threads / discuss / 9614

why git-reset needed after "cp -a" of a git repo?

Subject: why git-reset needed after "cp -a" of a git repo?

## tl;dr

5 messages between Aug 22, 2007 and Aug 22, 2007.

replies: 4people: 4as markdown or json

Erez Zadok· Aug 22, 2007, 18:57 UTC · lore

Apologies if this had been discussed before: I wasn't able to find this in the ML archives.

Sometimes I copy a whole git archive using cp -a, for experimental reasons, or otherwise; sometimes I rsync several git repos between remote and local computers to make access faster (it's often faster to rsync two git repos than to re-clone or deal with merge conflicts).

However, I noticed that after I copy a git repo (using v1.5.2.2), the index entries are all out of sync, and I need to run git-reset. Why? What's in the index file that changes after a cp -a or rsync that git depends on? Is it atime's and if so, aren't they copied by cp -a or rsync? If it depends on atime's, what happens if I mount my filesystem with noatime? Or does git's index depends on inode numbers which change after a cp -a? (BTW, I tried a variety of rsync options and none helped.) I also briefly looked at the source code and wasn't able to find the answer.

So, is there a way to efficiently copy a git repo on a local or remote host w/o having to rerun git-reset afterwards?

Thanks, Erez.

Jon Loeliger· Aug 22, 2007, 19:04 UTC · re: Erez Zadok · lore

Re: why git-reset needed after "cp -a" of a git repo?

On Wed, 2007-08-22 at 13:57, Erez Zadok wrote:
Show 11 quoted lines
> However, I noticed that after I copy a git repo (using v1.5.2.2), the index
> entries are all out of sync, and I need to run git-reset.  Why?  What's in
> the index file that changes after a cp -a or rsync that git depends on?  Is
> it atime's and if so, aren't they copied by cp -a or rsync?  If it depends
> on atime's, what happens if I mount my filesystem with noatime?  Or does
> git's index depends on inode numbers which change after a cp -a?  (BTW, I
> tried a variety of rsync options and none helped.)  I also briefly looked at
> the source code and wasn't able to find the answer.
> 
> So, is there a way to efficiently copy a git repo on a local or remote host
> w/o having to rerun git-reset afterwards?
Use "git update-index --refresh" to update time stamps in the index.
jdl
Linus Torvalds· Aug 22, 2007, 19:11 UTC · re: Erez Zadok · lore

Re: why git-reset needed after "cp -a" of a git repo?

On Wed, 22 Aug 2007, Erez Zadok wrote:
Show 5 quoted lines
> 
> However, I noticed that after I copy a git repo (using v1.5.2.2), the index
> entries are all out of sync, and I need to run git-reset.  Why?  What's in
> the index file that changes after a cp -a or rsync that git depends on?  Is
> it atime's and if so, aren't they copied by cp -a or rsync?
ctime/mtime and inode numbers too.

If you use hardlinks to copy the working tree, *and* you reset ctime afterwards, you'd be ok. But basically, git tries to be *really* anal in noticing any possible change to the inode, so anything it can do to notice that the index file might be stale, it does.

But you don't need to do a "git reset", you're actually better off just doing a "git status" instead. That will refresh the index.

		Linus
Erez Zadok· Aug 22, 2007, 19:19 UTC · re: Linus Torvalds · lore

Re: why git-reset needed after "cp -a" of a git repo?

In message <alpine.LFD.0.999.0708221208090.30176@woody.linux-foundation.org>, Linus Torvalds writes:
Show 20 quoted lines
> 
> 
> On Wed, 22 Aug 2007, Erez Zadok wrote:
> > 
> > However, I noticed that after I copy a git repo (using v1.5.2.2), the index
> > entries are all out of sync, and I need to run git-reset.  Why?  What's in
> > the index file that changes after a cp -a or rsync that git depends on?  Is
> > it atime's and if so, aren't they copied by cp -a or rsync?
> 
> ctime/mtime and inode numbers too.
> 
> If you use hardlinks to copy the working tree, *and* you reset ctime 
> afterwards, you'd be ok. But basically, git tries to be *really* anal in 
> noticing any possible change to the inode, so anything it can do to notice 
> that the index file might be stale, it does.
> 
> But you don't need to do a "git reset", you're actually better off just 
> doing a "git status" instead. That will refresh the index.
> 
> 		Linus

Thanks for the info and tips. It's a good idea of course to detect any possible changes, but I wonder if for those of us who know what they're doing (i.e., living on the edge :-), there could be an option to ignore inode numbers and just depend on good 'ol ctime/mtime (as other tools like make do).

If such an option might be deemed useful, I'm willing to take a crack at it.
Erez.
J. Bruce Fields· Aug 22, 2007, 20:14 UTC · re: Erez Zadok · lore

Re: why git-reset needed after "cp -a" of a git repo?

On Wed, Aug 22, 2007 at 03:19:23PM -0400, Erez Zadok wrote:
Show 5 quoted lines
> Thanks for the info and tips.  It's a good idea of course to detect any
> possible changes, but I wonder if for those of us who know what they're
> doing (i.e., living on the edge :-), there could be an option to ignore
> inode numbers and just depend on good 'ol ctime/mtime (as other tools like
> make do).

I don't think there's any need for that. You can always just run git-update-index --refresh or just git-status to refresh the stat data that's kept in the index. That miscellaneous stat data (ctime, mtime, inode number) is just there as an optimization, so git-diff doesn't have to read every file. It can be tossed out and regenerated any time.

--b.

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