Re: [PATCH v5 2/4] ls-files: optionally recurse into submodules

> Allow ls-files to recognize submodules in order to retrieve a list of
> files from a repository's submodules.  This is done by forking off a
> process to recursively call ls-files on all submodules. Use top-level
> --super-prefix option to pass a path to the submodule which it can
> use to prepend to output or pathspec matching logic.
>
> Signed-off-by: Brandon Williams <bmwill@google.com>
> ---
>  Documentation/git-ls-files.txt         |   7 +-
>  builtin/ls-files.c                     | 139 ++++++++++++++++++++++++---------
>  git.c                                  |   2 +-
>  t/t3007-ls-files-recurse-submodules.sh | 100 ++++++++++++++++++++++++
>  4 files changed, 208 insertions(+), 40 deletions(-)
>  create mode 100755 t/t3007-ls-files-recurse-submodules.sh
>
> diff --git a/Documentation/git-ls-files.txt b/Documentation/git-ls-files.txt
> index 0d933ac..446209e 100644
> --- a/Documentation/git-ls-files.txt
> +++ b/Documentation/git-ls-files.txt
> @@ -18,7 +18,8 @@ SYNOPSIS
>                 [--exclude-per-directory=<file>]
>                 [--exclude-standard]
>                 [--error-unmatch] [--with-tree=<tree-ish>]
> -               [--full-name] [--abbrev] [--] [<file>...]
> +               [--full-name] [--recurse-submodules]
> +               [--abbrev] [--] [<file>...]
>
>  DESCRIPTION
>  -----------
> @@ -137,6 +138,10 @@ a space) at the start of each line:
>         option forces paths to be output relative to the project
>         top directory.
>
> +--recurse-submodules::
> +       Recursively calls ls-files on each submodule in the repository.
> +       Currently there is only support for the --cached mode.
> +
>  --abbrev[=<n>]::
>         Instead of showing the full 40-byte hexadecimal object
>         lines, show only a partial prefix.
> diff --git a/builtin/ls-files.c b/builtin/ls-files.c
> index 00ea91a..e0e5cf5 100644
> --- a/builtin/ls-files.c
> +++ b/builtin/ls-files.c
> @@ -14,6 +14,7 @@
>  #include "resolve-undo.h"
>  #include "string-list.h"
>  #include "pathspec.h"
> +#include "run-command.h"
>
>  static int abbrev;
>  static int show_deleted;
> @@ -28,8 +29,10 @@ static int show_valid_bit;
>  static int line_terminator = '\n';
>  static int debug_mode;
>  static int show_eol;
> +static int recurse_submodules;
>
>  static const char *prefix;
> +static const char *super_prefix;
>  static int max_prefix_len;
>  static int prefix_len;
>  static struct pathspec pathspec;
> @@ -68,6 +71,19 @@ static void write_eolinfo(const struct cache_entry *ce, const char *path)
>  static void write_name(const char *name)
>  {
>         /*
> +        * Prepend the super_prefix to name to construct the full_name to be
> +        * written.  'full_name' gets reused across output lines to minimize the
> +        * allocation churn.
> +        */