A netgraph question.

Julian Elischer julian at elischer.org
Sat Nov 1 19:14:33 PDT 2008

Joe Pellegrino wrote:
> On Sat, 1 Nov 2008, Julian Elischer wrote:
>> I'll try answer your questions..
>> Hooks are created on demand..
>> you need to send a 'connect' or 'mkpeer' message to the node(s)
>> on which you want t script level, you just use the ngctl program
>> to do it for you.
>> Hooks are always made in pairs. so you need two nodes to connect.
>> The mkpeer message does this for you, and creates a new node and 
>> connects them together by two hooks of the names you specify.
>> Have you looked at the sample netgraph scripts in 
>> /usr/share/examples/netgraph?
> Yep, I've looked at those but if I recall they are all scripts. I am 
> looking for some C or C++ example. Basically on the userland side I have 
> something like:
> #include <..>
> #include <netgraph/ng_socket.h>
> int main () {
>   int s1 = socket (PF_NETGRAPH, SOCK_DGRAM, NG_CONTROL)
>   int s2 = socket (PF_NETGRAPH, SOCK_DGRAM, NG_DATA)
>   bind(...);
> }
> This gives me a node with a name, set with bind, of type socket and no 
> hooks.
> The kernel module I don't have any netgraph code yet but I figure it 
> will involve a set of calls similar to the userland program. So if I 
> want to interact with the socket the userland program created, what kind 
> of node do I create in the module? Another ng_socket or a ng_ksocket or 
> something different. Then how do I go about connecting the two hooks?
>>> Of course I realize that I proabably need to create a node on the 
>>> kernel side so which type of netgraph node would be suggested? How is 
>>> it created and then hooked to the ng_socket? 
>> for fun you could use the ng_echo node type which would send 
>> everything you want back to you..
>> Alternatively when you kldload the ng-ether node type, then all the 
>> ethernets will grow nodes to match them so you can connect to them 
>> directly.
>> You could connect an ng_bpf (packet filter) node to the ng_ether node
>> and pass specific packets only on to the socket.
> I'll look into this for the other half of what I am playing with. I 
> looked at bpf by itself and it seemed to me it made a copy of the 
> packet, with the original continuing up the stack rather than diverting 
> the packet. But I am getting ahead of myself. I'd like to get the 
> userland <-> module part together first. :) And all the example code are 
> scripts. Am I missing someting?

have you done man 3 netgraph to look at the netgraph management library?

for example programs, see:
/usr/ports/net/mpd  (you'll need to download the sources with "make")

>>> pages and can't seem to find a lot of good documentation or example 
>>> code so I am hoping to get some pointers here. BTW If this is the 
>>> wrong list please directly to the right place to ask. Thanks in advance.
>> not sure what netlink does..
>> (will look on google :-)
> Thanks for your help, there is a reasonable entry in the wiki about it.
> ---jdp

More information about the freebsd-net mailing list