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

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Message-ID: <xeivxiix7dk2bmht22xeocmluom4nkcel35qa672mm52cq2ynx@rago3au3x6dy>
Date: Tue, 13 May 2025 09:06:41 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Petr Pavlu <petr.pavlu@...e.com>
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 Mon, May 12, 2025 at 03:51:00PM +0200, Petr Pavlu wrote:
> 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.

Thanks, fixed these