Debian Bug report logs - #836211
dpkg: Cannot upgrade some packages on overlayfs: Invalid cross-device link

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Package: linux; Maintainer for linux is Debian Kernel Team <[email protected]>;

Affects: dpkg

Reported by: Felipe Sateler <[email protected]>

Date: Wed, 31 Aug 2016 15:18:06 UTC

Severity: normal

Tags: upstream

Found in versions 4.12.6-1, 4.6.4-1

Forwarded to [email protected]

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Date: Fri, 2 Sep 2016 15:03:54 +0200
From: Guillem Jover <[email protected]>
To: Miklos Szeredi <[email protected]>, [email protected]
Cc: Raphael Hertzog <[email protected]>,
	Felipe Sateler <[email protected]>,
	"[email protected]" <[email protected]>
Subject: Re: Bug#836211: dpkg: Cannot upgrade some packages on overlayfs:
 Invalid cross-device link
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	Miklos Szeredi <[email protected]>, [email protected],
	Raphael Hertzog <[email protected]>,
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User-Agent: NeoMutt/ (1.7.0)

Hi!

On Fri, 2016-09-02 at 14:30:58 +0200, Miklos Szeredi wrote:
> You are the first to report that this quirk actually causes problems
> in real life.
> 
> I have plans to fix this by adding a "redirector" attribute so that
> copied up directories (and perhaps files) can refer to lower directory
> that is found at a different ___location relative to the root of the
> overlay from the ___location of the upper directory.
> 
> Maybe an example can make this more clear:
> 
> lower/foo/bar/baz
> upper/foo/bar <- whiteout
> upper/moved/here <- redirects to "foo/bar"
> 
> will result in the tree:
> 
> overlay/moved/here/baz

That'd be very much appreciated, thanks!

> > It does not seem very correct to put the burden on user-space to be aware
> > of overlayfs restrictions such as this one. Renaming a directory is
> > not something that happens often in practice in the uses cases where
> > we use overlayfs but it's still frequent enough to deserve better than
> > a EXDEV error IMO and dpkg trying to rename "foo/" into "foo.dpkg-tmp/"
> > is in its right to assume that this rename will not cross any device
> > boundary.
> 
> The EXDEV trick  just works for mv(1), hence this didn't seem to be a
> big issue in practice.

In dpkg, the directory is rename(2)d to perform an atomic temporary backup,
so that it can be rolled-back in case of errors during unpacking. Having to
possibly do a deep-copy and a deep-remove, and then trying to recover from
errors inbetween those, would be very unsatisfactory.

Thanks,
Guillem

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