The maximum module name length (MODULE_NAME_LEN) is somewhat confusingly
defined in terms of the maximum parameter prefix length
(MAX_PARAM_PREFIX_LEN), when in fact the dependency is in the opposite
direction.

This split originates from commit 730b69d22525 ("module: check kernel param
length at compile time, not runtime"). The code needed to use
MODULE_NAME_LEN in moduleparam.h, but because module.h requires
moduleparam.h, this created a circular dependency. It was resolved by
introducing MAX_PARAM_PREFIX_LEN in moduleparam.h and defining
MODULE_NAME_LEN in module.h in terms of MAX_PARAM_PREFIX_LEN.

Rename MAX_PARAM_PREFIX_LEN to __MODULE_NAME_LEN for clarity. This matches
the similar approach of defining MODULE_INFO in module.h and __MODULE_INFO
in moduleparam.h.

Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
---
 include/linux/module.h      |  2 +-
 include/linux/moduleparam.h | 12 ++++++++----
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/include/linux/module.h b/include/linux/module.h
index 5faa1fb1f4b4..0f1dde3996d9 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -32,7 +32,7 @@
 #include <linux/percpu.h>
 #include <asm/module.h>
 
-#define MODULE_NAME_LEN MAX_PARAM_PREFIX_LEN
+#define MODULE_NAME_LEN __MODULE_NAME_LEN
 
 struct modversion_info {
 	unsigned long crc;
diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index 110e9d09de24..a04a2bc4f51e 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -6,6 +6,13 @@
 #include <linux/stringify.h>
 #include <linux/kernel.h>
 
+/*
+ * The maximum module name length, including the NUL byte.
+ * Chosen so that structs with an unsigned long line up, specifically
+ * modversion_info.
+ */
+#define __MODULE_NAME_LEN (64 - sizeof(unsigned long))
+
 /* You can override this manually, but generally this should match the
    module name. */
 #ifdef MODULE
@@ -17,9 +24,6 @@
 #define __MODULE_INFO_PREFIX KBUILD_MODNAME "."
 #endif
 
-/* Chosen so that structs with an unsigned long line up. */
-#define MAX_PARAM_PREFIX_LEN (64 - sizeof(unsigned long))
-
 #define __MODULE_INFO(tag, name, info)					  \
 	static const char __UNIQUE_ID(name)[]				  \
 		__used __section(".modinfo") __aligned(1)		  \
@@ -284,7 +288,7 @@ struct kparam_array
 
 /* This is the fundamental function for registering boot/module parameters. */
 #define __module_param_call(prefix, name, ops, arg, perm, level, flags)	\
-	static_assert(sizeof(""prefix) - 1 <= MAX_PARAM_PREFIX_LEN);	\
+	static_assert(sizeof(""prefix) - 1 <= __MODULE_NAME_LEN);	\
 	static const char __param_str_##name[] = prefix #name;		\
 	static struct kernel_param __moduleparam_const __param_##name	\
 	__used __section("__param")					\
-- 
2.49.0

On 30/06/2025 16.32, Petr Pavlu wrote:
> The maximum module name length (MODULE_NAME_LEN) is somewhat confusingly
> defined in terms of the maximum parameter prefix length
> (MAX_PARAM_PREFIX_LEN), when in fact the dependency is in the opposite
> direction.
> 
> This split originates from commit 730b69d22525 ("module: check kernel param
> length at compile time, not runtime"). The code needed to use
> MODULE_NAME_LEN in moduleparam.h, but because module.h requires
> moduleparam.h, this created a circular dependency. It was resolved by
> introducing MAX_PARAM_PREFIX_LEN in moduleparam.h and defining
> MODULE_NAME_LEN in module.h in terms of MAX_PARAM_PREFIX_LEN.
> 
> Rename MAX_PARAM_PREFIX_LEN to __MODULE_NAME_LEN for clarity. This matches
> the similar approach of defining MODULE_INFO in module.h and __MODULE_INFO
> in moduleparam.h.
> 
> Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
> ---
>  include/linux/module.h      |  2 +-
>  include/linux/moduleparam.h | 12 ++++++++----
>  2 files changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 5faa1fb1f4b4..0f1dde3996d9 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -32,7 +32,7 @@
>  #include <linux/percpu.h>
>  #include <asm/module.h>
>  
> -#define MODULE_NAME_LEN MAX_PARAM_PREFIX_LEN
> +#define MODULE_NAME_LEN __MODULE_NAME_LEN
>  
>  struct modversion_info {
>  	unsigned long crc;
> diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
> index 110e9d09de24..a04a2bc4f51e 100644
> --- a/include/linux/moduleparam.h
> +++ b/include/linux/moduleparam.h
> @@ -6,6 +6,13 @@
>  #include <linux/stringify.h>
>  #include <linux/kernel.h>
>  
> +/*
> + * The maximum module name length, including the NUL byte.
> + * Chosen so that structs with an unsigned long line up, specifically
> + * modversion_info.
> + */
> +#define __MODULE_NAME_LEN (64 - sizeof(unsigned long))
> +
>  /* You can override this manually, but generally this should match the
>     module name. */
>  #ifdef MODULE
> @@ -17,9 +24,6 @@
>  #define __MODULE_INFO_PREFIX KBUILD_MODNAME "."
>  #endif
>  
> -/* Chosen so that structs with an unsigned long line up. */
> -#define MAX_PARAM_PREFIX_LEN (64 - sizeof(unsigned long))
> -
>  #define __MODULE_INFO(tag, name, info)					  \
>  	static const char __UNIQUE_ID(name)[]				  \
>  		__used __section(".modinfo") __aligned(1)		  \
> @@ -284,7 +288,7 @@ struct kparam_array
>  
>  /* This is the fundamental function for registering boot/module parameters. */
>  #define __module_param_call(prefix, name, ops, arg, perm, level, flags)	\
> -	static_assert(sizeof(""prefix) - 1 <= MAX_PARAM_PREFIX_LEN);	\
> +	static_assert(sizeof(""prefix) - 1 <= __MODULE_NAME_LEN);	\
>  	static const char __param_str_##name[] = prefix #name;		\
>  	static struct kernel_param __moduleparam_const __param_##name	\
>  	__used __section("__param")					\


LGTM,

Reviewed-by: Daniel Gomez <da.gomez@samsung.com>