Re: Where is the declaration of buffer used in kernel_param_ops .get functions?

[Joe Perches]

On Sun, 2020-10-04 at 02:36 +0100, Matthew Wilcox wrote:
> On Sat, Oct 03, 2020 at 06:19:18PM -0700, Joe Perches wrote:
> > These patches came up because I was looking for
> > the location of the declaration of the buffer used
> > in kernel/params.c struct kernel_param_ops .get
> > functions.
> > 
> > I didn't find it.
> > 
> > I want to see if it's appropriate to convert the
> > sprintf family of functions used in these .get
> > functions to sysfs_emit.
> > 
> > Patches submitted here:
> > https://lore.kernel.org/lkml/5d606519698ce4c8f1203a2b35797d8254c6050a.1600285923.git.joe@xxxxxxxxxxx/T/
> > 
> > Anyone know if it's appropriate to change the
> > sprintf-like uses in these functions to sysfs_emit
> > and/or sysfs_emit_at?
> 
> There's a lot of preprocessor magic to wade through.
> 
> I'm pretty sure this comes through include/linux/moduleparam.h
> and kernel/module.c.

Dunno, looked there, still can't find it.

btw:

The __module_param_call macro looks very dodgy
as it uses both __used and __attribute__((unused))
and likely one of them should be removed (unused?)

It looks like the comes from varying definitions of
__attribute_used__ eventually converted to __used 
for old gcc versions 2, 3, and 4.

1da177e4c3f4:include/linux/compiler-gcc2.h:#define __attribute_used__   __attribute__((__unused__))
1da177e4c3f4:include/linux/compiler-gcc3.h:# define __attribute_used__  __attribute__((__used__))
1da177e4c3f4:include/linux/compiler-gcc3.h:# define __attribute_used__  __attribute__((__unused__))
1da177e4c3f4:include/linux/compiler-gcc4.h:#define __attribute_used__   __attribute__((__used__))

Maybe:

---
 include/linux/moduleparam.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index 47879fc7f75e..fc820b27fb00 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -288,10 +288,10 @@ struct kparam_array
 	/* Default value instead of permissions? */			\
 	static const char __param_str_##name[] = prefix #name;		\
 	static struct kernel_param __moduleparam_const __param_##name	\
-	__used								\
-    __attribute__ ((unused,__section__ ("__param"),aligned(sizeof(void *)))) \
-	= { __param_str_##name, THIS_MODULE, ops,			\
-	    VERIFY_OCTAL_PERMISSIONS(perm), level, flags, { arg } }
+	__used __section("__param") __aligned(sizeof(void *)) = {	\
+		__param_str_##name, THIS_MODULE, ops,			\
+		VERIFY_OCTAL_PERMISSIONS(perm), level, flags, { arg }	\
+	}
 
 /* Obsolete - use module_param_cb() */
 #define module_param_call(name, _set, _get, arg, perm)			\