> Occasionally, drivers care about the value that idr associates with
 > their pointers.
 > 
 > Today we have idr_get_new_above() which allocates a new idr entry
 > above or equal to a given starting id, but sometimes drivers need to
 > force an exact value.
 > 
 > To overcome this small API gap, drivers are wrapping idr_get_new_above
 > and then either BUG_ON() or just call idr_remove() and returns -EBUSY
 > when idr allocates them an id which is different than their requested
 > value.

Looks fine to me as an improvement over the status quo, but I wonder how
many of these places could use the radix_tree stuff instead?  If you're
not using the ability of the idr code to assign an id for you, then it
seems the radix_tree API is a better fit.

 - R.