Re: [PATCH 4/8] git-repack --max-pack-size: add fixup_header_footer()

On Mon, 9 Apr 2007, Shawn O. Pearce wrote:

Nicolas Pitre [off-list ref] wrote:

quoted

I think another file with common pack writing functions could be 
created.  Pack index writing is another item that is currently 
duplicated in pack-objects and index-pack for example.

I agree entirely.  And I'd like to see that refactoring occur
before this series, or as part of it.  At least for the nr_objects
correction routine.

That's easy enough for the nr_objects correction case.

The next obvious candidate would be index generation, but I'd wait a bit 
for all features in progress to be merged and stabilize first.

For example, writing objects to a packfile: we have 3
implementations.  fast-import.c doesn't use sha1write_compressed
because that was a waste of time to compute the SHA_CTX when we
know we have to go back and fixup nr_objects.  It also doesn't use
it because fast-import.c's pack-splitting logic is based on the
final object size, not the starting offset.  It does the deflate
itself, decides if the end of the object will overflow, and if so,
jumps to a new packfile.

I'd be really tempted to create a pack v4 which only change is to still 
have the pack header at the beginning of the pack like we do today, but 
include the header in the pack SHA1 computation at the end of the stream 
only.  This way the pack SHA1 could be computed as the pack is 
generated, and the header fixed up without having to read the entire 
pack back.  I think it was Geert Bosch who proposed this and it makes 
tons of sense IMHO.


Nicolas