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Date: Thu, 21 Oct 2021 09:08:34 +0800
From: Hangbin Liu <liuhangbin@gmail.com>
Message-ID: <YXC9kgPGv+Xb85Sc@Laptop-X1>
References: <20211018082612.625417-1-liuhangbin@gmail.com>
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 <YW9qiUhDKT+56wkd@Laptop-X1> <20211020081937.70059049@hermes.local>
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Subject: Re: [Bridge] [PATCH net] net: bridge: mcast: Do not allow users to
 set IGMP counter/timer to zero
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To: Stephen Hemminger <stephen@networkplumber.org>
Cc: Nikolay Aleksandrov <razor@blackwall.org>, bridge@lists.linux-foundation.org, Nikolay Aleksandrov <nikolay@nvidia.com>, roopa@nvidia.com, kuba@kernel.org, davem@davemloft.net

On Wed, Oct 20, 2021 at 08:19:37AM -0700, Stephen Hemminger wrote:
> > On Tue, Oct 19, 2021 at 07:09:42PM +0300, Nikolay Aleksandrov wrote:
> > > > I started this patch when I saw there is not limit for setting
> > > > multicast_membership_interval to 0, which will cause bridge remove the
> > > > mdb directly after adding. Do you think this is a problem.
> > > > 
> > > > And what about others? I don't think there is a meaning to set other intervals
> > > > to 0.
> > > >   
> > > 
> > > The problem is not if there is meaning, we cannot start restricting option values now after
> > > they've become uapi (and have been for a very long time) because we can break user-space even
> > > though chances are pretty low. I don't think this patch is acceptable, I commented on the other
> > > patch issues but they don't matter because of this.  
> > 
> > OK, I got your mean, we should not restrict the configurations based on whether
> > there is a meaning.
> > 
> > Thanks
> > Hangbin
> 
> Maybe the bridge command could enforce that the value set are sane relative
> to the RFC?  We already fixup some things in iproute2 utilities to workaround
> places where changing defaults in kernel would break userspace.

I'm afraid this may make user more confused. As user could also echo the
values via sys fs directly. e.g.

# ip link set br0 type bridge mcast_query_interval 0
Error: Invalid QI, must greater than 0.
# echo 0 > /sys/devices/virtual/net/br0/bridge/multicast_query_interval

Then ip -d link show br0 would show the mcast_query_interval is 0.

Thanks
Hangbin