[ovs-discuss] Adding/Removing Flows Programmatically in C Application

Ben Warren ben at skyportsystems.com
Mon Oct 16 22:24:44 UTC 2017


Hi Tommy,

Here’s how I do it.  It’s essentially the same as what the ‘ovs-ofctl add-flow’ command does under the hood.

1. Build a string formatted as the “ovs-ofctl” command would do, for example “table=1,cookie=0xdeadbeef,in_port=1,actions=resubmit(,2)”
2. Pass this to parser_ofp_flow_mod_str().  The parser will magically parse the string in to a rich struct.
3. Pass the struct to ofputil_encode_flow_mod().  This returns a struct with a serialized OpenFlow message buffer.
4. Send this buffer on the wire either via a socket you manage yourself or let OpenVswitch do it for you.

—Ben

> On Oct 16, 2017, at 2:05 PM, Tommy Romano <tomrom95 at fb.com> wrote:
> 
> My project was previously calling system commands like ‘ovs-ofctl add-flow’ directly from C, but we would like to do this programmatically now, by calling into the openvswitch library. After looking at this for a bit and what methods I would have to call, I’ve realized this is non trivial, and I can’t find any easily exposed methods to add and delete flows. Does anyone have an example anywhere of calling into openvswitch methods directly to add/remove flows? So far the best way I can find is calling into ovn/controller/ofctrl.h:ofctrl_add_flow(…), but this will require quite a bit of legwork.
> Best,
> Tommy Romano
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