Re: [PATCH v1 1/4] fastindex: speed up index load through parallelization

> How about I add the logic to write out a special extension right
> before the SHA1 that contains an offset to the beginning of the
> extensions section.  I will also add the logic in do_read_index() to
> search for and load this special extension if it exists.
>
> This will provide a common framework for any future extension to take
> advantage of if it wants to be loaded/processed before or in parallel
> with the cache entries or other extensions.
>
> For all existing extensions that assume they are loaded _after_ the
> cache entries, in do_read_index() I'll add the logic to use the offset
> (if it exists) to adjust the src_offset and then load them normally.
>
> Given the IEOT extension is just another list of offsets into the
> index to enable out of order processing, I'll add those offsets into
> the same extension so that it is a more generic "table of contents"
> for the entire index.  This enables us to have common/reusable way to
> have random access to _all_ sections in the index while maintaining
> backwards comparability with the existing index formats and code.
>
> These additional offsets will initially only be used to parallelize
> the loading of cache entries and only if the user explicitly enables
> that option but I can think of other interesting uses for them in the
> future.