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Re: [Bug-tar] Skipped files with --listed-incremental after rename

From: Paul Eggert
Subject: Re: [Bug-tar] Skipped files with --listed-incremental after rename
Date: 13 Oct 2003 15:15:58 -0700
User-agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.3

Joerg Schilling <address@hidden> writes:

> If a filesystem does not update st_ctime, then you cannot do simple meta data
> based incremental backups.

I tend to agree: it would have to get more complicated.  I don't see
any easy way out.

> If a filesystem does not update st_ctime, it breaks UNIX rules,
> since st_ctime indicates an inode change which I believe a rename(2)
> definitely is.

POSIX clearly allows a 'rename' implementation that does not update
ctime (there are some comments about this in the APPLICATION USAGE
section of the POSIX spec). Hence this will be a problem when any
simple metadata-based incremental backup scheme is run on any
filesystem implementation that takes advantage of this part of the
POSIX specification.

>From a filesystem implementer's viewpoint, I can see why they'd want
to avoid updating ctime: it can avoid writes to the disk in some cases.

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