On Mon, Sep 02, 2024 at 10:14:34AM GMT, Eelco Chaudron via discuss wrote:
> Hi,
>
> I’m not an expert in this area, but I can see the metadata is explicitly
> cleared when traffic goes over a patch port.
>
> https://github.com/openvswitch/ovs/blob/0051785f00c52cbbc2897989a454a5512e82dce0/ofproto/ofproto-dpif-xlate.c#L4131
>
> If I go over the Git history, I can see this has always been the case since
> the introduction in commit 0a740f48293e.
>
> It also explicitly mentions this:
>
> /* If 'struct flow' gets additional metadata, we'll need to zero it out
> * before traversing a patch port. */
>
> So I assume the documentation might be off, or the commit was wrong (and
> it’s a bug), or there is another reason. Maybe Ilya or others know, as this
> was done 12 years ago :)
My 2 cents:
The documentation says regarding REGISTER fields:
"
These fields give an OpenFlow switch space for temporary storage
while the pipeline is running. Whereas metadata fields can have a
meaningful initial value and can persist across some hops across
OpenFlow switches, registers are always initially 0 and their
values never persist across inter-switch hops (not even across
patch ports).
"
I think the documentation refers to METADATA Fields, not the REGISTER
field that is (very confusingly) called "metadata". IIUC, it refers to
the following fields:
in_port
in_port_oxm
skb_priority
pkt_mark
actset_output
packet_type
From these, the only field that is treated specially when a packet
traverses a patch port to another bridge is "in_port" that is set to
such patch port.
Thanks.
Adrián
>
> Cheers,
>
> Eelco
>
>
> On 30 Aug 2024, at 4:27, 征途 via discuss wrote:
>
> > hello，In the ovs fields documentation, it says that metadata can retain
> > values across the ovs bridge
> >
> >
> > https://man7.org/linux/man-pages/man7/ovs-fields.7.html#METADATA_FIELDS
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > But in my tests, it doesn't seem to retain the value, can you help us to
> > answer the design in the first place?
> > Does metadata support retention of values across the ovs bridge or
> > not？thanks.
>
> > _______________________________________________
> > discuss mailing list
> > disc...@openvswitch.org
> > https://mail.openvswitch.org/mailman/listinfo/ovs-discuss
> _______________________________________________
> discuss mailing list
> disc...@openvswitch.org
> https://mail.openvswitch.org/mailman/listinfo/ovs-discuss
_______________________________________________
discuss mailing list
disc...@openvswitch.org
https://mail.openvswitch.org/mailman/listinfo/ovs-discuss
