Re: [Bridge] [PATCH net] net: bridge: mcast: Do not allow users to set IGMP counter/timer to zero

[Hangbin Liu <liuhangbin@gmail.com>]

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