Re: [gentoo-dev] mtime preservation

[Ciaran McCreesh <ciaran.mccreesh@googlemail.com>]

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On Wed, 25 Nov 2009 23:59:45 +0100
Ulrich Mueller <ulm@gentoo.org> wrote:
> Real examples would be issues like bugs 83877 [1] or 263387 [2].
> Nothing that could be easily dismissed or worked around. Both issues
> are fixed with Portage since a long time.

Yes, those are examples of packages relying upon something that is
undefined behaviour, and that behaves differently depending upon the
Portage version you use.

> I don't know of any example where non-preservation of nanosecond
> timestamps would cause problems.

Not non-preservation. Partial and inconsistent corruption.

srcfile gets installed with its mtime preserved, because it is installed
using rename.

objfile, whose mtime should be a bit later than srctime's, gets
installed with its mtime corrupted to be slightly less than it should
be, and less than srctime's, because it is installed the slow way.

A program checks that objfile's mtime is greater than or equal to
srcfile's mtime. That check will fail, and reinstalls will randomly fix
and break it depending upon which way the corruption goes.

-- 
Ciaran McCreesh

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