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Subject[PATCHv3] 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 <>
Signed-off-by: Tony Luck <>


v2 - fixes some checkpatch complaints about tabs/spaces/long-lines, and
more importantly fixes the problems that Arjan wants fixed (rather
than enabling him to apply the 2-liner to fix it).

v3 - Error code when hook is not present should be EINVAL, not ENODEV
for backwards compatability.

diff --git a/arch/x86/include/asm/mce.h b/arch/x86/include/asm/mce.h
index c9321f3..22cc0eb 100644
--- a/arch/x86/include/asm/mce.h
+++ b/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_hook(ssize_t (*)(struct file *filp,
+ const char __user *ubuf,
+ size_t usize, loff_t *off));

* Exception handler
diff --git a/arch/x86/kernel/cpu/mcheck/mce-inject.c b/arch/x86/kernel/cpu/mcheck/mce-inject.c
index 0ed633c..a18c2c8 100644
--- a/arch/x86/kernel/cpu/mcheck/mce-inject.c
+++ b/arch/x86/kernel/cpu/mcheck/mce-inject.c
@@ -215,7 +215,7 @@ 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_hook(mce_write);
return 0;
diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 08363b0..7010901 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -1628,16 +1628,35 @@ 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_hook(ssize_t (*fn)(struct file *filp,
+ const char __user *ubuf,
+ size_t usize, loff_t *off))
+ mce_write = fn;
+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,

static struct miscdevice mce_chrdev_device = {

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