Re: [dm-devel] idr_get_new_exact ?

[Andrew Morton <akpm linux-foundation org>]

On Mon, 20 Sep 2010 16:11:31 +0200
Ohad Ben-Cohen <ohad wizery com> 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.