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>

2 files changed, 23 insertions, 4 deletions

diff --git a/arch/x86/kernel/cpu/mcheck/mce-inject.c b/arch/x86/kernel/cpu/mcheck/mce-inject.c
index 6199232161cf..319882ef848d 100644
--- a/arch/x86/kernel/cpu/mcheck/mce-inject.c
+++ b/arch/x86/kernel/cpu/mcheck/mce-inject.c
@@ -208,7 +208,7 @@ static int inject_init(void)
         if (!alloc_cpumask_var(&mce_inject_cpumask, GFP_KERNEL))
                 return -ENOMEM;
         printk(KERN_INFO "Machine check injector initialized\n");
-        mce_chrdev_ops.write = mce_write;
+        register_mce_write_callback(mce_write);
         register_nmi_handler(NMI_LOCAL, mce_raise_notify, 0,
                                 "mce_notify");
         return 0;
diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 362056aefeb4..2af127d4c3d1 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -1634,16 +1634,35 @@ static long mce_chrdev_ioctl(struct file *f, unsigned int cmd,
         }
 }
 
-/* Modified in mce-inject.c, so not static or const */
-struct file_operations mce_chrdev_ops = {
+static ssize_t (*mce_write)(struct file *filp, const char __user *ubuf,
+                            size_t usize, loff_t *off);
+
+void register_mce_write_callback(ssize_t (*fn)(struct file *filp,
+                             const char __user *ubuf,
+                             size_t usize, loff_t *off))
+{
+        mce_write = fn;
+}
+EXPORT_SYMBOL_GPL(register_mce_write_callback);
+
+ssize_t mce_chrdev_write(struct file *filp, const char __user *ubuf,
+                         size_t usize, loff_t *off)
+{
+        if (mce_write)
+                return mce_write(filp, ubuf, usize, off);
+        else
+                return -EINVAL;
+}
+
+static const struct file_operations mce_chrdev_ops = {
         .open                   = mce_chrdev_open,
         .release                = mce_chrdev_release,
         .read                   = mce_chrdev_read,
+        .write                  = mce_chrdev_write,
         .poll                   = mce_chrdev_poll,
         .unlocked_ioctl         = mce_chrdev_ioctl,
         .llseek                 = no_llseek,
 };
-EXPORT_SYMBOL_GPL(mce_chrdev_ops);
 
 static struct miscdevice mce_chrdev_device = {
         MISC_MCELOG_MINOR,