netdev - Re: [PATCH 2/2] netlink: add ethernet address policy types

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Date:   Thu, 13 Sep 2018 22:39:52 +0200
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc:     Johannes Berg <johannes@...solutions.net>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 2/2] netlink: add ethernet address policy types

On Thu, Sep 13, 2018 at 04:41:16PM -0300, Marcelo Ricardo Leitner wrote:
> On Thu, Sep 13, 2018 at 02:16:06PM +0200, Johannes Berg wrote:
> > On Thu, 2018-09-13 at 14:12 +0200, Michal Kubecek wrote:
> > > On Thu, Sep 13, 2018 at 02:02:53PM +0200, Johannes Berg wrote:
> > > > On Thu, 2018-09-13 at 13:58 +0200, Michal Kubecek wrote:
> > > > 
> > > > > The code looks correct to me but I have some doubts. Having a special
> > > > > policy for MAC addresses may lead to adding one for IPv4 address (maybe
> > > > > not, we can use NLA_U32 for them), IPv6 addresses and other data types
> > > > > with fixed length. Wouldn't it be more helpful to add a variant of
> > > > > NLA_BINARY (NLA_BINARY_EXACT?) which would fail/warn if attribute length
> > > > > isn't equal to .len?
> > > > 
> > > > Yeah, I guess we could do that, and then
> > > > 
> > > > #define NLA_ETH_ADDR .len = ETH_ALEN, .type = NLA_BINARY_EXACT
> > > > #define NLA_IP6_ADDR .len = 16, .type = NLA_BINARY_EXACT
> > > > 
> > > > or so?
> > > 
> > > Maybe rather
> > > 
> > >   #define NLA_ETH_ADDR NLA_BINARY_EXACT, .len = ETH_ALEN
> > >   #define NLA_IP6_ADDR NLA_BINARY_EXACT, .len = sizeof(struct in6_addr)
> > > 
> > > so that one could write
> > > 
> > >   { .type = NLA_ETH_ADDR }
> > 
> > Yeah, that's possible. I considered it for a second, but it was slightly
> > too magical for my taste :-)
> > 
> > Better pick a different "namespace", perhaps NLA_POLICY_ETH_ADDR or so?
> 
> What about
> #define NLA_FIELD_ETH_ADDR  { .type = NLA_BINARY_EXACT, .len = ETH_ALEN }
> 
> Or even
> #define NLA_FIELD_BINARY_EXACT(_len)	{ .type = NLA_BINARY_EXACT, .len = (_len) }
> #define NLA_FIELD_ETH_ADDR		NLA_FIELD_BINARY_EXACT(ETH_ALEN)
> 
> So that one would just:
>    [MYADDR] = NLA_FIELD_ETH_ADDR,

Yes, that's how I understoold Johannes' proposal above.

Michal Kubecek