Re: [PATCH v4 12/17] slab: create kmem_cache_create() compatibility layer

[Mike Rapoport <rppt@kernel.org>]

On Thu, Sep 05, 2024 at 09:56:55AM +0200, Christian Brauner wrote:
> Use _Generic() to create a compatibility layer that type switches on the
> third argument to either call __kmem_cache_create() or
> __kmem_cache_create_args(). If NULL is passed for the struct
> kmem_cache_args argument use default args making porting for callers
> that don't care about additional arguments easy.
> 
> Reviewed-by: Kees Cook <kees@kernel.org>
> Reviewed-by: Jens Axboe <axboe@kernel.dk>
> Signed-off-by: Christian Brauner <brauner@kernel.org>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

> ---
>  include/linux/slab.h | 29 ++++++++++++++++++++++++++---
>  mm/slab_common.c     | 10 +++++-----
>  2 files changed, 31 insertions(+), 8 deletions(-)
> 
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index cb264dded324..f74ceb788ac1 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -261,9 +261,10 @@ struct kmem_cache *__kmem_cache_create_args(const char *name,
>  					    unsigned int object_size,
>  					    struct kmem_cache_args *args,
>  					    slab_flags_t flags);
> -struct kmem_cache *kmem_cache_create(const char *name, unsigned int size,
> -			unsigned int align, slab_flags_t flags,
> -			void (*ctor)(void *));
> +
> +struct kmem_cache *__kmem_cache_create(const char *name, unsigned int size,
> +				       unsigned int align, slab_flags_t flags,
> +				       void (*ctor)(void *));
>  struct kmem_cache *kmem_cache_create_usercopy(const char *name,
>  			unsigned int size, unsigned int align,
>  			slab_flags_t flags,
> @@ -272,6 +273,28 @@ struct kmem_cache *kmem_cache_create_usercopy(const char *name,
>  struct kmem_cache *kmem_cache_create_rcu(const char *name, unsigned int size,
>  					 unsigned int freeptr_offset,
>  					 slab_flags_t flags);
> +
> +/* If NULL is passed for @args, use this variant with default arguments. */
> +static inline struct kmem_cache *
> +__kmem_cache_default_args(const char *name, unsigned int size,
> +			  struct kmem_cache_args *args,
> +			  slab_flags_t flags)
> +{
> +	struct kmem_cache_args kmem_default_args = {};
> +
> +	/* Make sure we don't get passed garbage. */
> +	if (WARN_ON_ONCE(args))
> +		return NULL;
> +
> +	return __kmem_cache_create_args(name, size, &kmem_default_args, flags);
> +}
> +
> +#define kmem_cache_create(__name, __object_size, __args, ...)           \
> +	_Generic((__args),                                              \
> +		struct kmem_cache_args *: __kmem_cache_create_args,	\
> +		void *: __kmem_cache_default_args,			\
> +		default: __kmem_cache_create)(__name, __object_size, __args, __VA_ARGS__)
> +
>  void kmem_cache_destroy(struct kmem_cache *s);
>  int kmem_cache_shrink(struct kmem_cache *s);
>  
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 19ae3dd6e36f..418459927670 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -383,7 +383,7 @@ kmem_cache_create_usercopy(const char *name, unsigned int size,
>  EXPORT_SYMBOL(kmem_cache_create_usercopy);
>  
>  /**
> - * kmem_cache_create - Create a cache.
> + * __kmem_cache_create - Create a cache.
>   * @name: A string which is used in /proc/slabinfo to identify this cache.
>   * @size: The size of objects to be created in this cache.
>   * @align: The required alignment for the objects.
> @@ -407,9 +407,9 @@ EXPORT_SYMBOL(kmem_cache_create_usercopy);
>   *
>   * Return: a pointer to the cache on success, NULL on failure.
>   */
> -struct kmem_cache *
> -kmem_cache_create(const char *name, unsigned int size, unsigned int align,
> -		slab_flags_t flags, void (*ctor)(void *))
> +struct kmem_cache *__kmem_cache_create(const char *name, unsigned int size,
> +				       unsigned int align, slab_flags_t flags,
> +				       void (*ctor)(void *))
>  {
>  	struct kmem_cache_args kmem_args = {
>  		.align	= align,
> @@ -418,7 +418,7 @@ kmem_cache_create(const char *name, unsigned int size, unsigned int align,
>  
>  	return __kmem_cache_create_args(name, size, &kmem_args, flags);
>  }
> -EXPORT_SYMBOL(kmem_cache_create);
> +EXPORT_SYMBOL(__kmem_cache_create);
>  
>  /**
>   * kmem_cache_create_rcu - Create a SLAB_TYPESAFE_BY_RCU cache.
> 
> -- 
> 2.45.2
> 

-- 
Sincerely yours,
Mike.