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

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Date:   Mon, 05 Oct 2020 21:33:55 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     Jakub Kicinski <kuba@...nel.org>
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, 2020-10-05 at 12:31 -0700, Jakub Kicinski wrote:

> Yea, I think we're both confused. Agreed with the above.
> 
> Are you suggesting:
> 
> const struct nla_policy policy[/* no size */] = {
> 	[HEADER]	= NLA_POLICY(...)
> 	[OTHER_ATTR]	= NLA_POLICY(...)
> };
> 
> extern const struct nla_policy policy[/* no size */];
> 
> op = {
> 	.policy = policy,
> 	.max_attr = OTHER_ATTR,
> }

No, that'd be awkward, for the reason you stated below.

> 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).

johannes