fix /proc/vmcore seek

[Arnd Bergmann]

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.

--- 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)