Bug#806949: ifupdown: some tweaks to networking.service

[Bob Proulx]

Martin Pitt wrote:
> Michael Biebl wrote:
> > I still think though, that we should consider allow-hotplug interfaces
> > when dealing with network-online.target.
> > 
> > The reason is, that the debian installer uses allow-hotplug by default.
> 
> Argh, this is indeed a tremendously bad default. So far I had the
> impression that "auto" is for "must be present for booting", and
> "allow-hotplug" is for "bring it up when present, but don't block on
> it on boot". But if the installer always uses allow-hotplug, then I
> think that completely defies trying to make any difference between the
> two.

If a client system requires an NFS mounted file system then the admin
must configure the network to be "auto" and not "allow-hotplug".
The simple reason is that because otherwise it won't work. :-)

When the debian-installer initially installs a system there is no
dependency upon an NFS file system.  It is okay to have allow-hotplug
be the default used by the d-i.  It is a lowest common denominator and
works for most systems.  However if the admin then configures the
system to use a remotely mounted NFS file system part of that
configuration must be to set the interface to "auto" requiring it to
be present.  That's okay.  That is the way it has been for every
release since "allow-hotplug" arrived.

It is also possible to set up other types of mounting such as through
an automounter using autofs, amd, or other systems.  Each of those
will have their own specific needs that must be taken into
consideration.  If someone requires a hotplugged network system and
also wants remote mounting they can set it up but there isn't any
standard configuration for it and they will need to be responsible for
the complexity of it.  Trying to create a magic system that handles
every possible combination will end up failing and just creating a
mess.

Bob
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