linux-kernel - Re: [PATCH 10/19] workqueue: update cwq alignement and make one more flag bit available

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Message-ID: <4AC4D595.2070202@garzik.org>
Date:	Thu, 01 Oct 2009 12:15:17 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	David Howells <dhowells@...hat.com>
CC:	Tejun Heo <tj@...nel.org>, mingo@...e.hu,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	jens.axboe@...cle.com, rusty@...tcorp.com.au,
	cl@...ux-foundation.org, arjan@...ux.intel.com
Subject: Re: [PATCH 10/19] workqueue: update cwq alignement and make one more
 flag bit available

On 10/01/2009 09:05 AM, David Howells wrote:
> Tejun Heo<tj@...nel.org>  wrote:
>
>> +enum {
>> +	WORK_STRUCT_PENDING	= 0,	/* work item is pending execution */
>> +
>> +	/*
>> +	 * Reserve 3bits off of cwq pointer.  This is enough and
>> +	 * provides acceptable alignment on both 32 and 64bit
>> +	 * machines.
>> +	 */
>> +	WORK_STRUCT_FLAG_BITS	= 3,
>> +
>> +	WORK_STRUCT_FLAG_MASK	= (1UL<<  WORK_STRUCT_FLAG_BITS) - 1,
>> +	WORK_STRUCT_WQ_DATA_MASK = ~WORK_STRUCT_FLAG_MASK,
>> +};
>
> There's some great enum abuse going on here:-)

The quoted code is a standard kernel technique for creating typed 
constants that are visible to the C compiler (rather than CPP) and debugger.

It is found in a great many Linux kernel drivers at this point, and is 
definitely not abuse, IMO.

	Jeff


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