linux-ext4 - Re: [PATCH v3 2/3] dax: change bdev_dax_supported() to support boolean returns

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Date:   Tue, 13 Feb 2018 13:31:48 -0700
From:   Ross Zwisler <ross.zwisler@...ux.intel.com>
To:     Dave Jiang <dave.jiang@...el.com>
Cc:     darrick.wong@...cle.com, linux-nvdimm@...ts.01.org,
        david@...morbit.com, linux-xfs@...r.kernel.org,
        ross.zwisler@...ux.intel.com, linux-ext4@...r.kernel.org,
        dan.j.williams@...el.com
Subject: Re: [PATCH v3 2/3] dax: change bdev_dax_supported() to support
 boolean returns

On Thu, Feb 08, 2018 at 05:38:19PM -0700, Dave Jiang wrote:
> The function return values are confusing with the way the function is
> named. We expect a true or false return value but it actually returns
> 0/-errno.  This makes the code very confusing. Changing the return values
> to return a bool where if DAX is supported then return true and no DAX
> support returns false.
> 
> Signed-off-by: Dave Jiang <dave.jiang@...el.com>
> ---

> diff --git a/fs/ext2/super.c b/fs/ext2/super.c
> index 655699321c45..636b9c5e1bff 100644
> --- a/fs/ext2/super.c
> +++ b/fs/ext2/super.c
> @@ -958,9 +958,10 @@ static int ext2_fill_super(struct super_block *sb, void *data, int silent)
>  	blocksize = BLOCK_SIZE << le32_to_cpu(sbi->s_es->s_log_block_size);
>  
>  	if (sbi->s_mount_opt & EXT2_MOUNT_DAX) {
> -		err = sb_dax_supported(sb, blocksize);
> -		if (err)
> +		if(!sb_dax_supported(sb, blocksize)) {
> +			err = -EIO;

No need to set 'err' here.  This is just a temporary variable used for some
local checks later in the function.  'ret' is the value that will be returned,
and that is already initialized to -EINVAL which should be fine.

>  			goto failed_mount;
> +		}
>  	}
>  
>  	/* If the blocksize doesn't match, re-read the thing.. */
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 804a2d6729af..7b7650ac9c53 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -3712,9 +3712,10 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
>  					" that may contain inline data");
>  			goto failed_mount;
>  		}
> -		err = sb_dax_supported(sb, blocksize);
> -		if (err)
> +		if (!sb_dax_supported(sb, blocksize)) {
> +			err = -EIO;

Same comment as with the ext2 case - no need to set 'err', 'ret' is -EINVAL
and has you covered.