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Date: Fri, 17 Jan 2014 16:26:55 -0500
From: "J. Bruce Fields" <bfields@fieldses.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-nfs@vger.kernel.org,
        Miklos Szeredi <mszeredi@suse.cz>
Subject: Re: [PATCH] dcache: fix d_splice_alias handling of aliases
Message-ID: <20140117212655.GE26636@fieldses.org>
References: <20140115151749.GF23999@fieldses.org>
 <20140117121723.GA18375@infradead.org>
 <20140117153917.GA26636@fieldses.org>
 <20140117210343.GD26636@fieldses.org>
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On Fri, Jan 17, 2014 at 04:03:43PM -0500, J. Bruce Fields wrote:
> 	- d_splice_alias handles inode == NULL in the same way,

Actually, not exactly; simplifying a bit, in the NULL case they do:

	d_splice_alias:

		__d_instantiate(dentry, NULL);
		security_d_instantiate(dentry, NULL);
		if (d_unhashed(dentry))
			d_rehash(dentry);

	d_materialise_unique:

		BUG_ON(!d_unhashed(dentry));

		 __d_instantiate(dentry, NULL);
		 d_rehash(dentry);
		 security_d_instantiate(dentry, NULL);

and a comment on d_splice_alias says

	Cluster filesystems may call this function with a negative,
	hashed dentry.  In that case, we know that the inode will be a
	regular file, and also this will only occur during atomic_open.

I don't understand those callers.  But I guess it would be easy enough
to handle in d_materialise_unique.

--b.