linux-kernel - Re: [PATCH] libata: fallback to the other IDENTIFY on device error, take#2

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Date:	Sun, 13 May 2007 19:50:16 +0200
From:	Tejun Heo <htejun@...il.com>
To:	Dave Jones <davej@...hat.com>, Tejun Heo <htejun@...il.com>,
	Jeff Garzik <jeff@...zik.org>,
	William Thompson <wt@...ctro-mechanical.com>,
	Mark Lord <liml@....ca>, linux-kernel@...r.kernel.org,
	IDE/ATA development list <linux-ide@...r.kernel.org>,
	albertcc@...ibm.com
Subject: Re: [PATCH] libata: fallback to the other IDENTIFY on device error,
 take#2

Dave Jones wrote:
> On Sun, May 13, 2007 at 02:57:44PM +0200, Tejun Heo wrote:
>  > Jeff Garzik wrote:
>  > > Tejun Heo wrote:
>  > >> +            if (class == ATA_DEV_ATA)
>  > >> +                class = ATA_DEV_ATAPI;
>  > >> +            else
>  > >> +                class = ATA_DEV_ATA;
>  > > 
>  > > 
>  > > the 'else' branch is obviously redundant
>  > 
>  > Why?  We can also fallback from ATAPI to ATA.
> 
> Then did you mean to write..
> 
> +            if (class == ATA_DEV_ATA)
> +                class = ATA_DEV_ATAPI;
> +            else if (class == ATA_DEV_ATAPI)
> +                class = ATA_DEV_ATA;
> 
> ?
> 
> Otherwise, as Jeff mentions, you're doing a redundant assignment
> in the else branch.

Hmmm... I'm feeling very dense today.  At that point, class is either
ATA_DEV_ATA or ATA_DEV_ATAPI.  The if-else clause tries to flip between
the two.

1. if class == ATA_DEV_ATA, the 'if' test succeeds and "class =
ATA_DEV_ATAPI" runs, so it flips correctly.

2. if class == ATA_DEV_ATAPI,  the 'if' test fails and "class =
ATA_DEV_ATA" runs, so it flips correctly.

What am I missing here?  Feel free to scream at me and hammer me into
senses.  :-)

-- 
tejun
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