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

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Message-ID: <eef3b598-2590-5c62-e79d-76eb46fae5ff@cumulusnetworks.com>
Date:   Tue, 4 Jun 2019 21:57:56 -0600
From:   David Ahern <dsa@...ulusnetworks.com>
To:     Hangbin Liu <liuhangbin@...il.com>, David Ahern <dsahern@...il.com>
Cc:     David Miller <davem@...emloft.net>, Yaro Slav <yaro330@...il.com>,
        Thomas Haller <thaller@...hat.com>,
        Lorenzo Colitti <lorenzo@...gle.com>, astrachan@...gle.com,
        Greg KH <greg@...ah.com>,
        Linux NetDev <netdev@...r.kernel.org>,
        mateusz.bajorski@...ia.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 6/4/19 7:43 PM, Hangbin Liu wrote:
> Hi David Ahern,
> 
> On Fri, May 31, 2019 at 06:43:42PM -0700, Maciej Żenczykowski wrote:
>> FYI, this userspace visible change in behaviour breaks Android.
>>
>> We rely on being able to add a rule and either have a dup be created
>> (in which case we'll remove it later) or have it fail with EEXIST (in
>> which case we won't remove it later).
>>
>> Returning 0 makes atomically changing a rule difficult.
>>
>> Please revert.
> What do you think? Should I rever this commit?

I think it is crazy to add multiple identical rules given the linear
effect on performance. But, since it breaks Android, it has to be reverted.