linux-kernel - Re: [PATCH 2/4] block: use the same failfast bits for bio and request

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Message-ID: <20090709173900.GO23611@kernel.dk>
Date:	Thu, 9 Jul 2009 19:39:00 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	Christoph Hellwig <hch@...radead.org>, Tejun Heo <tj@...nel.org>,
	Boaz Harrosh <bharrosh@...asas.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	Niel Lambrechts <niel.lambrechts@...il.com>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Subject: Re: [PATCH 2/4] block: use the same failfast bits for bio and
	request

On Thu, Jul 09 2009, Jeff Garzik wrote:
> Christoph Hellwig wrote:
>> On Thu, Jul 09, 2009 at 09:45:24AM +0900, Tejun Heo wrote:
>>> What's more disturbing to me is the different between RQ and BIO
>>> flags.  __REQ_* are bit positions, REQ_* are masks while BIO_* are bit
>>> positions.  Sadly it seems it's already too late to change that.  I
>>> personally an not a big fan of simple accessors or flags defined as
>>> bit positions.  They seem to obscure things without much benefit.
>>
>> flags as bit positions generally only make sense if you use
>> test/set/clear_bit, otherwise they just confuse things.  And the
>> accessors are pretty annoying, especially in the block layer.  Trying to
>> find the places where a BIO flag has an actual effect is pretty painful
>> due to the mix of the different flags and the accessors.
>
> Indeed -- the accessors mean in practice that you always have at least  
> _two_ things to grep for, just to catch all accesses.  Block layer is  
> pretty bad about that style of usage :/

Yeah, I'm not too fond of it either, it does add to the confusion. I'll
sanitize it.

-- 
Jens Axboe

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