Re: My git repo is broken, how to fix it ?

From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Mar 22, 2007, 15:58 UTC
Message-ID: <Pine.LNX.4.64.0703220847540.6730@woody.linux-foundation.org>
In-Reply-To: <200703210956.50018.litvinov2004@gmail.com>

[ Sorry, I got sidetracked, have been looking at kernel bugs and git 
  optimizations. I added back the git mailing list, since there is no 
  private file data here any more, and I'd like others to follow this
  saga too ]

On Wed, 21 Mar 2007, Alexander Litvinov wrote:

Show 11 quoted lines

>
> > Oh, btw, before I do that - do you by any chance have the *uncorrupt*
> > version of the file that should be this object? In other words, do you
> > have object 03312463e194d68d0d677b51e09b47cb29ca926a in another
> > repository? It should be a version of your file.
>
> It is pity, but I don't have that version. It was broken at my last commit and 
> I will redo it again. I remeber the changes I have done.
> 
> The new file has different sha1 sum but I attach it to show you the real file 
> content.

Sadly, I actually would need to compare it to the exact object it *should* have generated, and that means that I'm not actually all that interested in the "real file content" per se, I really would need to see the exact blob, so that I can generate the object it should have been, and then compare that against the corrupt one...

It's the binary data I'd like to compare, so that I can tell (for example) if there is just a chunk missing in the middle, or something like that. But since even slight differences in the source data will lead to different binary data, and since the compressed and corrupt data I have from you earlier doesn't make sense on its own, I do care about the exact object that got corrupted.

Show 6 quoted lines

> By the way, I now I am using git (3ba7a10) taken from next with tree your 
> patches:
> 1. disables the hardlinking code for CYGWIN, and it also checks for errors 
> from "close()"
> 2. Don't ever return corrupt objects from "parse_object()"
> 3. Be more careful about zlib return values.

Ok, apart from #1, those should be in current -git now, along with better validation checks (by Nico) when packing. So hopefully at least when there is corruption in a loose object, we will now always notice when we do a "git repack", and will never generate a broken pack-file. Knock wood.

Of course, I actually wonder if the bug might be in your version of zlib (miscompiled or some other thing), in which case *any* amount of pre-validation won't really help, because it will become corrupted when we deflate it prior to writing. For example, if "deflateBound()" sometimes doesn't give a valid upper bound and we allocate too little space..

> Yesterday brakage was made by git with only first patch.

I see that you seem to be able to reproduce it again - I'll answer that email separately just so that the git list sees that message too. But it boils down to: if it's reproducible, I'd *really* like to see the corrupted object and the exact file that it should have been generated from..

		Linus