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Re: [Help-tar] [PATCH] Add --clamp-mtime option


From: Jakob Bohm
Subject: Re: [Help-tar] [PATCH] Add --clamp-mtime option
Date: Thu, 04 Jun 2015 17:27:40 +0200
User-agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0

On 04/06/2015 16:48, Paul Eggert wrote:
An option along these lines sounds like it would be useful, thanks.  But I have some confusions and/or problems with the suggestion.

First, the patch doesn't alter the documentation, which is typically the hardest part of any change like this.  The documentation should give an example of how the new option would be useful.

Second, I'm having trouble seeing how to use the option (and this is probably because of the first item...).  How does the maintainer keep track of a clamped mtime?  Isn't that a hassle to maintain?  Can't 'tar' do this for you, instead of your having to do it?

Regarding the second issue: I believe the typical use would be to pass in a main packaging date (such as the date of /debian/changelog or the date of the top entry in that file), then any files newer than that (recompiled files) would get the fixed timestamp, while older files (such as manpages and default conffiles copied from the source tree) would keep their older timestamps, which might be the same over several package versions, thus reducing the size of binary deltas between deb files and improving the quality of conffile handling.

tar of cause has no memory, and should not have.  It is a tool that relies totally on its explicit inputs to produce the same output from the same input.  Anyway, tar would have very little chance to remember results across different buildds picking up the same source package.

Enjoy

Jakob
-- 
Jakob Bohm, CIO, Partner, WiseMo A/S.  https://www.wisemo.com
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