netdev - Re: [patch net-next v4 03/12] net: sched: introduce chain object to uapi

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Date:   Wed, 25 Jul 2018 08:46:45 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Simon Horman <simon.horman@...ronome.com>,
        john.hurley@...ronome.com, David Ahern <dsahern@...il.com>,
        mlxsw@...lanox.com, sridhar.samudrala@...el.com
Subject: Re: [patch net-next v4 03/12] net: sched: introduce chain object to
 uapi

Wed, Jul 25, 2018 at 01:20:08AM CEST, xiyou.wangcong@...il.com wrote:
>On Tue, Jul 24, 2018 at 3:30 PM Cong Wang <xiyou.wangcong@...il.com> wrote:
>>
>> On Mon, Jul 23, 2018 at 12:25 AM Jiri Pirko <jiri@...nulli.us> wrote:
>> > +       switch (n->nlmsg_type) {
>> > +       case RTM_NEWCHAIN:
>> > +               /* In case the chain was successfully added, take a reference
>> > +                * to the chain. This ensures that an empty chain
>> > +                * does not disappear at the end of this function.
>> > +                */
>> > +               tcf_chain_hold(chain);
>> > +               chain->explicitly_created = true;
>> > +               tc_chain_notify(chain, NULL, 0, NLM_F_CREATE | NLM_F_EXCL,
>> > +                               RTM_NEWCHAIN, false);
>> > +               break;
>> > +       case RTM_DELCHAIN:
>> > +               /* Flush the chain first as the user requested chain removal. */
>> > +               tcf_chain_flush(chain);
>> > +               /* In case the chain was successfully deleted, put a reference
>> > +                * to the chain previously taken during addition.
>> > +                */
>> > +               tcf_chain_put_explicitly_created(chain);
>> > +               break;
>>
>> I don't see you send notification to user-space when deleting a chain,
>> am I missing anything?
>
>Oh, it is hidden in tcf_chain_put():
>
>void tcf_chain_put(struct tcf_chain *chain)
>{
>        if (--chain->refcnt == 0) {
>                tc_chain_notify(chain, NULL, 0, 0, RTM_DELCHAIN, false);
>                tc_chain_tmplt_del(chain);
>                tcf_chain_destroy(chain);
>        }
>}
>
>So, you only send out notification when the last refcnt is gone.
>
>If the chain that is being deleted by a user is still used by an action,
>you return 0 or -EPERM?

0 and the chain stays there until the action is removed. Hmm, do you thing
that -EPERM should be returned in that case? The thing is, we have to
flush the chain in order to see the action references are there. We would
have to have 2 ref counters, one for filter, one for actions.
What do you think?