x86/mce: Make mce_chrdev_ops 'static const'

Arjan would like to make struct file_operations const, but
mce-inject directly writes to the mce_chrdev_ops to install its
write handler. In an ideal world mce-inject would have its own
character device, but we have a sizable legacy of test scripts
that hardwire "/dev/mcelog", so it would be painful to switch to
a separate device now. Instead, this patch switches to a stub
function in the mce code, with a registration helper that
mce-inject can call when it is loaded.

Note that this would also allow for a sane process to allow
mce-inject to be unloaded again (with an unregister function,
and appropriate module_{get,put}() calls), but that is left for
potential future patches.

Reported-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Link: http://lkml.kernel.org/r/4eb2e1971326651a3b@agluck-desktop.sc.intel.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/include/asm/mce.h

@@ -201,7 +201,10 @@ int mce_notify_irq(void);
 void mce_notify_process(void);
 
 DECLARE_PER_CPU(struct mce, injectm);
-extern struct file_operations mce_chrdev_ops;
+
+extern void register_mce_write_callback(ssize_t (*)(struct file *filp,
+				    const char __user *ubuf,
+				    size_t usize, loff_t *off));
 
 /*
  * Exception handler