netdev - Re: [PATCH net-next 1/6] ethtool: wire up get policies to ops

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Date:   Mon, 5 Oct 2020 12:41:47 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     davem@...emloft.net, netdev@...r.kernel.org, kernel-team@...com,
        jiri@...nulli.us, andrew@...n.ch, mkubecek@...e.cz
Subject: Re: [PATCH net-next 1/6] ethtool: wire up get policies to ops

On Mon, 05 Oct 2020 21:33:55 +0200 Johannes Berg wrote:
> > What I'm saying is that my preference would be:
> > 
> > const struct nla_policy policy[OTHER_ATTR + 1] = {
> > 	[HEADER]	= NLA_POLICY(...)
> > 	[OTHER_ATTR]	= NLA_POLICY(...)
> > };
> > 
> > extern const struct nla_policy policy[OTHER_ATTR + 1];
> > 
> > op = {
> > 	.policy = policy,
> > 	.max_attr = ARRAY_SIZE(policy) - 1,
> > }
> > 
> > Since it's harder to forget to update the op (you don't have to update
> > op, and compiler will complain about the extern out of sync).  
> 
> Yeah.
> 
> I was thinking the third way ;-)
> 
> const struct nla_policy policy[] = {
> 	[HEADER]	= NLA_POLICY(...)
> 	[OTHER_ATTR]	= NLA_POLICY(...)
> };
> 
> op = {
> 	.policy = policy,
> 	.maxattr = ARRAY_SIZE(policy) - 1,
> };
> 
> 
> Now you can freely add any attributes, and, due to strict validation,
> anything not specified in the policy will be rejected, whether by being
> out of range (> maxattr) or not specified (NLA_UNSPEC).

100%, but in ethtool policy is defined in a different compilation unit
than the op array.