netdev - Re: [PATCH net-next 1/2 v2] net sched actions: dump more than TCA_ACT_MAX

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Message-ID: <1492566545.10587.159.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Tue, 18 Apr 2017 18:49:05 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org, jiri@...nulli.us,
        xiyou.wangcong@...il.com
Subject: Re: [PATCH net-next 1/2 v2] net sched actions: dump more than
 TCA_ACT_MAX_PRIO actions per batch

On Tue, 2017-04-18 at 21:14 -0400, Jamal Hadi Salim wrote:
> From: Jamal Hadi Salim <jhs@...atatu.com>

So there is no more limit ? How user is supposed to size the buffer for
recvmsg() ?

>  	t->tca__pad1 = 0;
> @@ -1113,6 +1133,9 @@ static int tc_dump_action(struct sk_buff *skb, struct netlink_callback *cb)
>  	if (ret > 0) {
>  		nla_nest_end(skb, nest);
>  		ret = skb->len;
> +		if (nla_put_u32(skb, TCAA_ACT_COUNT, cb->args[1]))
> +			goto out_module_put;
> +		cb->args[1] = 0;

I really do not see how you manage to get room to add one additional
attribute, if dump had to stop at N actions, filling whole skb.

You might be lucky because nla_put_u32() wants a bit less space than an
action ?

Presumably you need to reserve space before the dump of actions.