Bug#809166: networking.service does not prevent ifdown with network file systems

[Guus Sliepen]

On Wed, Jan 13, 2016 at 04:00:16PM +0100, Martin Pitt wrote:

> > Why should ifupdown tear down the network on shutdown then?
> 
> E. g. LTSP creates an ifupdown stanza like "iface eth0 inet manual"
> for the remote root interface to prevent NetworkManager from
> (auto-)connecting/disconnecting eth0. NM ignores interfaces that are
> configured in ifupdown, thus preventing the user from  shooting
> herself into the foot by accidentally/maliciously clicking on
> "disconnect" in the network icon.

Ugh. That's totally wrong. Why doesn't LTSP tell NetworkManager itself
to stop messing with eth0? Instead of adding a stanza to /e/n/i, just
write this to /etc/NetworkManager/NetworkManager.conf:

[keyfile]
unmanaged-devices=interface-name=eth0

> This use case actually got broken
> by the overzealous patch in #809169 which added this:
> 
>    down
> +    /bin/ip link set dev %iface% down 2>/dev/null || true \
> +        if (iface_is_link())
> 
> for "manual" interfaces. I. e. "ifdown eth0" on the above "manual"
> interface example would actually down the interface. This isn't
> documented behaviour, and breaks this (IMHO) valid use case to mark an
> interface as "please leave me alone".

I'd say that the latter use case is invalid.

> I also looked at open-iscsi in Ubuntu. That package has a weird patch
> which hacks ifupdown's state files to think that eth0 is already up,

Oh god. That's also completely wrong. Ifupdown 0.8 and later uses
per-interface state files (because they can be locked individually), the
/run/network/ifstate file is still there for now but it might be phased
out.

> Again the check_network_file_systems() check prevented a shutdown hang
> here. But this whole approach is just wrong, and we need to fix that
> on the Ubuntu side to generate an ifupdown interface stanza on first
> boot on the fly (this is also necessary for the ifnames changes, as
> it's not guaranteed to be eth0 these days). This part isn't really
> relevant for you, but I wanted to mention it here for the record.

What I am willing to do is to add the keyword "no-auto-down" to
interface stanza's, which will prevent the interface from being brought
down using "ifdown -a".

-- 
Met vriendelijke groet / with kind regards,
      Guus Sliepen <guus at debian.org>
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