On Mon, 20 Sep 2010 16:11:31 +0200
Ohad Ben-Cohen [off-list ref] wrote:

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.

There are only a handful of users who need this (see below. especially
note the i2c comment :), but it might be nice to have such an API (a
bit less of code, and a bit less error prone).

Would something like the below be desirable/acceptable ?

It seems OK to me - it's an improvement over what we have now.

(untested. and i just picked the simplest and straight-forward way to
implement this; obviously it's not optimal since there's no reason to
even allocate an id if we know it's not the id we're looking for. but
it's enough to get the idea, it's not a hot path, and it's what
drivers are doing today)

Sure, we can speed it up later if that appears to be necessary.

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