Re: [PATCH net-next 2/2] net: cls_u32: Add support for skip-sw flag to tc u32 classifier.

[David Miller]

From: "Samudrala, Sridhar" 
Date: Wed, 11 May 2016 16:44:55 -0700

> 
> On 5/11/2016 4:23 PM, David Miller wrote:
>> This is a core semantic issue, and we have to make sure all amongst us
>> that we are all comfortable with exporting the offloadability controls
>> in the way you are implementing them.
> 
> I tried to implement the semantics based on an earlier discussion
> about these flags in this
> email thread.
> http://thread.gmane.org/gmane.linux.network/401733

Most developers reading your patches will not know to go to that URL,
nor that we even had that discussion at all.

Re: [PATCH net-next 2/2] net: cls_u32: Add support for skip-sw flag to tc u32 classifier.

[Samudrala, Sridhar]

On 5/11/2016 4:23 PM, David Miller wrote:

From: Sridhar Samudrala 
Date: Mon,  9 May 2016 12:18:44 -0700


On devices that support TC U32 offloads, this flag enables a filter to be
added only to HW. skip-sw and skip-hw are mutually exclusive flags. By
default without any flags, the filter is added to both HW and SW, but no
error checks are done in case of failure to add to HW. With skip-sw,
failure to add to HW is treated as an error.

I really want you to provide a "[PATCH net-next 0/2]" header posting
explaining what this series is doing, and why.


Sure. Will submit a v2 with a header patch in a day or so after waiting 
for any other comments.




This is a core semantic issue, and we have to make sure all amongst us
that we are all comfortable with exporting the offloadability controls
in the way you are implementing them.


I tried to implement the semantics based on an earlier discussion about 
these flags in this

email thread.
http://thread.gmane.org/gmane.linux.network/401733




Also:


@@ -871,10 +889,15 @@ static int u32_change(struct net *net, struct sk_buff 
*in_skb,
return err;
}
  
+		err = u32_replace_hw_knode(tp, new, flags);

+   if (err) {
+   u32_destroy_key(tp, new, false);
+   return err;
+   }
+
u32_replace_knode(tp, tp_c, new);
tcf_unbind_filter(tp, >res);
call_rcu(>rcu, u32_delete_key_rcu);
-   u32_replace_hw_knode(tp, new, flags);
return 0;
}
  

Are you sure this reordering is OK?


I think so. This reordering is required to support skip-sw semantic of 
returning error in case of failure to add to hardware.
It doesn't break the default semantics of adding to both hw and sw as 
u32_replace_hw_knode() will not return err if skip-sw is not set.


Thanks
Sridhar

Re: [PATCH net-next 2/2] net: cls_u32: Add support for skip-sw flag to tc u32 classifier.

[David Miller]

From: Sridhar Samudrala 
Date: Mon,  9 May 2016 12:18:44 -0700

> On devices that support TC U32 offloads, this flag enables a filter to be
> added only to HW. skip-sw and skip-hw are mutually exclusive flags. By
> default without any flags, the filter is added to both HW and SW, but no
> error checks are done in case of failure to add to HW. With skip-sw,
> failure to add to HW is treated as an error.

I really want you to provide a "[PATCH net-next 0/2]" header posting
explaining what this series is doing, and why.

This is a core semantic issue, and we have to make sure all amongst us
that we are all comfortable with exporting the offloadability controls
in the way you are implementing them.

Also:

> @@ -871,10 +889,15 @@ static int u32_change(struct net *net, struct sk_buff 
> *in_skb,
>   return err;
>   }
>  
> + err = u32_replace_hw_knode(tp, new, flags);
> + if (err) {
> + u32_destroy_key(tp, new, false);
> + return err;
> + }
> +
>   u32_replace_knode(tp, tp_c, new);
>   tcf_unbind_filter(tp, >res);
>   call_rcu(>rcu, u32_delete_key_rcu);
> - u32_replace_hw_knode(tp, new, flags);
>   return 0;
>   }
>  

Are you sure this reordering is OK?