Re: [PATCH] cleancache: constify cleancache_ops structure

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Wed, Dec 23, 2015 at 10:06:24PM +0100, Julia Lawall wrote:
> The cleancache_ops structure is never modified, so declare it as const.
> 
> This also removes the __read_mostly declaration on the cleancache_ops
> variable declaration, since it seems redundant with const.
> 
> Done with the help of Coccinelle.
> 
> Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
> 
> ---
> 
> Not sure that the __read_mostly change is correct.  Does it apply to the
> variable, or to what the variable points to?

It should just put the structure in the right section (.rodata).

Thanks for the patch!
> 
>  drivers/xen/tmem.c         |    2 +-
>  include/linux/cleancache.h |    2 +-
>  mm/cleancache.c            |    4 ++--
>  3 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/cleancache.h b/include/linux/cleancache.h
> index bda5ec0b4..cb3e142 100644
> --- a/include/linux/cleancache.h
> +++ b/include/linux/cleancache.h
> @@ -37,7 +37,7 @@ struct cleancache_ops {
>  	void (*invalidate_fs)(int);
>  };
>  
> -extern int cleancache_register_ops(struct cleancache_ops *ops);
> +extern int cleancache_register_ops(const struct cleancache_ops *ops);
>  extern void __cleancache_init_fs(struct super_block *);
>  extern void __cleancache_init_shared_fs(struct super_block *);
>  extern int  __cleancache_get_page(struct page *);
> diff --git a/drivers/xen/tmem.c b/drivers/xen/tmem.c
> index 945fc43..4ac2ca8 100644
> --- a/drivers/xen/tmem.c
> +++ b/drivers/xen/tmem.c
> @@ -242,7 +242,7 @@ static int tmem_cleancache_init_shared_fs(char *uuid, size_t pagesize)
>  	return xen_tmem_new_pool(shared_uuid, TMEM_POOL_SHARED, pagesize);
>  }
>  
> -static struct cleancache_ops tmem_cleancache_ops = {
> +static const struct cleancache_ops tmem_cleancache_ops = {
>  	.put_page = tmem_cleancache_put_page,
>  	.get_page = tmem_cleancache_get_page,
>  	.invalidate_page = tmem_cleancache_flush_page,
> diff --git a/mm/cleancache.c b/mm/cleancache.c
> index 8fc5081..c6356d6 100644
> --- a/mm/cleancache.c
> +++ b/mm/cleancache.c
> @@ -22,7 +22,7 @@
>   * cleancache_ops is set by cleancache_register_ops to contain the pointers
>   * to the cleancache "backend" implementation functions.
>   */
> -static struct cleancache_ops *cleancache_ops __read_mostly;
> +static const struct cleancache_ops *cleancache_ops;
>  
>  /*
>   * Counters available via /sys/kernel/debug/cleancache (if debugfs is
> @@ -49,7 +49,7 @@ static void cleancache_register_ops_sb(struct super_block *sb, void *unused)
>  /*
>   * Register operations for cleancache. Returns 0 on success.
>   */
> -int cleancache_register_ops(struct cleancache_ops *ops)
> +int cleancache_register_ops(const struct cleancache_ops *ops)
>  {
>  	if (cmpxchg(&cleancache_ops, NULL, ops))
>  		return -EBUSY;
> 

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