Re: [PATCH v3 10/23] untracked cache: save to an index extension

> Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
> ---
> diff --git a/Documentation/technical/index-format.txt b/Documentation/technical/index-format.txt
> index fe6f316..b97ac8d 100644
> --- a/Documentation/technical/index-format.txt
> +++ b/Documentation/technical/index-format.txt
> @@ -233,3 +233,61 @@ Git index format
>    The remaining index entries after replaced ones will be added to the
>    final index. These added entries are also sorted by entry namme then
>    stage.
> +
> +== Untracked cache
> +
> +  Untracked cache saves the untracked file list and necessary data to
> +  verify the cache. The signature for this extension is { 'U', 'N',
> +  'T', 'R' }.
> +
> +  The extension starts with
> +
> +  - Stat data of $GIT_DIR/info/exclude. See "Index entry" section from
> +    ctime field until "file size".
> +
> +  - Stat data of core.excludesfile
> +
> +  - 32-bit dir_flags (see struct dir_struct)
> +
> +  - 160-bit SHA-1 of $GIT_DIR/info/exclude. Null SHA-1 means the file
> +    does not exist.
> +
> +  - 160-bit SHA-1 of core.excludesfile. Null SHA-1 means the file does
> +    not exist.
> +
> +  - NUL-terminated string of per-dir exclude file name. This usually
> +    is ".gitignore".
> +
> +  - The number of following directory blocks, variable width
> +    encoding. If this number is zero, the extension ends here with a
> +    following NUL.
> +
> +  - A number of directory blocks in depth-first-search order, each
> +    consists of
> +
> +    - The number of untracked entries, variable witdh encoding.

> +    - The directory name terminated by NUL.
> +
> +    - A number of untrached file/dir names terminated by NUL.
> +
> +The remaining data of each directory block is grouped by type:
> +
> +  - An ewah bitmap, the n-th bit marks whether the n-th directory has
> +    valid untracked cache entries.
> +
> +  - An ewah bitmap, the n-th bit records "check-only" bit of
> +    read_directory_recursive() for the n-th directory.
> +
> +  - An ewah bitmap, the n-th bit indicates whether SHA-1 and stat data
> +    is valid for the n-th directory and exists in the next data.
> +
> +  - An array of stat data. The n-th data corresponds with the n-th
> +    "one" bit in the previous ewah bitmap.
> +
> +  - An array of SHA-1. The n-th SHA-1 corresponds with the n-th "one" bit
> +    in the previous ewah bitmap.
> +
> +  - One NUL.