Subject: Re: [PATCH net-next v7] openvswitch: enable NSH support

From: "Yang, Yi" <[email-masked]>
Date: Tue, 5 Sep 2017 13:51:45 +0800

On Mon, Sep 04, 2017 at 08:57:44PM +0800, Jiri Benc wrote:
> On Mon, 4 Sep 2017 20:09:07 +0800, Yang, Yi wrote:
> > So we must do many changes if we want to break this assumption.
> 
> We may do as many changes as we want to. This is uAPI we're talking
> about and we need to get it right since the beginning. Sure, it may
> mean that some user space programs need some changes in order to make
> use of the new features. That happens every day.
> 
> I also don't understand where's the problem. It's very easy to check
> for NLA_F_NESTED and generically act based on that in the function you
> quoted. Just call a different function than format_odp_key_attr to
> handle ovs_nsh_key_attr attributes in case the nested flag is set and
> the attribute is OVS_KEY_ATTR_NSH and you're done. You'll need such
> function anyway, it's not much different code size wise to call it from
> format_odp_key_attr or from format_odp_action.

But if we follow your way, how does nla_for_each_nested handle such
pattern?

attribute1
attribute1_mask
attribute2
attribute2_mask
attribute3
attribute3_mask

I don't think this can increase performance and readability.

In current way, we just call nla_for_each_nested twice

one is for

attribute1
attribute2
attribute3

another is for

attribute1_mask
attribute2_mask
attribute3_mask

if we use one function to handle both attributes and masks, I can't
see any substantial difference between two ways as far as the
performance is concerned.

So my proposal is we needn't introduce special handling case for
OVS_KEY_ATTR_NSH in OVS_ACTION_ATTR_SET_MASKED, that will open Pandora's
box.

If we consider OVS_KEY_ATTR_NSH as a big attribute, current way is
precisely following current design pattern

attribute
mask

>  Jiri