fix /proc/vmcore seek

[CAI Qian]

----- "Arnd Bergmann" <arnd at arndb.de> wrote:

> Commit 73296bc611 "procfs: Use generic_file_llseek in /proc/vmcore"
> broke
> seeking on /proc/vmcore. This changes it back to use default_llseek
> in order to restore the original behaviour.
> 
> Signed-off-by: Arnd Bergmann <arnd at arndb.de>
> Cc: Frederic Weisbecker <fweisbec at gmail.com>
> Cc: stable at kernel.org
> 
> ---
> On Thursday 02 September 2010, CAI Qian wrote:
> > 
> > Ken'ichi, it turned out this kernel patch caused makedumpfile
> failure below.
> > I am not sure if this is a kernel bug or makedumpfile needs to catch
> up with
> > the change.
> 
> It doesn't matter who is correct here. A user program regressed
> because of a
> kernel change, so we need to fix the kernel. Thanks for the report!
> 
> Please try this patch.
Confirmed makedumpfile is working again after applied this patch.
> --- a/fs/proc/vmcore.c
> +++ b/fs/proc/vmcore.c
> @@ -163,7 +163,7 @@ static ssize_t read_vmcore(struct file *file, char
> __user *buffer,
>  
>  static const struct file_operations proc_vmcore_operations = {
>  	.read		= read_vmcore,
> -	.llseek		= generic_file_llseek,
> +	.llseek		= default_llseek,
>  };
>  
>  static struct vmcore* __init get_new_element(void)
> 
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