linux-kernel - Re: idr_get_new

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Message-ID: <4C97BF0C.6070809@opengridcomputing.com>
Date:	Mon, 20 Sep 2010 15:07:40 -0500
From:	Steve Wise <swise@...ngridcomputing.com>
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 09/20/2010 02:31 PM, Andrew Morton wrote:
> 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.
>
>    

Looks ok to me also.  This is exactly what cxgb* needs.  IE the driver 
manages the ID space and never expects an idr insertion to fail because 
its already inserted.  That constitutes a driver bug (which is why the 
BUG_ON() is there :)).

Steve.

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