Re: config questions

[David Brownell <david-b@pacbell.net>]

> I just finished (successfully after much pain) get hotplug to initialize a 
> device for me when it was plugged in.  But to do this I had to bypass all of 
> the existing net.agent script.

Hmm, you didn't say what Linux distro you're using.  They differ
in how they manage network interfaces ... though there does seem
to be a common failing of requring interfaces to be predefined,
combined with inadequate (or even incorrect) documentation on
how to predefine them.

But then it's complicated by the fact that different network devices
all have different initialization models.  At least some of those
issues are already noted in the net.agent script.


> I am guessing I didn't find the right documentation.  I will tell you what I 
> did and hopefully someone can tell me what I should have done.
> 
> Have usbnet loaded as a module.

Not necessary, it'll be modprobed when needed.  Did you look at

         http://www.linux-usb.org/usbnet/

for information about this driver?  Your question made me push out
some pending updates, which should get synced to the mirrors sometime
tonight (document date 28 August).  More examples, including zcip,
but not yet a complete "out of the box" config example (except for a
simple laptop/desktop setup).

The configuration I'd like to see work is basically combining the
bridge tools (brctl etc) and zeroconf (zcip, plus ...) so those
interfaces never require preconfiguration.  (It'd be an option,
but not the only or preferred one.)


> in /etc/hotplug/net.agent  before anything, do 
> 
> 
> mesg Checking for subscript for $INTERFACE $ACTION
> if [ -x "/etc/hotplug/interfaces/$INTERFACE" ] ; then
>     mesg Calling subscript for $INTERFACE $ACTION
>     /etc/hotplug/interfaces/$INTERFACE $ACTION
>     exit 0
> fi
> 
> and in /etc/hotplug/interfaces reacted to the arguments registered and 
> derigistered to do what I needed for /dev/usb0

There's no such thing as /dev/usb0!  :)

But what you're doing there is defining a new network administration
policy, which is something hotplug has so far avoided doing.  Though
I'm pretty much convinced it'll be essential for IP-over-USB, since
otherwise distros will continue requiring pre-configuration (yeech)
instead of just making that a (less desirable) policy option.

The /etc/sysconfig/network-scripts/ifcfg-usb0 script is how at least
some distros handle that problem, not that there's good documentation
on how to make them work.  Not interfaces/usb0.


> Ideally I would always like to say... for devX put file into interfaces/devX 
> and in that file do X for plugged in and Y for unplugged.  Just like the 
> init.d scripts.

Whereas, the networking scripts currently invoke "ifup" on interfaces
that are known to the distro's network admin tools.  They can't often
do anything useful on "unregister", like "ifdown", since the interface
is gone by then.  (Though ISTR that either SuSE or Debian had a version
of "ifup" that updated some user mode database, so "ifdown" had to purge
that data...)  And sysadmin tools don't often handle "usb0" (etc) yet.


> Information on why my approach is wrong would help, the page 
> http://linux-hotplug.sourceforge.net/
> talked a lot about what hotplug without ever getting to the one question most 
> people would have...
> "I have new device X and I want Y to happen when I plug it in.  What do I do?"

If you're asking as a user, the answer is:  "It's probably supposed to happen
automatically, without needing pre-configuration.  But not all the tools are
there yet."

If you're asking as a developer, then "UTSL, and good patches always help" is
closer to the answer.  Most of those pages are directed towards developers
right now.

And it'd be a big help if someone packaged a general "hotplug event triggers
user dialog" facility, so that when sysadmin attention is needed, the system
can at least initiate a conversation with the user.

- Dave



> Thanks for any information.  If it turns out this description isn't in 
> existence yet (for users who just want an answer to the above question, not 
> understand how hotplug works) then I might do one up.
> 
> Ian.
> 
> 




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