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Date: Fri, 2 Mar 2018 23:53:16 +0100
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v5 02/12] dax: introduce IS_DEVDAX() and IS_FSDAX()
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To: Dan Williams <dan.j.williams@intel.com>
Cc: linux-nvdimm@lists.01.org, Theodore Ts'o <tytso@mit.edu>, Andreas Dilger <adilger.kernel@dilger.ca>, Alexander Viro <viro@zeniv.linux.org.uk>, "Darrick J. Wong" <darrick.wong@oracle.com>, linux-xfs@vger.kernel.org, Matthew Wilcox <mawilcox@microsoft.com>, Ross Zwisler <ross.zwisler@linux.intel.com>, stable@vger.kernel.org, Jan Kara <jack@suse.cz>, hch@lst.de, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org

> +static inline bool IS_DEVDAX(struct inode *inode)
> +{
> +	if (!IS_ENABLED(CONFIG_DEV_DAX))
> +		return false;
> +	if ((inode->i_flags & S_DAX) == 0)
> +		return false;
> +	if (!S_ISCHR(inode->i_mode))
> +		return false;
> +	return true;
> +}
> +
> +static inline bool IS_FSDAX(struct inode *inode)
> +{
> +	if (!IS_ENABLED(CONFIG_FS_DAX))
> +		return false;
> +	if ((inode->i_flags & S_DAX) == 0)
> +		return false;
> +	if (S_ISCHR(inode->i_mode))
> +		return false;
> +	return true;

Encoding the is char device or not thing here is just nasty.  I think
this is going entirely in the wrong direction.