Re: [PATCH net-next v2 1/3] net/sched: act_vlan: Fix modify to allow 0

[Davide Caratti <dcaratti@redhat.com>]

On Tue, May 25, 2021 at 06:35:59PM +0300, Boris Sukholitko wrote:
> Currently vlan modification action checks existence of vlan priority by
> comparing it to 0. Therefore it is impossible to modify existing vlan
> tag to have priority 0.
> 
> For example, the following tc command will change the vlan id but will
> not affect vlan priority:
> 
> tc filter add dev eth1 ingress matchall action vlan modify id 300 \
>         priority 0 pipe mirred egress redirect dev eth2

hello Boris, thanks a lot for following up! A small nit below:
 
> diff --git a/net/sched/act_vlan.c b/net/sched/act_vlan.c
> index 1cac3c6fbb49..cca10b5e99c9 100644
> --- a/net/sched/act_vlan.c
> +++ b/net/sched/act_vlan.c

[...]

> @@ -121,6 +121,7 @@ static int tcf_vlan_init(struct net *net, struct nlattr *nla,
>  	struct tc_action_net *tn = net_generic(net, vlan_net_id);
>  	struct nlattr *tb[TCA_VLAN_MAX + 1];
>  	struct tcf_chain *goto_ch = NULL;
> +	bool push_prio_exists = false;
>  	struct tcf_vlan_params *p;
>  	struct tc_vlan *parm;
>  	struct tcf_vlan *v;
> @@ -189,7 +190,8 @@ static int tcf_vlan_init(struct net *net, struct nlattr *nla,
>  			push_proto = htons(ETH_P_8021Q);
>  		}
>  
> -		if (tb[TCA_VLAN_PUSH_VLAN_PRIORITY])
> +		push_prio_exists = !!tb[TCA_VLAN_PUSH_VLAN_PRIORITY];

when the VLAN tag is pushed, not modified, the value of 'push_prio' is
used in the traffic path regardless of the true/false value of
'push_prio_exists'. See below:

 50         case TCA_VLAN_ACT_PUSH:
 51                 err = skb_vlan_push(skb, p->tcfv_push_proto, p->tcfv_push_vid |
 52                                     (p->tcfv_push_prio << VLAN_PRIO_SHIFT));

So, I think that 'p->push_prio_exists' should be identically set to
true when 'v_action' is TCA_VLAN_ACT_PUSH. That would allow a better
display of rules once patch 2 of your series is applied: otherwise,
2 rules configuring the same TCA_VLAN_ACT_PUSH rule would be displayed
differently, depending on whether userspace provided or not the
TCA_VLAN_PUSH_VLAN_PRIORITY attribute set to 0. In other words, the
last hunk should be something like:

@@ -241,6 +243,7 @@ static int tcf_vlan_init(struct net *net, struct nlattr *nla,
 	p->tcfv_action = action;
 	p->tcfv_push_vid = push_vid;
 	p->tcfv_push_prio = push_prio;
+	p->tcfv_push_prio_exists = push_prio_exists || action == TCA_VLAN_ACT_PUSH;


WDYT?

thanks!
-- 
davide