netdev - Re: [PATCH net] fib_rules: return 0 directly if an exactly same rule exists when NLM_F

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Message-ID: <20190605021533.GZ18865@dhcp-12-139.nay.redhat.com>
Date:   Wed, 5 Jun 2019 10:15:33 +0800
From:   Hangbin Liu <liuhangbin@...il.com>
To:     Lorenzo Colitti <lorenzo@...gle.com>
Cc:     David Ahern <dsahern@...il.com>,
        David Miller <davem@...emloft.net>,
        Yaro Slav <yaro330@...il.com>,
        Thomas Haller <thaller@...hat.com>,
        Alistair Strachan <astrachan@...gle.com>,
        Greg KH <greg@...ah.com>,
        Linux NetDev <netdev@...r.kernel.org>,
        David Ahern <dsa@...ulusnetworks.com>,
        Maciej Żenczykowski <zenczykowski@...il.com>
Subject: Re: [PATCH net] fib_rules: return 0 directly if an exactly same rule
 exists when NLM_F_EXCL not supplied

On Wed, Jun 05, 2019 at 10:47:58AM +0900, Lorenzo Colitti wrote:
> On Wed, Jun 5, 2019 at 10:43 AM Hangbin Liu <liuhangbin@...il.com> wrote:
> > Although I'm still not clear what's the difference between
> >
> > a) adding a dup rule and remove it later
> > and
> > b) return 0 directly if the rule exactally the same.
> 
> The Android code updates ip rules by adding the new rule and then
> deleting the old rule. Before this patch, the result of the operation
> is that the old rule is deleted and the new rule exists. After this
> patch, if the new rule is the same as the old rule, then the add does
> nothing and the delete deletes the old rule. The result of the
> operation is that the old rule is deleted and the new rule is no
> longer there, and the rules are broken.

Hi Lorenzo,

How do you add the rules? with ip cmd it should has NLM_F_EXCL flag and
you will get -EEXIST error out.

Thanks
Hangbin