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

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Message-ID: <4A5626F2.7070404@garzik.org>
Date:	Thu, 09 Jul 2009 13:20:50 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Christoph Hellwig <hch@...radead.org>
CC:	Tejun Heo <tj@...nel.org>, Boaz Harrosh <bharrosh@...asas.com>,
	Jens Axboe <jens.axboe@...cle.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>,
	Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH 2/4] block: use the same failfast bits for bio and	request

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 :/

	Jeff




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