[nzlug] Completely unmounting USB device

[Robin Sheat]

I have an MP3 player that charges on USB. When you first connect it, the 
computer recognises it and talks to it, and all is well. However, I want to 
know how much it is charged. According to the manual, you can do this in 
windows by using the 'safely remove hardware' thing. In Linux, unmounting it 
removes the mountpoint, but it doesn't seem to remove the device node.

How can I tell Linux to completely stop talking to a USB device so it'll show 
me the amount that it's charged?

I note that my camera seems to be able to do this[0], when I unmount it, the 
colour of the light changes, but it seems to be using a different method of 
detecting than this MP3 player.

Robin.

[0] at least, up until I lost the USB cable in Australia. Fortunately, feisty 
now works with the SD card reader on my laptop.