriving on the interface and is sent back to 
the device via the hook. Now the packet is stuck. Yet another packet 
arrives on /dev/ngd0 which makes it let go of the first packet (the 
first packet is sent out /dev/ngd0 and the new packet is sent via the 
hook to ng0).

I send normal ICMP echo packets and the code works fine with tun(4).

-Tomas