Re: [PATCH v2 06/35] fs: super: introduce a get_super_cdev_thawed to get sb by cdev reference

From: Jan Kara <jack@suse.cz>
To: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
Cc: viro@ZenIV.linux.org.uk, jack@suse.cz, dedekind1@gmail.com,
	richard.weinberger@gmail.com, linux-mtd@lists.infradead.org,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v2 06/35] fs: super: introduce a get_super_cdev_thawed to get sb by cdev reference
Date: Mon, 3 Aug 2015 21:56:53 +0200	[thread overview]
Message-ID: <20150803195653.GD23810@quack.suse.cz> (raw)
In-Reply-To: <1438235311-23788-7-git-send-email-yangds.fnst@cn.fujitsu.com>

On Thu 30-07-15 13:48:02, Dongsheng Yang wrote:
> This patch refactors the original get_super_thawed to get a common
> helper function of __get_super_thawed. Then take the use of
> __get_super_thawed, we can implement get_super_cdev_thawed easily.
> 
> Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
> ---
>  fs/super.c         | 29 +++++++++++++++++++++++++----
>  include/linux/fs.h |  1 +
>  2 files changed, 26 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/super.c b/fs/super.c
> index 4c56dff..0e11412 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -629,18 +629,20 @@ struct super_block *get_super_cdev(struct cdev *cdev)
>  EXPORT_SYMBOL(get_super_cdev);
>  
>  /**
> - * get_super_thawed - get thawed superblock of a device
> - * @bdev: device to get the superblock for
> + * __get_super_thawed - get thawed superblock
> + * @func: function pointer to get superblock by key
> + * @key: key to find superblock
>   *
>   * Scans the superblock list and finds the superblock of the file system
>   * mounted on the device. The superblock is returned once it is thawed
>   * (or immediately if it was not frozen). %NULL is returned if no match
>   * is found.
>   */
> -struct super_block *get_super_thawed(struct block_device *bdev)
> +static struct super_block *__get_super_thawed(
> +		struct super_block *(*func)(void *), void *key)
>  {
>  	while (1) {
> -		struct super_block *s = get_super(bdev);
> +		struct super_block *s = func(key);

It would seem more obvious (and consistent with get_super() class of
functions) if you passed in a comparison function and a key and then call
from here:

s = __get_super(compare, key);

Also you would avoid some of the ugly typecasting below.

								Honza

>  		if (!s || s->s_writers.frozen == SB_UNFROZEN)
>  			return s;
>  		up_read(&s->s_umount);
> @@ -649,9 +651,28 @@ struct super_block *get_super_thawed(struct block_device *bdev)
>  		put_super(s);
>  	}
>  }
> +
> +/**
> + * get_super_thawed - get thawed superblock of a device
> + * @bdev: device to get the superblock for
> + */
> +struct super_block *get_super_thawed(struct block_device *bdev)
> +{
> +	return __get_super_thawed((struct super_block *(*)(void *))get_super, bdev);
> +}
>  EXPORT_SYMBOL(get_super_thawed);
>  
>  /**
> + * get_super_cdev_thawed - get thawed superblock of a char device
> + * @cdev: device to get the superblock for
> + */
> +struct super_block *get_super_cdev_thawed(struct cdev *cdev)
> +{
> +	return __get_super_thawed((struct super_block *(*)(void *))get_super_cdev, cdev);
> +}
> +EXPORT_SYMBOL(get_super_cdev_thawed);
> +
> +/**
>   * get_active_super - get an active reference to the superblock of a device
>   * @bdev: device to get the superblock for
>   *
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index e5ea425a..5c7d789 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2746,6 +2746,7 @@ extern struct file_system_type *get_fs_type(const char *name);
>  extern struct super_block *get_super(struct block_device *);
>  extern struct super_block *get_super_cdev(struct cdev *);
>  extern struct super_block *get_super_thawed(struct block_device *);
> +extern struct super_block *get_super_cdev_thawed(struct cdev *);
>  extern struct super_block *get_active_super(struct block_device *bdev);
>  extern void drop_super(struct super_block *sb);
>  extern void iterate_supers(void (*)(struct super_block *, void *), void *);
> -- 
> 1.8.4.2
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR