linux-kernel - Re: idr_get_new

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Message-Id: <20100920123140.f524de79.akpm@linux-foundation.org>
Date:	Mon, 20 Sep 2010 12:31:40 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ohad Ben-Cohen <ohad@...ery.com>
Cc:	linux-kernel@...r.kernel.org,
	"Jean Delvare (PC drivers, core)" <khali@...ux-fr.org>,
	"Ben Dooks (embedded platforms)" <ben-linux@...ff.org>,
	Roland Dreier <rolandd@...co.com>,
	Sean Hefty <sean.hefty@...el.com>,
	Hal Rosenstock <hal.rosenstock@...il.com>,
	Steve Wise <swise@...lsio.com>, Neil Brown <neilb@...e.de>,
	Paul Mackerras <paulus@...ba.org>, linux-i2c@...r.kernel.org,
	linux-rdma@...r.kernel.org, dm-devel@...hat.com,
	linux-raid@...r.kernel.org, linux-ppp@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: idr_get_new_exact ?

On Mon, 20 Sep 2010 16:11:31 +0200
Ohad Ben-Cohen <ohad@...ery.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.

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