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On Wed, 25 Nov 2009 14:13:58 -0700 |
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Denis Dupeyron <calchan@g.o> wrote: |
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> A quick note to tell you that I have tried to look for examples of |
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> breakage due to how mtime preservation is currently implemented in |
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> portage. Unfortunately I didn't find anything, maybe because I'm not |
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> knowledgeable enough or because I can't afford to spend any more time |
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> on this. If any of you can provide an example then please do so. |
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|
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Portage uses two ways of merging a file: os.rename() and the manual |
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way. |
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|
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os.rename() correctly preserves mtimes. |
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|
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Python's os.utime call, which is what Portage uses to preserve mtimes |
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for files that it installs the hard way, and which is not a wrapper for |
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the Unix utime call, uses an IEEE 754 double to handle timestamps. But |
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a double only gives sixteen accurate decimal digits, and you've got ten |
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to the left of the decimal point, leaving only six reliably preserved, |
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with the remaining three digits being corrupted. |
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|
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Thus, packages can end up being installed with some files having |
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accurately-preserved mtimes, and some having corrupted mtimes, which |
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will lead to mtime comparisons giving incorrect results. |
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|
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-- |
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Ciaran McCreesh |
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