Re: [Bug-tar] [Fwd: Bug#556114: patch]

[Eric Blake]

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According to Bdale Garbee on 11/25/2009 7:22 AM:
> Issues not solved by this patch:
> - For filesystems with a better time resolution than 1 second, more
>   files may be included in incremental backups than strictly necessary,
>   but never more than 1 second worth. IMHO this is preferable to the
>   alternative of some files not being included on filesystems with a
>   larger time resolution. Especially since this is not limited to the
>   snapshot case, but can (will) also happen during regular dumps - see
>   above.

The gnulib module utimecmp helps deal with this.  However, gnulib has also
empirically determined that you need a window of at least 20 milliseconds,
even with utimensat and filesystems that support full nanosecond
resolution, since many OSs quantize timestamps to something like a 10
millisecond boundary even though you can access the additional resolution.
 But 20 milliseconds is indeed smaller than 1 second, when there is enough
support.

> - For filesystems with a worse time resolution than 1 second, files
>   may still be left out of an incremental backup. In that case, the
>   behavior is no worse than it is now.

The only file system in this category is FAT, and its resolution is 2
seconds.  But FAT has other problems, such as lack of permissions.

- --
Don't work too hard, make some time for fun as well!

Eric Blake             address@hidden
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