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

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Date:   Sat, 1 Jun 2019 02:32:44 -0700
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Maciej Żenczykowski <zenczykowski@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Lorenzo Colitti <lorenzo@...gle.com>, astrachan@...gle.com,
        liuhangbin@...il.com, Linux NetDev <netdev@...r.kernel.org>,
        mateusz.bajorski@...ia.com, dsa@...ulusnetworks.com
Subject: Re: [PATCH net] fib_rules: return 0 directly if an exactly same rule
 exists when NLM_F_EXCL not supplied

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.

That's crazy, but makes sense in an odd way :)

And it explains why my "fix up of the patch" also breaks things, both
patches need to be reverted in the stable trees.  Do you need me to make
a patch to revert this in Linus's tree now, or can you do that?  Just
asking for an existing commit to be reverted is usually a bit harder as
that's not most maintainer's workflow (I know it's not mine.)

thanks,

gre gk-h