Re: [PATCH 0/3] don't let disk corruptions escape pack SHA1 checksum

["Shawn O. Pearce" <spearce@xxxxxxxxxxx>]

Nicolas Pitre <nico@xxxxxxx> wrote:
> 
> So here is 3 patches for this in C git (Shawn already did it for jgit).
> 
> There are 3 spots where this needs to be plugged: in pack-objects, 
> index-pack and fast-import.  I did the first two.
> 
> I don't think this is that pertinent in fast-import because:
> 
>  - we want fast-import to be fast
> 
>  - after fast-import is done, a full repack is typically done which 
>    would revalidate everything (maybe fast-import should use index v2 
>    with its per object CRC32 though)
> 
> But maybe I'm wrong about that. In any case, I am leaving the 
> fast-import to someone more knowledgeable about its code than I do.

fast-import is the backend to a number of incremental import tools.
They stream data in from foreign VCS systems (notably Perforce)
and write into a live repository.  That repository may not get
repacked for days/weeks.  We should treat it just like index-pack.

So I think we should plug it.  The cost to keep a running SHA-1
for what we have written is pretty low.  I'd rather trade off a
minute or so on an hour long import for data safety than have a
chance for data corruption going unnoticed by the end user.

And now that index v2 is available, yea, fast-import should write
its index in that format so that a later repack can safely delta
reuse if it (by rare chance) decides the current packed form is the
best representation.  This is especially true with "git gc --auto"
triggering a repack every so often due to the incremental import
packs I just metioned above.

I've just been too busy with other things to add index v2 support.

-- 
Shawn.
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