Re: Understanding pack format

From: Farhan Khan <khanzf@gmail.com>
Date: Nov 6, 2018, 02:23 UTC
Message-ID: <CAFd4kYDcX2BOYvMg1X9zO68EfYYE6Zke_-9CGY-Yi01jCc3EPA@mail.gmail.com>
In-Reply-To: <CACsJy8DFUeEddSa2z4VTSqhaUBJ4+SUf8xvjh6iWY2Phhh96iQ@mail.gmail.com>

On Fri, Nov 2, 2018 at 12:00 PM Duy Nguyen <pclouds@gmail.com> wrote:

Show 21 quoted lines

>
> On Fri, Nov 2, 2018 at 7:19 AM Junio C Hamano <gitster@pobox.com> wrote:
> >
> > Farhan Khan <khanzf@gmail.com> writes:
> >
> > > ...Where is this in the git code? That might
> > > serve as a good guide.
> >
> > There are two major codepaths.  One is used at runtime, giving us
> > random access into the packfile with the help with .idx file.  The
> > other is used when receiving a new packstream to create an .idx
> > file.
>
> The third path is copying/reusing objects in
> builtin/pack-objects.c::write_reuse_object(). Since it's mostly
> encoding the header of new objects in pack, it could also be a good
> starting point. Then you can move to write_no_reuse_object() and get
> how the data is encoded, deltified or not (yeah not parsed, but I
> think it's more or less the same thing conceptually).
> --
> Duy

Hi all,

To follow-up from the other day, I have been reading the code that retrieves the pack entry for the past 3 days now without much success. But there are quite a few abstractions and I get lost half-way down the line.

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.

Thank you,

-- Farhan Khan PGP Fingerprint: B28D 2726 E2BC A97E 3854 5ABE 9A9F 00BC D525 16EE