Re: RFC: adding xdelta compression to git

["C. Scott Ananian" <cscott@cscott.net>]

On Mon, 2 May 2005, Davide Libenzi wrote:

> On Mon, 2 May 2005, Linus Torvalds wrote:
>
>> Yes. EXCEPT for one thing. fsck. I'd _really_ like fsck to be able to know
>> something about any xdelta objects, if only because if/when things go

> Linus, xdelta-based algorithms already stores informations regarding the
> object that originated the diff. Since they have no context (like
> text-based diffs) and are simply based on offset-driven copy/insert
> operations, this is a requirement. Libxdiff uses an adler32+size of the
> original object, but you can get as fancy as you like in your own
> implementation. Before a delta patching, the stored information are cross
> checked with the input base object, and the delta patch will fail in the
> eventuality of mismatch. So an fsck is simply a walk backward (or forward,
> depending on your metadata model) of the whole delta chain.

Linus knows this.  His point is just to be sure you actually *code* that 
walk in fsck, and (hopefully) do so w/o complicating the fsck too much.
  --scott

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