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

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Message-ID: <84e82d74-312f-4c6c-b197-b44e59e9470c@suse.com>
Date: Mon, 12 May 2025 15:51:00 +0200
From: Petr Pavlu <petr.pavlu@...e.com>
To: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: linux-kernel@...r.kernel.org, Luis Chamberlain <mcgrof@...nel.org>,
 Sami Tolvanen <samitolvanen@...gle.com>, Daniel Gomez
 <da.gomez@...sung.com>, linux-modules@...r.kernel.org
Subject: Re: [PATCH] params: Add support for static keys

On 5/10/25 23:01, Kent Overstreet wrote:
> 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

Please Cc also the "STATIC BRANCH/CALL" folks on the next version.

> 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

The module_param() macro in this file has a kernel-doc that describes
all currently supported standard types:

 * Standard types are:
 *	byte, hexint, short, ushort, int, uint, long, ulong
 *	charp: a character pointer
 *	bool: a bool, values 0/1, y/n, Y/N.
 *	invbool: the above, only sense-reversed (N = true).

The static_key_t should be added to this list.

> @@ -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');

The 'N'/'Y' values are the other way around.

> +}
> +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,

-- 
Thanks
Petr