Re: question about default values for per-namespace settings

[Serge Hallyn <serge.hallyn-GeWIH/nMZzLQT0dZR+AlfA@public.gmane.org>]

Quoting Vasily Averin (vvs-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org):
> Dear Tejun,
> 
> how do you think, which defaults should be used for per-namespace settings in general case
> and for per-netns sysctls especially? Do we have some common position about this or
> perhaps we already have some setting that allows to select desired behavior?
> 
> I'm preparing patch that makes per-netns sysctls in br_netfilter,
> to be able to enable/disable br-nf-call processing in each network namespace independently.
> 
> I've initialized sysctl values in each netns by system defaults, like it was done in similar cases.
> However Bart pointed that "this does introduce a bit of backwards incompatibility":
> currently all netns shares the br_netfilter sysctl settings applied in init_net.
> 
> From OpenVz point of view containers should be properly isolated,
> should have predictable initial configuration
> and should not depend on settings applied in another containers.

In 'another container' no, but if you are starting a nested container, then
the from the parent container, yes.  Not from init_net.

> On the other hand independent containers is only one of possible usecases,
> and I have no strong objections against Bart's proposal. Frankly speaking
> initially I've planned to copy setting from init_net too.
> 
> To make possible both variants I can introduce one more setting,
> it allows to specify desired behavior:
> to use system defaults or to copy current settings from init_net.
> 
> However probably the same dilemma was observed in another subsystems?
> Perhaps this selector already exists?
> 
> If isn't, how do you think, should I introduce some new global parameter,
> or may be it should be some local bridge-only-related setting?
> 
> Thank you,
> 	Vasily Averin
> 
> you can find some more details about my patch in netfilter-devel@
> [PATCH RFC v3 2/2] br_netfilter: per-netns copy of structure for sysctl flags
> On 05/13/2014 11:28 PM, Bart De Schuymer wrote:
> > Vasily Averin schreef op 12/05/2014 22:11:
> >> On 05/12/2014 11:04 PM, Bart De Schuymer wrote:
> >>> Vasily Averin schreef op 12/05/2014 18:32:
> >>>> pernet_operations creates per-netns copy of common structure for sysctl flags
> >>>> and initialize it values taken from init_brnf_net.
> >>>>
> >>>> Signed-off-by: Vasily Averin <vvs-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>
> >>>
> >>>> +static int __net_init brnf_net_init(struct net *net)
> >>>> +{
> >>>> +    struct brnf_net *bn = brnf_net(net);
> >>>> +
> >>>> +    memcpy(bn, &init_brnf_net, sizeof(struct brnf_net));
> >>>> +    bn->net = net;
> >>>> +    return brnf_sysctl_net_register(bn);
> >>>
> >>> This does introduce a bit of backwards incompatibility (easily fixed
> >>> by adapting scripts), but this is really unavoidable when
> >>> transforming an existing global configuration to a per-netns
> >>> configuration. I'm ok with it.
> >>
> >> Could you please explain, which backward incompatibility you mean here?
> >> Nobody changes values init_brnf_net,
> >> init_net have own copy, like any other network namespaces.
> > 
> > Well, init_brnf_net is never written to, so it keeps the default flags.
> > If a new netns is created, a copy of the contents of init_brnf_net is made. So, whenever a netns is created, it starts with the default flags (e.g. brnf_call_iptables is always 1 for a newly created netns).
> > 
> > In the current kernel, when a new netns is created, the configuration of the main netns is used (the proc system doesn't even show the flags in the created netns): if brnf_call_iptables is 0 before the new netns is created, iptables won't see bridged IP traffic in the new netns.
> > With your patch, this behaviour will change.
> > 
> > It's possible to alter your patch to keep the same behaviour as before at netns creation, but always starting from the same defaults is cleaner.
> 
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