Date: Wed, 30 Mar 2005 13:06:01 -0700
From: Andreas Dilger <adilger@clusterfs.com>
To: David Malone <dwmalone@maths.tcd.ie>
Cc: linux-xfs@oss.sgi.com, linux-kernel@vger.kernel.org
Subject: Re: Directory link count wrapping on Linux/XFS/i386?
Message-ID: <20050330200601.GG1753@schnapps.adilger.int>
Mail-Followup-To: David Malone <dwmalone@maths.tcd.ie>,
	linux-xfs@oss.sgi.com, linux-kernel@vger.kernel.org
References: <200503302043.aa27223@salmon.maths.tcd.ie>
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On Mar 30, 2005  20:43 +0100, David Malone wrote:
> It seems that internally xfs uses a 32 bit field for the link count,
> and the stat64 syscalls use a 32 bit field. These fields are copied
> via the vattr structure in xfs_vnode.h, which uses a nlink_t for
> the link count. However, in the kernel, I think this field is
> actually of type __kernel_nlink_t which seems to be 16 bits on many
> platforms.
>=20
> I've tested this on an i386 2.6.11 kernel and it seems that the
> link count presented to userland wraps after 65536 subdirectories.
> This naturally doesn't let you screw up the filesystem or anything,
> but it does let you can hide files from find/fts, as demonstrated
> below.

The correct fix, used for reiserfs (and a patch for ext3 also) is to
set i_nlink =3D 1 in case the filesystem count has wrapped.  When nlink=3D=
=3D1
the fts/find code no longer optimizes subdirectory traversal and checks
each entries filetype to see if it should recurse.

Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.


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