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 09:43:45 +0800
From:   Hangbin Liu <liuhangbin@...il.com>
To:     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, 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

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?

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.

Thanks
Hangbin

> 
> On Wed, May 8, 2019 at 9:39 AM David Miller <davem@...emloft.net> wrote:
> >
> > From: Hangbin Liu <liuhangbin@...il.com>
> > Date: Tue,  7 May 2019 17:11:18 +0800
> >
> > > With commit 153380ec4b9 ("fib_rules: Added NLM_F_EXCL support to
> > > fib_nl_newrule") we now able to check if a rule already exists. But this
> > > only works with iproute2. For other tools like libnl, NetworkManager,
> > > it still could add duplicate rules with only NLM_F_CREATE flag, like
> > >
> > > [localhost ~ ]# ip rule
> > > 0:      from all lookup local
> > > 32766:  from all lookup main
> > > 32767:  from all lookup default
> > > 100000: from 192.168.7.5 lookup 5
> > > 100000: from 192.168.7.5 lookup 5
> > >
> > > As it doesn't make sense to create two duplicate rules, let's just return
> > > 0 if the rule exists.
> > >
> > > Fixes: 153380ec4b9 ("fib_rules: Added NLM_F_EXCL support to fib_nl_newrule")
> > > Reported-by: Thomas Haller <thaller@...hat.com>
> > > Signed-off-by: Hangbin Liu <liuhangbin@...il.com>
> >
> > Applied and queued up for -stable, thanks.