[ovs-dev] [PATCH 23/27] ovn-trace: Add some basic tracing for ct_snat and ct_dnat actions.
Mickey Spiegel
mickeys.dev at gmail.com
Tue May 2 18:33:27 UTC 2017
One minor nit and one real comment below.
On Tue, May 2, 2017 at 11:07 AM, Ben Pfaff <blp at ovn.org> wrote:
> On Mon, May 01, 2017 at 05:50:57PM -0700, Mickey Spiegel wrote:
> > On Mon, May 1, 2017 at 5:12 PM, Ben Pfaff <blp at ovn.org> wrote:
> >
> > > On Mon, May 01, 2017 at 03:39:32PM -0700, Mickey Spiegel wrote:
> > > > On Sun, Apr 30, 2017 at 4:22 PM, Ben Pfaff <blp at ovn.org> wrote:
> > > >
> > > > > Without this support, ovn-trace is not very useful with OpenStack,
> > > which
> > > > > uses connection tracking extensively.
> > > > >
> > > >
> > > > I scanned the patch set briefly, not what I would call a full review
> but
> > > > quick sanity checking. The only issue that I saw is described inline
> > > below.
> > >
> > > Thanks!
> > >
> > > > > + struct ovntrace_node *node = ovntrace_node_append(
> > > > > + super, OVNTRACE_NODE_TRANSFORMATION, "%s", ds_cstr(&s));
> > > > > + ds_destroy(&s);
> > > > > +
> > > > > + /* Trace the actions in the next table. */
> > > > > + trace__(dp, &ct_flow, ct_nat->ltable, pipeline, &node->subs);
> > > > >
> > > >
> > > > Since OpenStack uses NAT on distributed routers, moving on to the
> next
> > > > table is the right thing to do.
> > > >
> > > > However, in case gateway routers are used, ct_snat without an IP
> address
> > > > does not do recirc.
> > > > Lines 832 to 842 of ovn/lib/actions.c:
> > > >
> > > > } else if (snat && ep->is_gateway_router) {
> > > > /* For performance reasons, we try to prevent additional
> > > > * recirculations. ct_snat which is used in a gateway router
> > > > * does not need a recirculation. ct_snat(IP) does need a
> > > > * recirculation. ct_snat in a distributed router needs
> > > > * recirculation regardless of whether an IP address is
> > > > * specified.
> > > > * XXX Should we consider a method to let the actions specify
> > > > * whether an action needs recirculation if there are more
> use
> > > > * cases?. */
> > > > ct->recirc_table = NX_CT_RECIRC_NONE;
> > > >
> > > > Lines 4548, 4549 of ovn/northd/ovn-northd.c for a gateway router:
> > > >
> > > > ovn_lflow_add(lflows, od, S_ROUTER_IN_UNSNAT, 90,
> > > > ds_cstr(&match), "ct_snat; next;");
> > > >
> > > > The corresponding lines 4565, 4566 of ovn/northd/ovn-northd.c for a
> > > > distributed router:
> > > >
> > > > ovn_lflow_add(lflows, od, S_ROUTER_IN_UNSNAT,
> 100,
> > > > ds_cstr(&match), "ct_snat;");
> > > >
> > > > I think with this code you would be seeing double on a gateway
> router,
> > > > since both "ct_snat" and "next" would trace the actions in the next
> > > table.
> > >
> > > Oh, that's a good point.
> > >
> > > From lflow.c, a given router is a gateway router if its datapath is
> > > present on the local hypervisor and it has a local L3 gateway:
> > >
> > > static bool
> > > is_gateway_router(const struct sbrec_datapath_binding *ldp,
> > > const struct hmap *local_datapaths)
> > > {
> > > struct local_datapath *ld =
> > > get_local_datapath(local_datapaths, ldp->tunnel_key);
> > > return ld ? ld->has_local_l3gateway : false;
> > > }
> > >
> > > Therefore, this is another bit of context that ovn-trace would need to
> > > be provided via command-line options. I guess it would have to be
> > > something like "--gateway-router no,yes" to indicate, for example, that
> > > the first snat is not for a gateway router and that the second one is
> > > (or whatever). And I'd tend to assume that the default is "no" since
> > > that makes the OpenStack case work OK. Mickey and Guru, does this
> > > concept and syntax make sense? If not, can you suggest a way?
> > >
> >
> > Two ways to figure out if a router is a gateway router or not:
> >
> > 1. If you have access to nb, if the logical router has options:chassis
> then
> > it is a gateway router.
> > 2. From sb, while processing read_ports in ovn/utilities/ovn-trace.c, any
> > ports with type "l3gateway" on a datapath representing a router indicate
> > that the router is a gateway router. That is more or less what
> > ovn-controller does in "add_local_datapath" in ovn/controller/binding.c
> to
> > set "has_local_l3gateway", which ends up triggering no recirc in
> > ovn/lib/actions.c.
> >
> > The next question is whether a specific gateway router should be treated
> as
> > local. Since ovn-trace has no knowledge of topology and hypervisors, it
> > seems like the consistent approach would be to treat all gateway routers
> as
> > local for the purposes of ovn-trace.
>
> OK, how about folding in something like this?
>
> --8<--------------------------cut here-------------------------->8--
>
> diff --git a/ovn/utilities/ovn-trace.c b/ovn/utilities/ovn-trace.c
> index 4346fb39268a..638c21317f85 100644
> --- a/ovn/utilities/ovn-trace.c
> +++ b/ovn/utilities/ovn-trace.c
> @@ -346,6 +346,8 @@ struct ovntrace_datapath {
> size_t n_flows, allocated_flows;
>
> struct hmap mac_bindings; /* Contains "struct
> ovntrace_mac_binding"s. */
> +
> + bool has_local_l3gateway;
> };
>
> struct ovntrace_port {
> @@ -570,6 +572,9 @@ read_ports(void)
> port->peer->peer = port;
> }
> }
> + } else if (!strcmp(sbpb->type, "l3gateway")) {
> + /* Treat all gateways are local for our purposes. */
>
Minor nit: Treat all gateways as local for our purposes.
> + dp->has_local_l3gateway = true;
> }
> }
>
> @@ -1515,6 +1520,10 @@ execute_ct_nat(const struct ovnact_ct_nat *ct_nat,
> enum ovnact_pipeline pipeline, struct ovs_list *super)
> {
> bool is_dst = ct_nat->ovnact.type == OVNACT_CT_DNAT;
> + if (!is_dst && dp->has_local_l3gateway) {
> + /* ct_snat has no visible effect in a gateway router. */
> + return;
> + }
>
If an IP address is specified with ct_snat, then you want to replace the
address, and even on a gateway router it does trigger recirc.
Instead of this change, near the bottom, something like the following:
if (is_dst || ct_nat->ip || !dp->has_local_l3gateway) {
/* Trace the actions in the next table, except for ct_snat
* with no IP on a gateway router since there is no recirc
* in that case. */
trace__(dp, &ct_flow, ct_nat->ltable, pipeline, &node->subs);
}
Mickey
const char *direction = is_dst ? "dst" : "src";
>
> /* Make a sub-node for attaching the next table,
>
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