params: Add support for static keys

Static keys can now be a module parameter, e.g.

module_param_named(foo, foo.key, static_key_t, 0644)

bcachefs is now using this.

Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Petr Pavlu <petr.pavlu@suse.com>
Cc: Sami Tolvanen <samitolvanen@google.com>
Cc: Daniel Gomez <da.gomez@samsung.com>
Cc: linux-modules@vger.kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Author: Kent Overstreet

include/linux/jump_label.h

@@ -107,6 +107,8 @@ struct static_key {
 #endif	/* CONFIG_JUMP_LABEL */
 };
 
+typedef struct static_key static_key_t;
+
 #endif /* __ASSEMBLY__ */
 
 #ifdef CONFIG_JUMP_LABEL

include/linux/moduleparam.h

@@ -122,6 +122,7 @@ struct kparam_array
  *	charp: a character pointer
  *	bool: a bool, values 0/1, y/n, Y/N.
  *	invbool: the above, only sense-reversed (N = true).
+ *	static_key_t: same as bool, but updates a 'struct static_key'
  */
 #define module_param(name, type, perm)				\
 	module_param_named(name, name, type, perm)
@@ -488,6 +489,12 @@ 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 static key, which can only be set like a bool */
+extern const struct kernel_param_ops param_ops_static_key_t;
+extern int param_set_static_key_t(const char *val, const struct kernel_param *kp);
+extern int param_get_static_key_t(char *buffer, const struct kernel_param *kp);
+#define param_check_static_key_t(name, p) __param_check(name, p, struct static_key)
+
 /**
  * module_param_array - a parameter which is an array of some type
  * @name: the name of the array variable

kernel/params.c

@@ -14,6 +14,7 @@
 #include <linux/overflow.h>
 #include <linux/security.h>
 #include <linux/slab.h>
+#include <linux/static_key.h>
 #include <linux/string.h>
 
 #ifdef CONFIG_SYSFS
@@ -412,6 +413,40 @@ const struct kernel_param_ops param_ops_bint = {
 };
 EXPORT_SYMBOL(param_ops_bint);
 
+int param_set_static_key_t(const char *val, const struct kernel_param *kp)
+{
+	/* Match bool exactly, by re-using it. */
+	struct kernel_param boolkp = *kp;
+	bool v;
+	int ret;
+
+	boolkp.arg = &v;
+
+	ret = param_set_bool(val, &boolkp);
+	if (ret)
+		return ret;
+	if (v)
+		static_key_enable(kp->arg);
+	else
+		static_key_disable(kp->arg);
+	return 0;
+}
+EXPORT_SYMBOL(param_set_static_key_t);
+
+int param_get_static_key_t(char *buffer, const struct kernel_param *kp)
+{
+	struct static_key *key = kp->arg;
+	return sprintf(buffer, "%c\n", static_key_enabled(key) ? 'Y' : 'N');
+}
+EXPORT_SYMBOL(param_get_static_key_t);
+
+const struct kernel_param_ops param_ops_static_key_t = {
+	.flags = KERNEL_PARAM_OPS_FL_NOARG,
+	.set = param_set_static_key_t,
+	.get = param_get_static_key_t,
+};
+EXPORT_SYMBOL(param_ops_static_key_t);
+
 /* We break the rule and mangle the string. */
 static int param_array(struct module *mod,
 		       const char *name,