[PATCH 0/4] treewide: Make definitions of struct kernel_param_ops const

[PATCH 0/4] treewide: Make definitions of struct kernel_param_ops const

[Joe Perches]

Using const is good as it reduces data size.

Joe Perches (4):
  KVM: PPC: Book3S HV: Make struct kernel_param_ops definition const
  kvm x86/mmu: Make struct kernel_param_ops definitions const
  rcu/tree: Make struct kernel_param_ops definitions const
  mm/zswap: Make struct kernel_param_ops definitions const

 arch/powerpc/kvm/book3s_hv.c | 2 +-
 arch/x86/kvm/mmu/mmu.c       | 4 ++--
 kernel/rcu/tree.c            | 4 ++--
 mm/zswap.c                   | 6 +++---
 4 files changed, 8 insertions(+), 8 deletions(-)

-- 
2.26.0

[PATCH 4/4] mm/zswap: Make struct kernel_param_ops definitions const

[Joe Perches]

These should be const, so make it so.

Signed-off-by: Joe Perches <joe@perches.com>
---
 mm/zswap.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index fbb782924ccc..1eced701b3bd 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -81,7 +81,7 @@ static bool zswap_pool_reached_full;
 static bool zswap_enabled = IS_ENABLED(CONFIG_ZSWAP_DEFAULT_ON);
 static int zswap_enabled_param_set(const char *,
 				   const struct kernel_param *);
-static struct kernel_param_ops zswap_enabled_param_ops = {
+static const struct kernel_param_ops zswap_enabled_param_ops = {
 	.set =		zswap_enabled_param_set,
 	.get =		param_get_bool,
 };
@@ -91,7 +91,7 @@ module_param_cb(enabled, &zswap_enabled_param_ops, &zswap_enabled, 0644);
 static char *zswap_compressor = CONFIG_ZSWAP_COMPRESSOR_DEFAULT;
 static int zswap_compressor_param_set(const char *,
 				      const struct kernel_param *);
-static struct kernel_param_ops zswap_compressor_param_ops = {
+static const struct kernel_param_ops zswap_compressor_param_ops = {
 	.set =		zswap_compressor_param_set,
 	.get =		param_get_charp,
 	.free =		param_free_charp,
@@ -102,7 +102,7 @@ module_param_cb(compressor, &zswap_compressor_param_ops,
 /* Compressed storage zpool to use */
 static char *zswap_zpool_type = CONFIG_ZSWAP_ZPOOL_DEFAULT;
 static int zswap_zpool_param_set(const char *, const struct kernel_param *);
-static struct kernel_param_ops zswap_zpool_param_ops = {
+static const struct kernel_param_ops zswap_zpool_param_ops = {
 	.set =		zswap_zpool_param_set,
 	.get =		param_get_charp,
 	.free =		param_free_charp,
-- 
2.26.0

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

[Joe Perches]

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@perches.com/T/

Anyone know if it's appropriate to change the
sprintf-like uses in these functions to sysfs_emit
and/or sysfs_emit_at?

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

[Matthew Wilcox]

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@perches.com/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.

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@perches.com/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)			\