How to detect whether media is present in a reader?

[Michael Hamilton <michael@actrix.gen.nz>]

I've attempted to develop a desktop integration script for usb 
storage devices. ( http://freshmeat.net/projects/usbmount/ )

Before anyone reading this thinks this a trivial problem,
you should read the requirements/issues detailed at the bottom
of http://users.actrix.co.nz/michael/usbmount.html - many aspects
of the USB/SCSI system make this task much harder than it should
be. I would recommend anyone working on this area to take a look
at my script and see the fun currently involved - and then see
if what they're working on will make life easier.

In the mean time, working with what is available on current 
distributions, I'm looking for a solution to one piece of the
puzzle...

I would like to be able to detect whether media is present
in a reader or not (eg Compact Flash Card reader).  A small 
piece of C for efficiently obtaining the media state would be 
good.  I would like a solution for both 2.4 and 2.6, but 
I'll settle for what I can get.  Does anyone have some sample
code?

From looking at what's available I get the impression that
some variant on polling is the only solution for such problems.  
Is this really the case - even for USB?

I've looked at supermount and submount - I'm not sure they
offer a better solution than my own attempts thus far - 
I don't think they can tackle all of the requirements listed
on my webpage. 

I was also playing with sginfo from sg3_utils ( 
http://www.torque.net/sg/u_index.html ).  But this can be
slow, and, in the absence of media, some of the sg3_utils
probes can get stuck in system calls (which requires a
reboot).

If I had a simple/efficient way to poll a device's media 
insertion state, I think my script could then fully automate 
almost all aspects of desktop integration of usb storage.

Thanks.





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