Environment woes

[Josua Dietze <digidietze@draisberghof.de>]

Hi everyone,

I am in need of a friendly hint regarding a delicate matter ...

I maintain a Linux tool to put USB devices from one mode (or state) to 
the other. Many wireless sticks support that "feature", showing up as 
a storage device and providing their Windows drivers onboard. To be 
used as modems they are switched by these drivers (once they are 
installed) to their second mode.

This can be handled in Linux and is properly tested.

Usually there is more than one interface exposed after the mode 
switch, but only one is suitable for a wireless connection; binding 
the GSM driver ("option") or the generic serial driver will add 
multiple ports though (ttyUSB).

Up to now I have used a rule to add a symlink to the "right" port; the 
check is done by a script via "PROGRAM". If the port is not right, the 
result of the script is empty, thus no symlink:

ACTION="add", KERNEL="ttyUSB*", PROGRAM="<script> %p", SYMLINK="%c"

To handle *only* the device that was switched by my other rules, I 
stored the bus and device number during the switching process in a 
temporary file which is then used by the <script>. I had tried to work 
with ENV first but failed.

You might already guess what I'm going to ask ...

I was reprimanded - and rightly so - for using the temp file, which is 
said to be insecure and not working at boot time.
But I am at a loss how I should signal from one enumeration event to 
annother without using a file; neither ENV nor IMPORT are working, 
probably because the different modes behave like two unrelated 
devices, storage and serial. Quite often the USB ID changes with the 
mode switch.

Is there really no environment that can be accessed from both 
scripts/events?
Or is there a third way maybe?
The order of events is guaranteed in my case ...


Thanks,
Josua Dietze