linux-kernel - Re: Nasty git corruption problem

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Message-ID: <Pine.LNX.4.64.0607271354270.4168@g5.osdl.org>
Date:	Thu, 27 Jul 2006 14:01:39 -0700 (PDT)
From:	Linus Torvalds <torvalds@...l.org>
To:	Johannes Schindelin <Johannes.Schindelin@....de>
cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, linux-kernel@...r.kernel.org
Subject: Re: Nasty git corruption problem

On Thu, 27 Jul 2006, Johannes Schindelin wrote:
> 
> On Thu, 27 Jul 2006, Linus Torvalds wrote:
> 
> > On Thu, 27 Jul 2006, Alan Cox wrote:
> > > 
> > > git-lost-found turns up some of the missing stuff that was applied
> > > earliest in the rebase but the other stuff is apparently neither visible
> > > anywhere in the tree or missing (the tree I was rebasing "^^^..." never
> > > shows it nor does the log).
> > 
> > Did you try "git-fsck-objects --full"?
> > 
> > The git-lost-found script is apparently broken, exactly because it doesn't 
> > do a "full".
> 
> Of course, I was assuming that nothing like repacking or pruning took 
> place after the crash...

That's not the point.

If somebody does a "git rebase", he might be changing the heads that have 
already been packed, and replacing them them with heads that have _not_ 
yet been packed. So the _dangling_ links are the old ones (in the 
pack-file), and "git-fsck-objects --full" is needed to see them.

That said, I still don't think Alan sees what he says he sees. Even if 
something crashes in the middle of a "git rebase", I think the old head 
should have been saved in .git/ORIG_HEAD, for example. 

That said, some of the more invasive operations (and "git rebase" 
certainly counts) should probably have a few "sync" operations to make 
sure that things like ORIG_HEAD really are on disk, so that we would be 
able to recreate the tree even _without_ anything like "git-fsck-objects".

		Linus
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