RFC: new modes in network-manager 0.7 + ifupdown

[James Westby]

On Tue, 2008-10-07 at 11:33 +0200, Alexander Sack wrote:
> To address this I currently see two approaches for "Managed mode".
> 
>  1. disable ifup/ifdown for NM managed devices completely: this
>  probably would be the clean solution and would reflect the fact that
>  NM managed network devices cannot/must not be managed through
>  ifup/ifdown.
> 
>  2. the other option is to only prevent ifup/ifdown from automatically
>  interfering with NetworkManager and leave the decision whether a user
>  wants to manually mess with his NetworkManager managed devices through
>  ifup/ifdown to the user: To achieve this we could a) disable the "-a"
>  option in ifup or b) add special code to the networking init.d script.
> 
> For now, my personal preference is solution 2a). It does not disable
> ifup/ifdown completely, while it would prevent issues due to devices
> being accidentially/automatically managed my ifup/ifdown at startup.

Hi Alexander,

After working with a user to debug and fix 

  https://bugs.launchpad.net/bugs/281984

which was a small logic bug in the change to ifupdown to look for
managed mode we had a short discussion about the fragility of this
change.

Once managed mode is default, or a user explicitly sets it, if
they then remove network-manager then ifupdown will still refuse
to act on the interfaces, even though they won't have nm managing
them. While it's not really a supported case it could be worth
fixing it now before anyone hits it.

The proposal was to extend the check for managed=true to also
look for something outside of /etc/ installed by network-manager,
so that if you have just the configuration file ifupdown will still
work.

This obviously introduces another failure condition, that if
network-manager renames or removes the chosen file ifupdown
will start acting on the interfaces again. We could obviously
design something that was reasonably robust though.

What do you think?

Thanks,

James