netdev - Re: [net-next PATCH v1 01/11] net: flow_table: create interface for hw match/action tables

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Date:	Tue, 6 Jan 2015 11:54:58 +0900
From:	Simon Horman <simon.horman@...ronome.com>
To:	John Fastabend <john.fastabend@...il.com>
Cc:	Thomas Graf <tgraf@...g.ch>, sfeldma@...il.com, jiri@...nulli.us,
	jhs@...atatu.com, netdev@...r.kernel.org, davem@...emloft.net,
	andy@...yhouse.net
Subject: Re: [net-next PATCH v1 01/11] net: flow_table: create interface for
 hw match/action tables

On Tue, Jan 06, 2015 at 11:05:14AM +0900, Simon Horman wrote:
> On Mon, Jan 05, 2015 at 05:19:26PM -0800, John Fastabend wrote:
> > On 01/05/2015 05:09 PM, Simon Horman wrote:
> > >On Mon, Jan 05, 2015 at 04:45:50PM -0800, John Fastabend wrote:
> > >>[...]
> > >>
> > >>>>>+/**
> > >>>>>+ * @struct net_flow_field_ref
> > >>>>>+ * @brief uniquely identify field as header:field tuple
> > >>>>>+ */
> > >>>>>+struct net_flow_field_ref {
> > >>>>>+    int instance;
> > >>>>>+    int header;
> > >>>>>+    int field;
> > >>>>>+    int mask_type;
> > >>>>>+    int type;
> > >>>>>+    union {    /* Are these all the required data types */
> > >>>>>+        __u8 value_u8;
> > >>>>>+        __u16 value_u16;
> > >>>>>+        __u32 value_u32;
> > >>>>>+        __u64 value_u64;
> > >>>>>+    };
> > >>>>>+    union {    /* Are these all the required data types */
> > >>>>>+        __u8 mask_u8;
> > >>>>>+        __u16 mask_u16;
> > >>>>>+        __u32 mask_u32;
> > >>>>>+        __u64 mask_u64;
> > >>>>>+    };
> > >>>>>+};
> > >>>>
> > >>>>Does it make sense to write this as follows?
> > >>>
> > >>>Yes. I'll make this update it helps make it clear value/mask pairs are
> > >>>needed.
> > >>>
> > >>>>
> > >>>>union {
> > >>>>         struct {
> > >>>>                 __u8 value_u8;
> > >>>>                 __u8 mask_u8;
> > >>>>         };
> > >>>>         struct {
> > >>>>                 __u16 value_u16;
> > >>>>                 __u16 mask_u16;
> > >>>>         };
> > >>>>         ...
> > >>>>};
> > >>
> > >>Another thought is to pull this entirely out of the structure and hide
> > >>it from the UAPI so we can add more value/mask types as needed without
> > >>having to spin versions of net_flow_field_ref. On the other hand I've
> > >>been able to fit all my fields in these types so far and I can't think
> > >>of any additions we need at the moment.
> > >
> > >FWIW, I think it would be cleaner to break both field_ref and action_args
> > >out into attributes and not expose the structures to user-space. But
> > >perhaps there is an advantage to dealing with structures directly that
> > >I am missing.
> > >
> > 
> > I  came to the same conclusion just now as well. I'm reworking it now
> > for v2.
> 
> Thanks.
> 
> BTW, I think there are a few problems with net_flow_put_flow_action().
> 
> I am not quite to the bottom of it but it seems that:
> * It loops over a->args[i] and then calls net_flow_put_act_types()
>   which performs a similar loop. This outer-loop appears to be incorrect.
> * It passes a[i].args instead of a->args[i] to net_flow_put_act_types()
> 
> I can post a fix once I've got it working to my satisfaction.
> But if you are reworking that code anyway perhaps it is easier for
> you to handle it then.

FWIW this got the current scheme working for me:

diff --git a/net/core/flow_table.c b/net/core/flow_table.c
index 5dbdc13..598afa2 100644
--- a/net/core/flow_table.c
+++ b/net/core/flow_table.c
@@ -946,7 +946,7 @@ static int net_flow_put_flow_action(struct sk_buff *skb,
 				    struct net_flow_action *a)
 {
 	struct nlattr *action, *sigs;
-	int i, err = 0;
+	int err = 0;
 
 	action = nla_nest_start(skb, NET_FLOW_ACTION);
 	if (!action)
@@ -958,21 +958,19 @@ static int net_flow_put_flow_action(struct sk_buff *skb,
 	if (!a->args)
 		goto done;
 
-	for (i = 0; a->args[i].type; i++) {
-		sigs = nla_nest_start(skb, NET_FLOW_ACTION_ATTR_SIGNATURE);
-		if (!sigs) {
-			nla_nest_cancel(skb, action);
-			return -EMSGSIZE;
-		}
+	sigs = nla_nest_start(skb, NET_FLOW_ACTION_ATTR_SIGNATURE);
+	if (!sigs) {
+		nla_nest_cancel(skb, action);
+		return -EMSGSIZE;
+	}
 
-		err = net_flow_put_act_types(skb, a[i].args);
-		if (err) {
-			nla_nest_cancel(skb, sigs);
-			nla_nest_cancel(skb, action);
-			return err;
-		}
-		nla_nest_end(skb, sigs);
+	err = net_flow_put_act_types(skb, a->args);
+	if (err) {
+		nla_nest_cancel(skb, sigs);
+		nla_nest_cancel(skb, action);
+		return err;
 	}
+	nla_nest_end(skb, sigs);
 
 done:
 	nla_nest_end(skb, action);
@@ -1103,6 +1101,7 @@ static int net_flow_get_action(struct net_flow_action *a, struct nlattr *attr)
 		}
 
 		a->args[count] = *(struct net_flow_action_arg *)nla_data(args);
+		count++;
 	}
 	return 0;
 }
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