From mboxrd@z Thu Jan  1 00:00:00 1970
From: Cong Wang <xiyou.wangcong@gmail.com>
Subject: Re: [patch net-next v4 03/12] net: sched: introduce chain object to uapi
Date: Tue, 24 Jul 2018 16:20:08 -0700
Message-ID: <CAM_iQpXxOOAw06tGiCmkWrMkU4xoNO8cwTP349vU8AGj--OXVQ@mail.gmail.com>
References: <20180723072312.4153-1-jiri@resnulli.us> <20180723072312.4153-4-jiri@resnulli.us>
 <CAM_iQpU41g_aSd7wbRk5r+hbVRdoDYnLWANjOJtZYgf4qfx0_w@mail.gmail.com>
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Cc: Linux Kernel Network Developers <netdev@vger.kernel.org>,
        David Miller <davem@davemloft.net>,
        Jamal Hadi Salim <jhs@mojatatu.com>,
        Jakub Kicinski <jakub.kicinski@netronome.com>,
        Simon Horman <simon.horman@netronome.com>,
        john.hurley@netronome.com, David Ahern <dsahern@gmail.com>,
        mlxsw@mellanox.com, sridhar.samudrala@intel.com
To: Jiri Pirko <jiri@resnulli.us>
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On Tue, Jul 24, 2018 at 3:30 PM Cong Wang <xiyou.wangcong@gmail.com> wrote:
>
> On Mon, Jul 23, 2018 at 12:25 AM Jiri Pirko <jiri@resnulli.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?