linux-kernel - Re: [PATCH 00/13] cross rename v4

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Date:	Thu, 13 Feb 2014 18:28:35 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	David Howells <dhowells@...hat.com>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Bruce Fields <bfields@...ldses.org>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Zach Brown <zab@...hat.com>, Jan Kara <jack@...e.cz>,
	Andy Lutomirski <luto@...capital.net>,
	"mszeredi@...e.cz" <mszeredi@...e.cz>
Subject: Re: [PATCH 00/13] cross rename v4

On Thu, Feb 13, 2014 at 5:42 PM, David Howells <dhowells@...hat.com> wrote:
> Miklos Szeredi <miklos@...redi.hu> wrote:
>
>> Regarding whiteouts, I raised a couple of questions that nobody answered
>> yet, so let me ask again.
>>
>> - If a filesystem containing whiteouts (fallthroughs, etc...) is mounted as
>>   not part of a union, how are these special entities represented to
>>   userspace?
>
> I would suggest that whiteouts appear as otherwise negative dentries and that
> they don't appear in getdents().

I'd argue that this is an administration nightmare.  E.g. what if the
a backup needs to be made of the rw layer?

Will rmdir work normally in a directory containing whiteouts?  Will
the VFS take care of that, just like if it was part of a union?  Or
will it fail with ENOTEMPTY despite *appearing* empty?

And zillion other problems related to the fact that things happen to a
filesystem even when they do not appear to happen ("mv foo bar; mv bar
foo" has side effects).

Thanks,
Miklos
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