Re: [PATCH 2/3] ieot: default to not writing IEOT section

> As with EOIE, popular versions of Git do not support the new IEOT
> extension yet.  When accessing a Git repository written by a more
> modern version of Git, they correctly ignore the unrecognized section,
> but in the process they loudly warn
> 
> 	ignoring IEOT extension
> 
> resulting in confusion for users.  Introduce the index extension more
> gently by not writing it yet in this first version with support for
> it.  Soon, once sufficiently many users are running a modern version
> of Git, we can flip the default so users benefit from this index
> extension by default.
> 
> Introduce a '[index] recordOffsetTable' configuration variable to
> control whether the new index extension is written.
> 

> Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
> ---
>   Documentation/config.txt |  7 +++++++
>   read-cache.c             | 11 ++++++++++-
>   2 files changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/config.txt b/Documentation/config.txt
> index d702379db4..cc66fb7de3 100644
> --- a/Documentation/config.txt
> +++ b/Documentation/config.txt
> @@ -2195,6 +2195,13 @@ index.recordEndOfIndexEntries::
>   	reading the index using Git versions before 2.20. Defaults to
>   	'false'.
>   
> +index.recordOffsetTable::
> +	Specifies whether the index file should include an "Index Entry
> +	Offset Table" section. This reduces index load time on
> +	multiprocessor machines but produces a message "ignoring IEOT
> +	extension" when reading the index using Git versions before 2.20.
> +	Defaults to 'false'.
> +
>   index.threads::
>   	Specifies the number of threads to spawn when loading the index.
>   	This is meant to reduce index load time on multiprocessor machines.
> diff --git a/read-cache.c b/read-cache.c
> index 4bfe93c4c2..290bd54708 100644
> --- a/read-cache.c
> +++ b/read-cache.c
> @@ -2707,6 +2707,15 @@ static int record_eoie(void)
>   	return 0;
>   }
>   
> +static int record_ieot(void)
> +{
> +	int val;
> +
> +	if (!git_config_get_bool("index.recordoffsettable", &val))
> +		return val;
> +	return 0;
> +}
> +
>   /*
>    * On success, `tempfile` is closed. If it is the temporary file
>    * of a `struct lock_file`, we will therefore effectively perform
> @@ -2767,7 +2776,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
>   
>   #ifndef NO_PTHREADS
>   	nr_threads = git_config_get_index_threads();
> -	if (nr_threads != 1) {
> +	if (nr_threads != 1 && record_ieot()) {
>   		int ieot_blocks, cpus;
>   
>   		/*
>