linux-kernel - Re: recent IDE regression

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Date:	Sat, 26 Jul 2008 14:13:38 +0200
From:	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ben Dooks <ben-linux@...ff.org>,
	David Miller <davem@...emloft.net>, harvey.harrison@...il.com,
	linux-ide@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: recent IDE regression

On Friday 25 July 2008, Linus Torvalds wrote:
> 
> On Fri, 25 Jul 2008, Ben Dooks wrote:
> > 
> > personally, i would much prefer to see the loop being less evil
> > like:
> > 
> > 	for (p = s; p < end; p += 2)
> > 		be16_to_cpus((u16 *)p);
> 
> Well, in this case, the code actually depends on 'p' being back at the 
> start of the buffer by the end of it all, so it would need some more 
> changes than that. 
> 
> But yes, I applied David's patch, but I _also_ suspect that we would be 
> better off without code that does horrid things like casts and assignments 
> inside the function arguments.
> 
> So it would be nice to re-code that loop to be more readable. But due to 
> the reliance of 'p' being 's' after the loop, the minimal patch would be 
> something like the appended.
> 
> Bartlomiej - take this or not, I'm not going to commit it - I haven't 
> tested it, nor do I even have any machines that would trigger it. So this 
> is more a "maybe something like this" than anything else.
> 
> 		Linus

Looks fine and I added it to pata tree but a test+ACK from
one of big-endianners would be great.

> ---
>  drivers/ide/ide-iops.c |    8 +++++---
>  1 files changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/ide/ide-iops.c b/drivers/ide/ide-iops.c
> index 8aae917..ae03151 100644
> --- a/drivers/ide/ide-iops.c
> +++ b/drivers/ide/ide-iops.c
> @@ -506,14 +506,16 @@ void ide_fix_driveid (struct hd_driveid *id)
>  
>  void ide_fixstring (u8 *s, const int bytecount, const int byteswap)
>  {
> -	u8 *p = s, *end = &s[bytecount & ~1]; /* bytecount must be even */
> +	u8 *p, *end = &s[bytecount & ~1]; /* bytecount must be even */
>  
>  	if (byteswap) {
>  		/* convert from big-endian to host byte order */
> -		for (p = end ; p != s;)
> -			be16_to_cpus((u16 *)(p -= 2));
> +		for (p = s ; p != end ; p += 2)
> +			be16_to_cpus((u16 *) p);
>  	}
> +
>  	/* strip leading blanks */
> +	p = s;
>  	while (s != end && *s == ' ')
>  		++s;
>  	/* compress internal blanks and strip trailing blanks */
--
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