From: Ben Peart <peartben@gmail.com>
Date: Tue, 02 Oct 2018 14:34:07 GMT
Subject: Re: [PATCH v7 3/7] eoie: add End of Index Entry (EOIE) extension
Message-ID: <dd8622f1-9005-a989-6934-2b9cd24c87a9@gmail.com>
In-Reply-To: <20181001151716.GL23446@localhost>



On 10/1/2018 11:17 AM, SZEDER Gábor wrote:
> On Mon, Oct 01, 2018 at 09:45:52AM -0400, Ben Peart wrote:
>> From: Ben Peart <benpeart@microsoft.com>
>>
>> The End of Index Entry (EOIE) is used to locate the end of the variable
>> length index entries and the beginning of the extensions. Code can take
>> advantage of this to quickly locate the index extensions without having
>> to parse through all of the index entries.
>>
>> Because it must be able to be loaded before the variable length cache
>> entries and other index extensions, this extension must be written last.
>> The signature for this extension is { 'E', 'O', 'I', 'E' }.
>>
>> The extension consists of:
>>
>> - 32-bit offset to the end of the index entries
>>
>> - 160-bit SHA-1 over the extension types and their sizes (but not
>> their contents).  E.g. if we have "TREE" extension that is N-bytes
>> long, "REUC" extension that is M-bytes long, followed by "EOIE",
>> then the hash would be:
>>
>> SHA-1("TREE" + <binary representation of N> +
>> 	"REUC" + <binary representation of M>)
>>
>> Signed-off-by: Ben Peart <peartben@gmail.com>
> 
> I think the commit message should explicitly mention that this this
> extension
> 
>    - will always be written and why,
>    - but is optional, so other Git implementations not supporting it will
>      have no troubles reading the index,
>    - and that it is written even to the shared index and why, and that
>      because of this the index checksums in t1700 had to be updated.
> 

Sure, I'll add that additional information to the commit message on the 
next spin.