[Bug 135909] Re: wpa_supplicant isn't killed on unplug

[Alan Jenkins]

Hmm.  I'm not using the same setup now, but I'm still able to test it.

"allow-hotplug" seems to have stopped working completely in Ubuntu
12.04, despite being still mentioned in the man page.  I.e. the
interface is not brought up automatically when I plug the hardware in.
Maybe it didn't get tested because everyone uses NetworkManager.  (I
certainly do nowadays :).

I compared debian with ubuntu 12.04.  Hotplug works on debian 6.0.  It
seems to work through /lib/udev/net.agent, although I can't see where
its called from.  Current debian unstable also has net.agent.  In both
cases it's provided by the udev package.

On Ubuntu 12.04, there's no net.agent.  "grep -r ifup /lib/udev/" finds
"bridge-network-interface", but nothing else.  "apt-file seach
net.agent" shows that no package contains this file.

If someone else needs to report this as a separate bug, feel free.  You
can simulate unplug / hotplug easily enough.  Use "modprobe -r <your-
network-driver>; modprobe <you-network-driver>".  (To find the driver,
check "ls -l /sys/class/net/*/device/driver/module").  Just remember you
need set the interface up using /etc/network/interfaces.

The absence of net.agent in ubuntu, compared to debian unstable, looks
like a smoking gun to me.  Ubuntu has changed something from upstream,
so the question is why.  If something else is supposed to do the same
job, then where is that something?

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https://bugs.launchpad.net/bugs/135909

Title:
  wpa_supplicant isn't killed on unplug

Status in “ifupdown” package in Ubuntu:
  Incomplete

Bug description:
  Binary package hint: wpasupplicant

  I have a USB wireless wireless adaptor.  I have a use case which is
  not well suited to NetworkManager - single AP and with a multi-user
  system.  So I set it up using "wpa-" options in
  /etc/network/interfaces instead, and added a "mapping hotplug" section
  in case a user should unplug the adaptor and replug it for some reason
  :-).

  So AFAIK what should happen is a copy of wpa_supplicant is started
  when the device is detected, and killed when it is removed.  The first
  bit works, and I have wonderful hotplug goodness.

  Unfortunately the killing on removal doesn't seem to work properly.
  For me it's mainly a matter of tidyness and correctness.  However the
  surplus process is consuming resources: in particular it shows up on
  powertop as being responsible for 3 wakeups per second - and the
  target for efficient idling is somewhere under 10 per second.

  I know which scripts (ifupdown hooks) are supposed to be taking care
  of this , but I haven't debugged it.  Any hints on debugging this sort
  of thing would be appreciated.

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