Re: Understanding pack format

From: Jeff King <peff@peff.net>
Date: Nov 6, 2018, 06:09 UTC
Message-ID: <20181106060919.GA17521@sigill.intra.peff.net>
In-Reply-To: <CAFd4kYDcX2BOYvMg1X9zO68EfYYE6Zke_-9CGY-Yi01jCc3EPA@mail.gmail.com>

On Mon, Nov 05, 2018 at 09:23:45PM -0500, Farhan Khan wrote:

Show 9 quoted lines

> I am trying to identify where the content from a pack comes from. I
> traced it back to sha1-file.c:read_object(), which will return the
> 'content'. I want to know where the 'content' comes from, which seems
> to come from sha1-file.c:oid_object_info_extended. This goes into
> packfile.c:find_pack_entry(), but from here I get lost. I do not
> understand what is happening.
> 
> How does it retrieve the pack content? I am lost here. Please assist.
> This is in the technical git documentation, but it was not clear.

After find_pack_entry() tells us the object is in a pack, we end up in packed_object_info(). Depending what the caller is asking for, there are a couple different strategies (because we try to avoid loading the whole object if we don't need it).

Probably the one you're interested in is just grabbing the content, which happens via cache_or_unpack_entry(). The cached case is less interesting, so try unpack_entry(), which is what actually reads the bytes out of the packfile.

-Peff