linux-kernel - Re: Nasty git corruption problem

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Message-ID: <Pine.LNX.4.63.0607272309460.29667@wbgn013.biozentrum.uni-wuerzburg.de>
Date:	Thu, 27 Jul 2006 23:11:49 +0200 (CEST)
From:	Johannes Schindelin <Johannes.Schindelin@....de>
To:	Linus Torvalds <torvalds@...l.org>
cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, linux-kernel@...r.kernel.org
Subject: Re: Nasty git corruption problem

Hi,

On Thu, 27 Jul 2006, Linus Torvalds wrote:

> 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...
> 
> 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.

Okay, I see your point.

> 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".

Why not just the good ole' locking mechanism? Update not the HEAD 
directly, but a HEAD.lock, and if all went well, rename it into HEAD (of 
course, by HEAD I mean refs/heads/<whatever-head-you-mean>).

Ciao,
Dscho

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