[ovs-discuss] check_pkt_larger precision

[Numan Siddique]

On Fri, May 29, 2020 at 3:41 PM Miroslav Kubiczek <
miroslav.kubiczek at adaptivemobile.com> wrote:

>
> On 29. 05. 20 11:29, Numan Siddique wrote:
>
> On Fri, May 29, 2020 at 2:25 PM Miroslav Kubiczek <
> miroslav.kubiczek at adaptivemobile.com> wrote:
>
>> Hi,
>>
>> I have finally implemented flows with check_pkt_larger action. Partial flow dump is here:
>>
>> table=0, priority=100 actions=check_pkt_larger(60)->NXM_NX_REG0[0],resubmit(,1)
>> table=1, priority=1000,reg0=0x1 actions=resubmit(,2)
>> table=1, priority=100,reg0=0 actions=resubmit(,3)
>>
>> I run a test which sends UDP packets (with VLAN) with size: 58, 59, 62, 63 and 69 in a loop. Only the packet with 69 match the action (1st line in table=1).
>>
>> In 2nd test I set check_pkt_larger just by one byte less to 59 and then all the above packets match. So the precision seems to be rounded to 8 bytes or something like that.
>> Can this be fixed to be more precise ideally to exact 1 byte?
>>
>>
> Can you try without VLAN and see the accuracy ?
>
> I tried without VLAN, it's not accurate.
>

This is how the pkt length comparison is done

in vswitchd -
https://github.com/openvswitch/ovs/blob/master/ofproto/ofproto-dpif-xlate.c#L6265
in kernel datapath -
https://kernel.googlesource.com/pub/scm/linux/kernel/git/torvalds/linux/+/refs/heads/master/net/openvswitch/actions.c#1183

Thanks
Numan


>
>

> man ovs-actions for check_pkt_larger says
>
> ****
> Syntax:
>        check_pkt_larger(pkt_len)->dst
>
>        Checks if the packet is larger than the specified length in
> pkt_len. If so, stores 1 in dst, which should be a 1-bit field; if not,
> stores 0.
>
>        The packet length to check againt the argument pkt_len includes the
> L2 header and L2 payload of the packet, but not the VLAN tag (if present).
>
>        Examples:
>               ·      check_pkt_larger(1500)->reg0[0]
>               ·      check_pkt_larger(8000)->reg9[10]
>
> ******
>
> Thanks
> Numan
>
> Thanks,
>> Miro
>>
>>
>>
>>
>> _______________________________________________
> discuss mailing list
> discuss at openvswitch.org
> https://mail.openvswitch.org/mailman/listinfo/ovs-discuss
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.openvswitch.org/pipermail/ovs-discuss/attachments/20200529/c11d140b/attachment.html>