[PATCH 1/2] params: Add a per cpu module param type

[Andi Kleen <andi@firstfloor.org>]

From: Andi Kleen <ak@linux.intel.com>

This is mainly useful for simple statistic counters.
Essentially read-only, writing only clears.

Cc: rusty@rustcorp.com.au
Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
 include/linux/moduleparam.h |  4 ++++
 kernel/params.c             | 28 ++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index 494f99e..d019ad2 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -408,6 +408,10 @@ extern int param_set_bint(const char *val, const struct kernel_param *kp);
 #define param_get_bint param_get_int
 #define param_check_bint param_check_int
 
+/* A per cpu read-only unsigned integer. Useful for counters. */
+extern struct kernel_param_ops param_ops_percpu_uint;
+#define param_check_percpu_uint(name, p) param_check_uint
+
 /**
  * module_param_array - a parameter which is an array of some type
  * @name: the name of the array variable
diff --git a/kernel/params.c b/kernel/params.c
index 34f5270..700badd 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -499,6 +499,34 @@ struct kernel_param_ops param_ops_string = {
 };
 EXPORT_SYMBOL(param_ops_string);
 
+/* Per CPU read only module param. */
+
+static int param_percpu_uint_set(const char *val, const struct kernel_param *kp)
+{
+	int cpu;
+
+	/* just clear on any write */
+	for_each_possible_cpu(cpu)
+		*per_cpu_ptr((unsigned * __percpu)(kp->arg), cpu) = 0;
+	return 0;
+}
+
+static int param_percpu_uint_get(char *buffer, const struct kernel_param *kp)
+{
+	int cpu;
+	unsigned count = 0;
+
+	for_each_possible_cpu(cpu)
+		count += *per_cpu_ptr((unsigned * __percpu)(kp->arg), cpu);
+	return sprintf(buffer, "%u", count);
+}
+
+struct kernel_param_ops param_ops_percpu_uint = {
+	.set = param_percpu_uint_set,
+	.get = param_percpu_uint_get,
+};
+EXPORT_SYMBOL(param_ops_percpu_uint);
+
 /* sysfs output in /sys/modules/XYZ/parameters/ */
 #define to_module_attr(n) container_of(n, struct module_attribute, attr)
 #define to_module_kobject(n) container_of(n, struct module_kobject, kobj)
-- 
1.9.3