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

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Date:	Thu, 13 Feb 2014 11:20:42 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	David Howells <dhowells@...hat.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	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 10:56 AM, Miklos Szeredi <miklos@...redi.hu> wrote:
>
> Fair enough, that allows the thing to be listed, at least.
>
> What about creation?  A new syscall?
>
> Removal?  unlink(2)?
>
> Should stat(2) succeed with a new filetype?

I think it had better work exactly like a special node (eg character
device etc). I don't know about creation (yes, we might even fake it
with mknod(), or just say that the only way to create them is as part
of the union-fs), but removal and renaming should absolutely *not* be
a new system call. That would be a disaster for any system admin,
having to use special tools to edit the filesystem.

Obviously when it is part of a union mount, whiteouts work differently
- they must *not* show up in getdents, and you can't rename/remove a
whiteout anywhere else. But that is obviously part of the union-fs,
nor the low-level filesystem itself.

            Linus
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