linux-kernel - [PATCH] params: Add support for static keys

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Message-ID: <20250510210126.4032840-1-kent.overstreet@linux.dev>
Date: Sat, 10 May 2025 17:01:26 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: linux-kernel@...r.kernel.org
Cc: Kent Overstreet <kent.overstreet@...ux.dev>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Petr Pavlu <petr.pavlu@...e.com>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	Daniel Gomez <da.gomez@...sung.com>,
	linux-modules@...r.kernel.org
Subject: [PATCH] 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@...nel.org>
Cc: Petr Pavlu <petr.pavlu@...e.com>
Cc: Sami Tolvanen <samitolvanen@...gle.com>
Cc: Daniel Gomez <da.gomez@...sung.com>
Cc: linux-modules@...r.kernel.org
Signed-off-by: Kent Overstreet <kent.overstreet@...ux.dev>
---
 include/linux/jump_label.h  |  2 ++
 include/linux/moduleparam.h |  6 ++++++
 kernel/params.c             | 35 +++++++++++++++++++++++++++++++++++
 3 files changed, 43 insertions(+)

diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index fdb79dd1ebd8..0fc9b71db56f 100644
--- a/include/linux/jump_label.h
+++ b/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
diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index bfb85fd13e1f..2494e7e67453 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -488,6 +488,12 @@ 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
diff --git a/kernel/params.c b/kernel/params.c
index 2509f216c9f3..991f49e138e7 100644
--- a/kernel/params.c
+++ b/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) ? 'N' : 'Y');
+}
+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,
-- 
2.49.0