[PATCH v8 3/6] mm/gup: Introduce memfd_pin_folios() for pinning memfd folios (v8)

[Matthew Wilcox]

On Fri, Dec 15, 2023 at 10:05:33PM -0800, Vivek Kasireddy wrote:
> +++ b/include/linux/memfd.h
> @@ -6,11 +6,16 @@
>  
>  #ifdef CONFIG_MEMFD_CREATE
>  extern long memfd_fcntl(struct file *file, unsigned int cmd, unsigned int arg);
> +extern struct folio *memfd_alloc_folio(struct file *memfd, pgoff_t idx);

You don't need the 'extern' for functions.

>  #else
>  static inline long memfd_fcntl(struct file *f, unsigned int c, unsigned int a)
>  {
>  	return -EINVAL;
>  }
> +static inline struct page *memfd_alloc_folio(struct file *memfd, pgoff_t idx)
> +{
> +	return ERR_PTR(-EINVAL);
> +}
>  #endif

Different return types depending on the CONFIG selected ...