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module: Clarify documentation of module_param_call()

PATCH Superseded Kees Cook 2 participants 2 messages Sep 5, 2023 Module support

v1 of 2 Superseded Latest is v2 →

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Kees Cook

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#0 lore raw

PATCH 1/1 module: Clarify documentation of module_param_call()

Commit 9bbb9e5a3310 ("param: use ops in struct kernel_param, rather than get and set fns directly") added the comment that module_param_call() was deprecated, during a large scale refactoring to bring sanity to type casting back then. In 2017 following more cleanups, it became useful against as it wraps a common pattern of creating an ops struct for a given get/set pair:

b2f270e87473 ("module: Prepare to convert all module_param_call() prototypes") ece1996a21ee ("module: Do not paper over type mismatches in module_param_call()")

        static const struct kernel_param_ops __param_ops_##name = \
                { .flags = 0, .set = _set, .get = _get }; \
        __module_param_call(MODULE_PARAM_PREFIX, \
                            name, &__param_ops_##name, arg, perm, -1, 0)

        __module_param_call(MODULE_PARAM_PREFIX, name, ops, arg, perm, -1, 0)

Many users of module_param_cb() appear to be almost universally open-coding the same thing that module_param_call() does now. Don't discourage[1] people from using module_param_call() but clarifying the
comment: module_param_cb() is useful if you repeatedly use the same pair of get/set functions.

[1] https://lore.kernel.org/lkml/202308301546.5C789E5EC@keescook/

Cc Luis Chamberlain <[email protected]>
Cc Johan Hovold <[email protected]>
Cc Jessica Yu <[email protected]>
Cc Sagi Grimberg <[email protected]>
Cc Nick Desaulniers <[email protected]>
Cc Miguel Ojeda <[email protected]>
Cc Joe Perches <[email protected]>
Cc Azeem Shaikh <[email protected]>
Cc [email protected]
Signed-off-by Kees Cook <[email protected]>

---
Luis, I note that include/linux/moduleparam.h isn't in the MAINTAINERS file pattern. Perhaps you want to use include/linux/module*.h?

---
 include/linux/moduleparam.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
include/linux/moduleparam.h +1 -1
index 962cd41a2cb5..d32450583182 100644
@@ -293,7 +293,7 @@ struct kparam_array
 	= { __param_str_##name, THIS_MODULE, ops,			\
 	    VERIFY_OCTAL_PERMISSIONS(perm), level, flags, { arg } }
 
-/* Obsolete - use module_param_cb() */
+/* For repeated _set & _get usage use module_param_cb() */
 #define module_param_call(name, _set, _get, arg, perm)			\
 	static const struct kernel_param_ops __param_ops_##name =	\
 		{ .flags = 0, .set = _set, .get = _get };		\
Signature · 1 line
2.34.1
Reviewed-by on v1 1/1
#1 lore raw
Quoted 6 lines · Kees Cook

Commit 9bbb9e5a3310 ("param: use ops in struct kernel_param, rather than get and set fns directly") added the comment that module_param_call() was deprecated, during a large scale refactoring to bring sanity to type casting back then. In 2017 following more cleanups, it became useful against as it wraps a common pattern of creating an ops struct for a

s/against/again/

Quoted 5 lines

Many users of module_param_cb() appear to be almost universally open-coding the same thing that module_param_call() does now. Don't discourage[1] people from using module_param_call() but clarifying the
comment: module_param_cb() is useful if you repeatedly use the same pair of get/set functions.

s/clarifying/clarify/

I sampled some, and indeed many define the ops struct.

Quoted 1 line

[1] https://lore.kernel.org/lkml/202308301546.5C789E5EC@keescook/

Link tag here? It is actually quite nicely explained there.

include/linux/moduleparam.h struct kparam_array · line 296

Quoted 2 lines
include/linux/moduleparam.h +1 -1
-/* Obsolete - use module_param_cb() */
+/* For repeated _set & _get usage use module_param_cb() */

Perhaps add "instead"? Or perhaps add a bit more detail, something like:

Useful for describing a set/get pair used only once (i.e. for this
parameter). For repeated set/get pairs (i.e. the same kernel_param_ops struct), use module_param_cb() instead.

Reviewed-by Miguel Ojeda <[email protected]>

Cheers,
Miguel