standarize mtime when git checkout

standarize mtime when git checkout

[Rick Liu]

Hi,

Currently when doing "git checkout" (either for a branch or a tag),
if the file doesn't exist before,
the file will be created using current datetime.

This causes problem while trying to tar the git repository source files (excluding .git folder).
The tar binary can be different 
even all of file contents are the same (eg. from the same GIT commit)
because the mtime for the files might be different due to different "git checkout" time.

eg:
User A checkout the commit at time A and then tarball the folder.
User B checkout the same commit as time B and then tarball the folder.
The result tarball are binary different 
even though all of tarball contents are the same 
except the mtime for each file.


Can we use GIT's commit time as the mtime for all of files/folders when we do "git checkout"?


Rick

Re: standarize mtime when git checkout

[Junio C Hamano]

"Rick Liu" <rickliu@broadcom.com> writes:

> Can we use GIT's commit time as the mtime for all of files/folders when we do "git checkout"?

No.  That will screw up common practice of build based on file
timestamps (e.g. make).

You may be interested in "git archive $commit" which will set the file
timestamps that of the commit object.

Re: standarize mtime when git checkout

[René Scharfe]

Am 08.07.2013 23:39, schrieb Rick Liu:
> Hi,
>
> Currently when doing "git checkout" (either for a branch or a tag),
> if the file doesn't exist before,
> the file will be created using current datetime.
>
> This causes problem while trying to tar the git repository source files (excluding .git folder).
> The tar binary can be different
> even all of file contents are the same (eg. from the same GIT commit)
> because the mtime for the files might be different due to different "git checkout" time.
>
> eg:
> User A checkout the commit at time A and then tarball the folder.
> User B checkout the same commit as time B and then tarball the folder.
> The result tarball are binary different
> even though all of tarball contents are the same
> except the mtime for each file.
>
>
> Can we use GIT's commit time as the mtime for all of files/folders when we do "git checkout"?

That would break tools like make which rely on a files mtime to build 
them.  They wouldn't be able to detect switching between source file 
versions that are older than the latest build.

You can use "git archive" to create tar files in which all entries have 
their mtime set to the commit time.  Such archives only contain tracked 
(committed) files, though.  And different versions of git can create 
slightly different archives, but such changes have been rare.

René

RE: standarize mtime when git checkout

[Rick Liu]

Thanks René~
I'll use "git archive" command to create the tarball.

Rick

-----Original Message-----
From: René Scharfe [mailto:rene.scharfe@lsrfire.ath.cx] 
Sent: Monday, July 08, 2013 8:54 PM
To: Rick Liu
Cc: git@vger.kernel.org
Subject: Re: standarize mtime when git checkout

Am 08.07.2013 23:39, schrieb Rick Liu:
> Hi,
>
> Currently when doing "git checkout" (either for a branch or a tag),
> if the file doesn't exist before,
> the file will be created using current datetime.
>
> This causes problem while trying to tar the git repository source files (excluding .git folder).
> The tar binary can be different
> even all of file contents are the same (eg. from the same GIT commit)
> because the mtime for the files might be different due to different "git checkout" time.
>
> eg:
> User A checkout the commit at time A and then tarball the folder.
> User B checkout the same commit as time B and then tarball the folder.
> The result tarball are binary different
> even though all of tarball contents are the same
> except the mtime for each file.
>
>
> Can we use GIT's commit time as the mtime for all of files/folders when we do "git checkout"?

That would break tools like make which rely on a files mtime to build 
them.  They wouldn't be able to detect switching between source file 
versions that are older than the latest build.

You can use "git archive" to create tar files in which all entries have 
their mtime set to the commit time.  Such archives only contain tracked 
(committed) files, though.  And different versions of git can create 
slightly different archives, but such changes have been rare.

René