linux-kernel - Re: [PATCH 1/3] ext4: Add alignment check for DAX mount

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Date:	Sun, 1 May 2016 10:31:15 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	Toshi Kani <toshi.kani@....com>
Cc:	dan.j.williams@...el.com, david@...morbit.com, jack@...e.cz,
	tytso@....edu, adilger.kernel@...ger.ca,
	ross.zwisler@...ux.intel.com, linux-nvdimm@...1.01.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] ext4: Add alignment check for DAX mount

On Fri, Apr 29, 2016 at 02:39:33PM -0600, Toshi Kani wrote:
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 304c712..90a8670 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -3421,6 +3421,12 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
>  					"error: unsupported blocksize for dax");
>  			goto failed_mount;
>  		}
> +		if (sb->s_bdev->bd_part->start_sect % (PAGE_SIZE / 512) ||
> +		    sb->s_bdev->bd_part->nr_sects % (PAGE_SIZE / 512)) {
> +			ext4_msg(sb, KERN_ERR,
> +					"error: unaligned partition for dax");
> +			goto failed_mount;
> +		}
>  		if (!sb->s_bdev->bd_disk->fops->direct_access) {
>  			ext4_msg(sb, KERN_ERR,
>  					"error: device does not support dax");

Factor your new checks and the ->direct_access into a new helper. It
should take the block device as file systems might have multiple
underlying devices.