[ovs-discuss] custom field in OVS flow rules

Fri Feb 10 11:29:50 UTC 2017

Dear Ben,

Thanks for your answer again.

I would go for the datapath modification. I found a similar commit for 
CT_MARK added to the datapath, i.e., 
https://github.com/openvswitch/ovs/commit/372ce9737d2bca509f9717672d95d08b6978f4a3

I mostly followed the description of the commit, however did not go 
deeply in the source-code of OVS as a whole. In this commit, I don't see 
modifications to lib/odp-util.c. I suspect that odp-util.c is a place, 
in which OVS sends the key from user-space to kernel-space? Is that 
correct? So in order to make datapath modifications operating, I guess 
that I need to mirror all the modification for CT_MARK in odp-util.c too?

Best regards,

Thx in advance for your help,

Eryk Schiller

On 02/09/2017 07:38 PM, Ben Pfaff wrote:
> To add support for a new field to the datapath, I'd look for another
> commit that does that and use it as a template.
>
> To make every packet go to userspace, the most general way is to make
> odp_flow_key_to_flow() return ODP_FIT_TOO_LITTLE for flows that should
> have the field.  For example, if your new field is present in every
> packet, then return ODP_FIT_TOO_LITTLE for every packet; if your new
> field is present in every TCP packet, then it's better to just return
> ODP_FIT_TOO_LITTLE for TCP packets.
>
> As an alternative you can add one of SLOW_* bits to ctx->xout->slow
> during flow translation, look around ofproto-dpif-xlate.c for examples.
>
> On Thu, Feb 09, 2017 at 06:12:01PM +0100, Eryk Schiller wrote:
>> Dear Ben,
>>
>> Yes, done. Thx.
>>
>> Another question; it seems to be that only the first packet of the flow is
>> appropriately matched through my user-space rule, while the rest are pretty
>> much ignored. Is there any manual about extending the kernel datapath to
>> appropriately cache my field?
>>
>> I think that for the moment, I could also live without the cache. Is there
>> any way to switch it off so that all packets (for example for a certain
>> flow) always go through ovs-vswitchd?
>>
>> Best regards,
>>
>> Eryk Schiller
>>
>>
>> Quoting Ben Pfaff <blp at ovn.org>:
>>
>>> On Wed, Feb 08, 2017 at 10:29:29PM +0100, Eryk Schiller wrote:
>>>> Dear all,
>>>>
>>>> I am writing this post, because I saw a discussion from the beginning of
>>>> 2016 about the implementation of an additional matching field of UDP in OVS.
>>>> Maybe you can help with a similar implementation.
>>>>
>>>> The discussion is here,
>>>>
>>>> https://mail.openvswitch.org/pipermail/ovs-discuss/2016-April/040894.html
>>>>
>>>> and I found another similar patch implementing some IGMP functionality here.
>>>>
>>>> https://patchwork.ozlabs.org/patch/555337/
>>>>
>>>> I went through the FAQ, discussion, and the aforementioned patch, and
>>>> implemented a new custom user-space matching rule.
>>>>
>>>> However, when I add my field to flow rules, i.e.,
>>>>
>>>> ovs-ofctl --verbose -O OpenFlow15 add-flow ovs-br
>>>> in_port=4,ip,udp,my_field=0x6,action=normal
>>>> 2017-02-08T20:42:13Z|00001|hmap|DBG|lib/shash.c:112: 7 nodes in bucket (64
>>>> nodes, 32 buckets)
>>>> 2017-02-08T20:42:13Z|00002|hmap|DBG|lib/shash.c:112: 6 nodes in bucket (128
>>>> nodes, 64 buckets)
>>>> 2017-02-08T20:42:13Z|00003|hmap|DBG|lib/shash.c:112: 7 nodes in bucket (128
>>>> nodes, 64 buckets)
>>>> 2017-02-08T20:42:13Z|00004|hmap|DBG|lib/shash.c:112: 7 nodes in bucket (128
>>>> nodes, 64 buckets)
>>>> 2017-02-08T20:42:13Z|00005|stream_unix|DBG|/var/run/openvswitch/ovs-br:
>>>> connection failed (No such file or directory)
>>>> 2017-02-08T20:42:13Z|00006|ofctl|DBG|connecting to
>>>> unix:/var/run/openvswitch/ovs-br.mgmt
>>>> 2017-02-08T20:42:13Z|00007|hmap|DBG|lib/ofp-msgs.c:1143: 6 nodes in bucket
>>>> (128 nodes, 64 buckets)
>>>> 2017-02-08T20:42:13Z|00008|hmap|DBG|lib/ofp-msgs.c:1143: 6 nodes in bucket
>>>> (256 nodes, 128 buckets)
>>>> 2017-02-08T20:42:13Z|00009|hmap|DBG|lib/ofp-msgs.c:1143: 7 nodes in bucket
>>>> (512 nodes, 256 buckets)
>>>> 2017-02-08T20:42:13Z|00010|hmap|DBG|lib/ofp-msgs.c:1143: 8 nodes in bucket
>>>> (512 nodes, 256 buckets)
>>>> 2017-02-08T20:42:13Z|00011|hmap|DBG|lib/ofp-msgs.c:1143: 6 nodes in bucket
>>>> (512 nodes, 256 buckets)
>>>> 2017-02-08T20:42:13Z|00012|hmap|DBG|lib/ofp-msgs.c:1143: 7 nodes in bucket
>>>> (512 nodes, 256 buckets)
>>>> 2017-02-08T20:42:13Z|00013|vconn|DBG|unix:/var/run/openvswitch/ovs-br.mgmt:
>>>> sent (Success): OFPT_HELLO (OF1.5) (xid=0x1):
>>>> version bitmap: 0x06
>>>> 2017-02-08T20:42:13Z|00014|vconn|DBG|unix:/var/run/openvswitch/ovs-br.mgmt:
>>>> received: OFPT_HELLO (OF1.5) (xid=0x39):
>>>> version bitmap: 0x01, 0x02, 0x03, 0x04, 0x05, 0x06
>>>> 2017-02-08T20:42:13Z|00015|vconn|DBG|unix:/var/run/openvswitch/ovs-br.mgmt:
>>>> negotiated OpenFlow version 0x06 (we support version 0x06, peer supports
>>>> version 0x06 and earlier)
>>>> 2017-02-08T20:42:13Z|00016|vconn|DBG|unix:/var/run/openvswitch/ovs-br.mgmt:
>>>> sent (Success): OFPT_FLOW_MOD (OF1.5) (xid=0x2): ADD *udp,in_port=4*
>>>> actions=NORMAL
>>>> 2017-02-08T20:42:13Z|00017|vconn|DBG|unix:/var/run/openvswitch/ovs-br.mgmt:
>>>> sent (Success): OFPT_BARRIER_REQUEST (OF1.5) (xid=0x3):
>>>> 2017-02-08T20:42:13Z|00018|poll_loop|DBG|wakeup due to 0-ms timeout
>>>> 2017-02-08T20:42:13Z|00019|poll_loop|DBG|wakeup due to [POLLIN] on fd 4
>>>> (<->/var/run/openvswitch/ovs-br.mgmt) at lib/stream-fd.c:155
>>>> 2017-02-08T20:42:13Z|00020|vconn|DBG|unix:/var/run/openvswitch/ovs-br.mgmt:
>>>> received: OFPT_BARRIER_REPLY (OF1.5) (xid=0x3):
>>>>
>>>> There is only an ADD for udp,in_port=4; so my_field seems to be ignored, but
>>>> surprisingly overall the switch does what I want. Moreover, dump-flows does
>>>> not recognize this my_field properly either.
>>>>
>>>> The question is what is the proper way to include custom my_field in OF
>>>> messages so that I can use it with ovs-ofctl add-flow and ovs-ofctl
>>>> dump-flows? Is there any additional answer to that in FAQ?
>>> It sounds like your new field just isn't being printed as part of
>>> formatting a match.  Make sure that you added it to match_format() in
>>> lib/match.c.
>>
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-- 
Dr. Eryk Schiller
Communication and Distributed Systems
Institut für Informatik
Universität Bern
Neubrückstrasse 10
CH-3012 Bern
tel: +41 (0) 31 511 26 33