linux-kernel - Re: [PATCH 1/2] mm:zpool: constify struct zpool type

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Date:	Sat, 12 Sep 2015 09:29:21 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Seth Jennings <sjennings@...iantweb.net>,
	Dan Streetman <ddstreet@...e.org>,
	Minchan Kim <minchan@...nel.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCH 1/2] mm:zpool: constify struct zpool type

On (09/11/15 15:21), Andrew Morton wrote:
> > From: Sergey SENOZHATSKY <sergey.senozhatsky@...il.com>
> > 
> > Constify `struct zpool' ->type.
> > 
> 
> I think I prefer Dan's patch, which deletes stuff:

Sure, agree. Somehow I overlooked it.

	-ss


> From: Dan Streetman <ddstreet@...e.org>
> Subject: zpool: remove redundant zpool->type string, const-ify zpool_get_type
> 
> Make the return type of zpool_get_type const; the string belongs to the
> zpool driver and should not be modified.  Remove the redundant type field
> in the struct zpool; it is private to zpool.c and isn't needed since
> ->driver->type can be used directly.  Add comments indicating strings must
> be null-terminated.
> 
> Signed-off-by: Dan Streetman <ddstreet@...e.org>
> Cc: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
> Cc: Seth Jennings <sjennings@...iantweb.net>
> Cc: Minchan Kim <minchan@...nel.org>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> ---
> 
>  include/linux/zpool.h |    2 +-
>  mm/zpool.c            |   14 ++++++++------
>  2 files changed, 9 insertions(+), 7 deletions(-)
> 
> diff -puN include/linux/zpool.h~zpool-remove-redundant-zpool-type-string-const-ify-zpool_get_type include/linux/zpool.h
> --- a/include/linux/zpool.h~zpool-remove-redundant-zpool-type-string-const-ify-zpool_get_type
> +++ a/include/linux/zpool.h
> @@ -41,7 +41,7 @@ bool zpool_has_pool(char *type);
>  struct zpool *zpool_create_pool(char *type, char *name,
>  			gfp_t gfp, const struct zpool_ops *ops);
>  
> -char *zpool_get_type(struct zpool *pool);
> +const char *zpool_get_type(struct zpool *pool);
>  
>  void zpool_destroy_pool(struct zpool *pool);
>  
> diff -puN mm/zpool.c~zpool-remove-redundant-zpool-type-string-const-ify-zpool_get_type mm/zpool.c
> --- a/mm/zpool.c~zpool-remove-redundant-zpool-type-string-const-ify-zpool_get_type
> +++ a/mm/zpool.c
> @@ -18,8 +18,6 @@
>  #include <linux/zpool.h>
>  
>  struct zpool {
> -	char *type;
> -
>  	struct zpool_driver *driver;
>  	void *pool;
>  	const struct zpool_ops *ops;
> @@ -73,6 +71,7 @@ int zpool_unregister_driver(struct zpool
>  }
>  EXPORT_SYMBOL(zpool_unregister_driver);
>  
> +/* this assumes @type is null-terminated. */
>  static struct zpool_driver *zpool_get_driver(char *type)
>  {
>  	struct zpool_driver *driver;
> @@ -113,6 +112,8 @@ static void zpool_put_driver(struct zpoo
>   * not be loaded, and calling @zpool_create_pool() with the pool type will
>   * fail.
>   *
> + * The @type string must be null-terminated.
> + *
>   * Returns: true if @type pool is available, false if not
>   */
>  bool zpool_has_pool(char *type)
> @@ -145,6 +146,8 @@ EXPORT_SYMBOL(zpool_has_pool);
>   *
>   * Implementations must guarantee this to be thread-safe.
>   *
> + * The @type and @name strings must be null-terminated.
> + *
>   * Returns: New zpool on success, NULL on failure.
>   */
>  struct zpool *zpool_create_pool(char *type, char *name, gfp_t gfp,
> @@ -174,7 +177,6 @@ struct zpool *zpool_create_pool(char *ty
>  		return NULL;
>  	}
>  
> -	zpool->type = driver->type;
>  	zpool->driver = driver;
>  	zpool->pool = driver->create(name, gfp, ops, zpool);
>  	zpool->ops = ops;
> @@ -208,7 +210,7 @@ struct zpool *zpool_create_pool(char *ty
>   */
>  void zpool_destroy_pool(struct zpool *zpool)
>  {
> -	pr_debug("destroying pool type %s\n", zpool->type);
> +	pr_debug("destroying pool type %s\n", zpool->driver->type);
>  
>  	spin_lock(&pools_lock);
>  	list_del(&zpool->list);
> @@ -228,9 +230,9 @@ void zpool_destroy_pool(struct zpool *zp
>   *
>   * Returns: The type of zpool.
>   */
> -char *zpool_get_type(struct zpool *zpool)
> +const char *zpool_get_type(struct zpool *zpool)
>  {
> -	return zpool->type;
> +	return zpool->driver->type;
>  }
>  
>  /**
> _
> 
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