just to add some clarification.. our ideal system would look something like this:
/net/mainsys_cpu1
/net/mainsys_cpu2
/net/dock1
/net/dock2
where dock1 and dock2 are hot swappable external modules. The modules do know in what slot they are, so they can be 
assigned unique hostnames upon boot.

If you have other means to know a node goes away, and a node comes in,
you can do this more reliable.

1) When a node goes away, you can tell QNET by doing a:

	rmdir("/net/dock1");

   This will force QNET to do a "node down" on /net/dock1, and clean up
accordingly. 

2) When a node coming in, you can force QNET to "discover" it, by:

      while((fd = open("/net/dock1/dev/null", O_RDONLY)) == -1) {
		sleep(1);
	}

Regards,

-xtang

> -----Original Message-----
> From: Marc Roessler [mailto:community-noreply@qnx.com]
> Sent: January 22, 2009 7:47 AM
> To: technology-networking
> Subject: QNet with "hot swappable" devices, boot times
> 
> Hi,
> 
> we are designing a system where we have several integrated CPUs and
also
> external modules that are connected and disconnected while the main
system
> is running.
> 
> I am concerned about the following:
> 
> 1. how fast will the QNX nodes find each other upon system boot? Is
there
> anything we can do to aid node discovery to be faster/more efficient?
> Anything one should avoid?
> 
> 2. when the external modules are un-docked, the old node will be
lingering
> for some time in /net. We do have knowledge whether the external
module is
> connected or not (be means of physical contacts), can we use this to
> somehow make qnx "purge" the old /net entry right away? Our worst case
> scenario would be undocking an external module, plugging in another
(but
> physically identical) module, and the old connection would linger and
the
> new one couldn't be used...
> 
> 3. currently, we have only one external module docked/plugged in. My
plan
> was to give each module a unique hostname, so those appear nicely with
an
> intelligible name under /net. Now the potential problem is:
> a) what happens when in later versions there are two identical
external
> modules plugged in
> b) what happens to the names upon undocking a module and swapping it
for
> another one? Will anybody notice? Can anybody notice? How to tell the
main
> system software that now another module has been docked in?
> 
> Thanks & Greetings,
>  Marc
> 
> _______________________________________________
> Technology
> http://community.qnx.com/sf/go/post20568