Re: Debugging corrupt object generation

From: Shawn O. Pearce <spearce@spearce.org>
Date: Nov 2, 2007, 05:15 UTC
Message-ID: <20071102051555.GB14735@spearce.org>
In-Reply-To: <Pine.LNX.4.64.0711020018400.18429@beast.quantumfyre.co.uk>

Julian Phillips <julian@quantumfyre.co.uk> wrote:

Show 10 quoted lines

> On Thu, 1 Nov 2007, Nicolas Pitre wrote:
> >
> >Maybe fast-import hasn't flushed the needed data to the pack yet?
> 
> Well, fast-import completes quite happily and outputs the normal summary 
> status.  I can look at logs and trees etc provided that I don't try and 
> look at one particular part of the tree on one particular commit.  I 
> think the problem is that I've managed to do something inside fast-import 
> that corrupts one particular tree object (though I've no idea what that 
> might be).

Ahhh. I'm betting you messed up the version 0 and version 1 arrays inside of the struct tree_entry. This could cause the delta generator to look at the wrong base information when it creates the delta, thus causing the delta to be created for a different base than what the object is actually using in the packfile.

The version[0] is meant to hold the mode and SHA-1 of the tree_entry in the base object. The version[1] is meant to hold the current mode and SHA-1 of the tree_entry in the new object. A mode of 0 means the entry doesn't exist in that particular tree; so an add is shown as "version[0].mode = 0; version[1].mode = 0100644".

Look at the store_tree function, this is where we regenerate the canonical representation of both the version[0] and the version[1] trees so the store_object function can generate a delta. Note that we assume the base object name is root->versions[0].sha1. Maybe the version[0] array doesn't actually match the tree named by that sha1?

-- 
Shawn.