Thanks Ben. So then the flow struct, along with its members excluding
metadata, tunnel and regs propagate, correct?


2018-04-05 21:30 GMT+02:00 Ben Pfaff <b...@ovn.org>:

> compose_output_action__(), in ofproto/ofproto-dpif-xlate.c, clears
> metadata for patch port traversals in the block that begins "if
> (xport->peer)", with this code:
>
>         flow->metadata = htonll(0);
>         memset(&flow->tunnel, 0, sizeof flow->tunnel);
>         memset(flow->regs, 0, sizeof flow->regs);
>
>
> On Thu, Apr 05, 2018 at 08:52:31PM +0200, Alan Kayahan wrote:
> > That....is my question and theory :) How can I see that? Can you point me
> > to the code where such decision is taken?
> >
> > 2018-04-05 20:39 GMT+02:00 Ben Pfaff <b...@ovn.org>:
> >
> > > What metadata is propagating?
> > >
> > > On Thu, Apr 05, 2018 at 08:14:51PM +0200, Alan Kayahan wrote:
> > > > I introduced a new 32bit field in flow.h to match on. A push_header
> > > action
> > > > appends a header, which contains TLVs, to the packet and sets this
> field
> > > > for the first time. An increment action sets this field to a value
> that
> > > > resides in the first TLV, if increment action is called again, the
> field
> > > is
> > > > set to the value in the second TLV and so on.
> > > >
> > > > I have a chain of br0-br1-br2 connected via patch ports. In br0 flow
> rule
> > > > calls push_header and out to br1. In br1, the flow rule matches on
> the
> > > port
> > > > connected to br0, plus match on the 32bit field.The action for this
> rule
> > > is
> > > > increment, then out to br2. Just like br1, br2 matches on the port
> from
> > > br1
> > > > plus the match on the 32bit field for the value in the TLV.
> > > >
> > > > Everything works well until br2. But the match on the field for the
> value
> > > > in the TLV doesn't work. If I remove the match on the field at br2
> and
> > > just
> > > > use in_port and redirect the traffic to packet hex printer, I do see
> that
> > > > the value in the TLV has been set correctly at the offset of this
> 32bit
> > > > field.
> > > >
> > > > The increment action depends on the iteration of TLVs in the header
> at
> > > each
> > > > packet, therefore is at datapath and can not update the flow
> context. So
> > > if
> > > > the flow metadata is propagating (which seems to be the only
> > > explanation),
> > > > the new field is set to the old value, which is the culprit. Perhaps
> a
> > > > better approach is to create an own context just like nat, iterate
> the
> > > TLVs
> > > > and populate the context with all available values when push_header
> is
> > > > first called, then redesign the increment action so that it just
> pops the
> > > > next value from the context and emits the data-plane action.
> Eliminates
> > > > TLVs iteration per packet at the dataplane.
> > > >
> > > > But just to save the day, do you have a trick to stop this
> propagation?
> > > Or
> > > > do you think the problem might be something else?
> > > >
> > > > Thanks!
> > > >
> > > > 2018-04-05 19:41 GMT+02:00 Ben Pfaff <b...@ovn.org>:
> > > >
> > > > > On Thu, Apr 05, 2018 at 07:31:35PM +0200, Alan Kayahan wrote:
> > > > > > OVS patch ports allow the propagation of the metadata (e.g. flow
> > > context)
> > > > > > across the connected switches.
> > > > > >
> > > > > > Is there an option to disable the metadata propagation feature? I
> > > need
> > > > > this
> > > > > > for my research to benchmark certain behavior. Or patch ports
> become
> > > > > > nothing but veth pairs when this feature is disabled?
> > > > >
> > > > > Patch ports zero out most metadata.  What additional metadata do
> you
> > > > > want them to clear?
> > > > >
> > >
>
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