dhcpcd-discuss

On 04/09/2020 20:59, Jouke Witteveen wrote:
> I do think something could really be improved, but it may be too
> difficult to fix it on a very short notice. Here is a complete
> session, annotated with "----", that shows the issue:
>
> # cat /tmp/ifplugd.action
> #!/bin/bash
>
> case "$2" in
>    up)
>      dhcpcd "$1";;
>    down)
>      dhcpcd -x "$1";;
> esac
> # /usr/bin/ifplugd -i eth0 -r /tmp/ifplugd.action -ns
> ifplugd 0.28 initializing.
> Using interface eth0/[...] with driver <e1000e> (version: 3.2.6-k)
> Using detection mode: SIOCETHTOOL
> Initialization complete, link beat detected.
> Executing '/tmp/ifplugd.action eth0 up'.
> client: dhcpcd-9.1.4 starting
> client: DUID [...]
> client: eth0: IAID [...]
> client: eth0: soliciting an IPv6 router
> client: eth0: Router Advertisement from [...]
> client: eth0: rebinding lease of 192.168.[...]
> client: eth0: leased 192.168.[...] for 86400 seconds
> client: eth0: adding route to 192.168.[...]/24
> client: eth0: adding default route via 192.168.[...]
> client: forked to background, child pid [...]
> ^Z  ---- At this point the connection is fine and dhcpcd fully operational
> [1]+  Stopped                 /usr/bin/ifplugd -i eth0 -r
> /tmp/ifplugd.action -ns
> # bg
> [1]+ /usr/bin/ifplugd -i eth0 -r /tmp/ifplugd.action -ns &
> # ifplugd -i eth0 -z
> Killing child.  ---- This would show "running" with dhcpcd 8
> # dhcpcd -x eth0  ---- [1]
> sending signal TERM to pid [...]
> waiting for pid [...] to exit
> # Program executed successfully.  ---- output from the backgrounded ifplugd
> # ifplugd -i eth0 -z  ---- [1]
> SIGHUP: Running, link detected on eth0: yes

I can replicate this on Devuan, thanks for the example.
My diagnosis is that ifplugd is crashing - the equivalent setup using netplug 
rather than ifplugd works fine.

The fix is to setup a sockpair, close stdout/stderr when doing the initial fork 
and then send stderr via the socketpair which the launcher process can then send 
to the real stderr.

What ifplugd is doing with stderr to cause this, I really don't know.

This is probably a cleaner way of doing things, but we have now lost all output 
from dhcpcd-run-hooks from the initial start which I sometimes use to debug 
with. I will work on that later, but now the master branch should be good for you.

Can you test it please?

Roy