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

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Date:	Thu, 13 Feb 2014 11:32:31 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	David Howells <dhowells@...hat.com>
Cc:	Miklos Szeredi <miklos@...redi.hu>,
	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 11:02 AM, David Howells <dhowells@...hat.com> wrote:
>
> Whilst that does seem reasonable, what about all the other software that
> iterates over a directory?  Some of that is surely not going to know about
> DT_WHT.

So?

Remeber: whiteout entries do not exist "normally". No normal apps
should care or see them, since the whole and only point of them is
when they are part of a union mount (in which case they are not
visible).

So the "how do you see whiteouts" is really only about the raw
filesystem mount when *not* in the normal place.

IOW, it's not like these guys are going to show up in users home
directories etc. It's more like a special device node than a file - we
need to care about some basic system management interfaces, not about
"random apps". So "coreutils" is the primary user, although I guess a
few IT people would prefer for things like Nautilus etc random file
managers to be able to show them nicely too. But if they show up as an
icon with a question mark on them or whatever, that's really not a big
deal either.

Sure, maybe they'll look odd in some graphical file chooser *if*
somebody makes them show up, but I think creation of a whiteout - if
we allow it at all outside of the union mount itself - should be a
root-only thing (the same way mknod is) so quite frankly, it falls
under "filesystem corruption makes my directory listings look odd -
cry me a river".

(I do think we should allow creation - but for root only - for
management and testing purposes, but I really think it's a secondary
issue, and I do think we should literally use "mknod()" - either with
a new S_IFWHT or even just making use of existing S_IFCHR just so you
could use the user-space "mknod" to create it with some magic
major/minor combination.

               Linus
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