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

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Date:   Wed, 5 Jun 2019 10:47:58 +0900
From:   Lorenzo Colitti <lorenzo@...gle.com>
To:     Hangbin Liu <liuhangbin@...il.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>,
        Mateusz Bajorski <mateusz.bajorski@...ia.com>,
        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 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.