From mboxrd@z Thu Jan  1 00:00:00 1970
From: Al Viro <viro@ZenIV.linux.org.uk>
Subject: Re: [PATCH 2/7] mark root hnode explicitly
Date: Fri, 7 Sep 2018 04:04:38 +0100
Message-ID: <20180907030438.GX19965@ZenIV.linux.org.uk>
References: <20180905190134.GQ19965@ZenIV.linux.org.uk>
 <20180905190414.5477-1-viro@ZenIV.linux.org.uk>
 <20180905190414.5477-2-viro@ZenIV.linux.org.uk>
 <8d3e140a-eb1b-3aae-d9e7-36d103a54e5e@mojatatu.com>
 <5689c19a-c4fb-24c1-4594-86f2639faa98@mojatatu.com>
 <20180906105933.GU19965@ZenIV.linux.org.uk>
 <CAM_iQpUDpKB2y0Yy5YJjj7MALGsDLJKpdXYZkydmCo1N_uo=FA@mail.gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: Jamal Hadi Salim <jhs@mojatatu.com>,
        Linux Kernel Network Developers <netdev@vger.kernel.org>,
        Jiri Pirko <jiri@resnulli.us>
To: Cong Wang <xiyou.wangcong@gmail.com>
Return-path: <netdev-owner@vger.kernel.org>
Received: from zeniv.linux.org.uk ([195.92.253.2]:44856 "EHLO
        ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1725785AbeIGHnT (ORCPT
        <rfc822;netdev@vger.kernel.org>); Fri, 7 Sep 2018 03:43:19 -0400
Content-Disposition: inline
In-Reply-To: <CAM_iQpUDpKB2y0Yy5YJjj7MALGsDLJKpdXYZkydmCo1N_uo=FA@mail.gmail.com>
Sender: netdev-owner@vger.kernel.org
List-ID: <netdev.vger.kernel.org>

On Thu, Sep 06, 2018 at 07:57:25PM -0700, Cong Wang wrote:

> > -       if (root_ht == ht) {
> > +       if (ht->is_root) {
> 
> 
> What's wrong with comparing pointers with root ht?

The fact that there may be more than one tcf_proto sharing tp->data.

> >                 NL_SET_ERR_MSG_MOD(extack, "Not allowed to delete root node");
> >                 return -EINVAL;
> >         }
> > @@ -795,6 +797,10 @@ static int u32_set_parms(struct net *net, struct tcf_proto *tp,
> >                                 NL_SET_ERR_MSG_MOD(extack, "Link hash table not found");
> >                                 return -EINVAL;
> >                         }
> > +                       if (ht_down->is_root) {
> 
> root ht is saved in tp->root, so you can compare ht_down with it too,
> if you want.
> 
> If this check is all what you need, you don't need an extra flag.

Again, *which* tp?  We can trivially check that we are not linking to/deleting
our own root, sure.  But there's nothing to stop doing the same via another
tcf_proto...