From: Al Viro <viro@ZenIV.linux.org.uk>
To: George Spelvin <linux@horizon.com>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
miklos@szeredi.hu
Subject: Re: [PATCH 00/13] overlay filesystem: request for inclusion (v16)
Date: Wed, 20 Mar 2013 21:32:05 +0000 [thread overview]
Message-ID: <20130320213205.GR21522@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20130320194108.24192.qmail@science.horizon.com>
On Wed, Mar 20, 2013 at 03:41:08PM -0400, George Spelvin wrote:
> Sorry for being so very late to the party, but rather than messing
> with xattrs, why not just have a specific file (say, default /.whiteout,
> but selectable via a mount option) and links to it are counted as
> whiteout entries?
>
> All you need to do is resolve the link (it's probably a good idea
> to allow symlinks to avoid hard-link count limits) and compare the
> fs and inode number.
>
> It's kind of hackish, but it could be done on pretty much *any* Unix
> file system. VFAT would be SOL, but that's probably acceptable.
>
> (Any security options on mount point crossing or consistent ownership
> of symlinks that you want to impose would probably be of general VFS
> use, and again, not FS-specific.)
Yeah... Now, think what rm -rf foo/ would be doing. We read the
underlying directory. For each file in it we create a link to that
magical file of yours in covering one. _Then_ we do rmdir(), and what a joy
it turns out to be - we
* lock the covering directory
* read the covering directory and stat everything in it, checking that
it's a link to your file; we also read the underlying directory and verify
that everything in it has a matching whiteout in the covering one.
* once we are through, we read it *again*, this time doing unlinks
and praying real hard we won't crash in the meanwhile
* once that is finished, we finally can rmdir the fucker and unlock
its inode.
I'm sorry, but this is insane.
next prev parent reply other threads:[~2013-03-20 21:32 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-03-20 19:41 [PATCH 00/13] overlay filesystem: request for inclusion (v16) George Spelvin
2013-03-20 21:32 ` Al Viro [this message]
2013-03-22 5:15 ` Rob Landley
-- strict thread matches above, loose matches on Subject: below --
2013-03-12 15:41 Miklos Szeredi
2013-03-12 16:49 ` Sedat Dilek
2013-03-12 20:00 ` Miklos Szeredi
2013-03-12 17:22 ` J. R. Okajima
2013-03-12 20:01 ` Miklos Szeredi
2013-03-12 21:50 ` Linus Torvalds
2013-03-12 22:23 ` Al Viro
2013-03-13 9:42 ` Sedat Dilek
2013-03-13 15:24 ` Miklos Szeredi
2013-03-13 18:52 ` Al Viro
2013-03-13 22:09 ` Miklos Szeredi
2013-03-13 23:19 ` Al Viro
2013-03-14 10:37 ` Miklos Szeredi
2013-03-14 22:59 ` Al Viro
2013-03-18 11:27 ` Miklos Szeredi
2013-03-13 10:09 ` Sedat Dilek
2013-03-13 10:57 ` Miklos Szeredi
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