ZERO LENGTH DIRECTORY & fsck

Robert Watson rwatson at freebsd.org
Wed Jul 28 07:40:45 PDT 2004


On Tue, 27 Jul 2004, Marc G. Fournier wrote:

> Is there anything that can be done to 'fix' this?  Under 4.x, using
> unionfs (and don't respond if your only answer is "its broken"), if it
> crashes, fsck finds a whack of the above ...

It's broken. :-)  But in all honesty, this has been discussed extensively,
and it's carefully documented in the man page.  So if you run into bugs,
it should not be a surprise.

> Now, I think I understand the *why* for the error ... union creates a
> 'mirror' of the file system, especially where a du/find is concerned,
> and teh ZLDs are 'end nodes' that have no files under them ... but is
> there a better way that fsck can handle those?  Its almost as if it
> doesn't know what to do with them, so has to remove them all ... 

Are you using union mounting of UFS or unionfs?  Theory tells us that
unionfs is a stacked file system layer, and shouldn't directly manipulate
the on-disk layout of UFS, instead, issuing vnode operations that allow
UFS to maintain its consistency guarantees.  Theory tells us that union
mounting UFS relies on UFS doing the magic, which means it has more
opportunity to currupt on disk storage.

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert at fledge.watson.org      Principal Research Scientist, McAfee Research




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