linux-kernel - Re: [RFC 1/6] bidi support: request dma_data

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Date:	Tue, 23 Jan 2007 17:17:19 +0200
From:	Benny Halevy <bhalevy@...asas.com>
To:	Muli Ben-Yehuda <muli@...ibm.com>
CC:	Boaz Harrosh <bharrosh@...asas.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Mike Christie <michaelc@...wisc.edu>,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	open-iscsi@...glegroups.com, Daniel.E.Messinger@...gate.com,
	Liran Schour <LIRANS@...ibm.com>
Subject: Re: [RFC 1/6] bidi support: request dma_data_direction

Muli Ben-Yehuda wrote:
> On Tue, Jan 23, 2007 at 03:45:00PM +0200, Benny Halevy wrote:
> 
>>>> +static inline int dma_uni_dir(enum dma_data_direction dir)
>>>> +{
>>>> +	return (dir == DMA_TO_DEVICE) || (dir == DMA_FROM_DEVICE) ||
>>>> +	       (dir == DMA_NONE);
>>>> +}
>>> While this doesn't look very useful. Why is "DMA_NONE" a uni-dir? I
>>> suggest replacing this with an open coded (dir != DMA_BIDIRECTIONAL).
>> The idea was to be resilient to invalid values. (dir != DMA_BIDIRECTIONAL)
>> is fine of course, but I'd add a BUG_ON such as (dir < 0 || dir >
>> DMA_BIDIRECTIONAL)
> 
> If DMA_NONE isn't actually allowed here, you can use valid_dma_direction().

DMA_NONE should be allowed as it is used by commands that do no I/O and these
are handled on uni-directional path.

BTW, the BUG_ON I suggested has a bug of course since (countering my intuition)
DMA_BIDIRECTIONAL==0, so it should be BUG_ON(dir < 0 || dir > DMA_NONE)
instead.
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