From: Derrick Stolee <stolee@gmail.com>
Date: Thu, 12 Apr 2018 11:28:11 GMT
Subject: Re: [PATCH v8 03/14] commit-graph: add format document
Message-ID: <c2f639ba-4832-191e-03ae-fa893796e2a6@gmail.com>
In-Reply-To: <86zi294fzq.fsf@gmail.com>

On 4/11/2018 4:58 PM, Jakub Narebski wrote:
> Derrick Stolee <stolee@gmail.com> writes:
>
>> +CHUNK DATA:
>> +
>> +  OID Fanout (ID: {'O', 'I', 'D', 'F'}) (256 * 4 bytes)
>> +      The ith entry, F[i], stores the number of OIDs with first
>> +      byte at most i. Thus F[255] stores the total
>> +      number of commits (N).
>> +
>> +  OID Lookup (ID: {'O', 'I', 'D', 'L'}) (N * H bytes)
>> +      The OIDs for all commits in the graph, sorted in ascending order.
>> +
>> +  Commit Data (ID: {'C', 'G', 'E', 'T' }) (N * (H + 16) bytes)
> I think it is a typo, and it should be CDAT, not CGET
> (CDAT seem to me to stand for Commit DATa):
>
>    +  Commit Data (ID: {'C', 'D', 'A', 'T' }) (N * (H + 16) bytes)
>
> This is what you use in actual implementation, in PATCH v8 06/14
>
> DS> +#define GRAPH_SIGNATURE 0x43475048 /* "CGPH" */
> DS> +#define GRAPH_CHUNKID_OIDFANOUT 0x4f494446 /* "OIDF" */
> DS> +#define GRAPH_CHUNKID_OIDLOOKUP 0x4f49444c /* "OIDL" */
> DS> +#define GRAPH_CHUNKID_DATA 0x43444154 /* "CDAT" */
> DS> +#define GRAPH_CHUNKID_LARGEEDGES 0x45444745 /* "EDGE" */
>

Documentation bugs are hard to diagnose. Thanks for finding this. I 
double checked that the hex int "0x43444154" matches "CDAT".

Here is a diff to make it match.

diff --git a/Documentation/technical/commit-graph-format.txt 
b/Documentation/technical/commit-graph-format.txt
index ad6af8105c..af03501834 100644
--- a/Documentation/technical/commit-graph-format.txt
+++ b/Documentation/technical/commit-graph-format.txt
@@ -70,7 +70,7 @@ CHUNK DATA:
    OID Lookup (ID: {'O', 'I', 'D', 'L'}) (N * H bytes)
        The OIDs for all commits in the graph, sorted in ascending order.

-  Commit Data (ID: {'C', 'G', 'E', 'T' }) (N * (H + 16) bytes)
+  Commit Data (ID: {'C', 'D', 'A', 'T' }) (N * (H + 16) bytes)
      * The first H bytes are for the OID of the root tree.
      * The next 8 bytes are for the positions of the first two parents
        of the ith commit. Stores value 0xffffffff if no parent in that