linux-kernel - Re: [PATCH] /dev/mem: Allow rewinding

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Date:	Tue, 6 Apr 2010 13:15:20 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Dave Jones <davej@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH] /dev/mem: Allow rewinding

On Tue, Apr 06, 2010 at 05:19:05AM +0800, Eric Dumazet wrote:
> Le lundi 05 avril 2010 à 23:04 +0200, Eric Dumazet a écrit :
> > Andrew, commit dcefafb6ac90ece8d68a6c203105f3d313e52da4 seems to be the
> > problem. 
> > 
> > It breaks rewinds (negative offsets to lseek (... SEEK_CUR))
> > 
> 
> Here is a patch to make rewind working again on /dev/mem

Looks good to me. Thanks for the fix!

Thanks,
Fengguang

> [PATCH] /dev/mem: Allow rewinding
> 
> commit dcefafb6 (/dev/mem: dont allow seek to last page)
> inadvertently disabled rewinding on /dev/mem.
> 
> This broke x86info for example.
> 
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> ---
> diff --git a/drivers/char/mem.c b/drivers/char/mem.c
> index 1f3215a..3973a1d 100644
> --- a/drivers/char/mem.c
> +++ b/drivers/char/mem.c
> @@ -710,11 +710,6 @@ static loff_t memory_lseek(struct file *file, loff_t offset, int orig)
>  	switch (orig) {
>  	case SEEK_CUR:
>  		offset += file->f_pos;
> -		if ((unsigned long long)offset <
> -		    (unsigned long long)file->f_pos) {
> -			ret = -EOVERFLOW;
> -			break;
> -		}
>  	case SEEK_SET:
>  		/* to avoid userland mistaking f_pos=-9 as -EBADF=-9 */
>  		if ((unsigned long long)offset >= ~0xFFFULL) {
> 
> 
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