Re: [PATCH v7 11/31] $GIT_COMMON_DIR: a new environment variable

> This variable is intended to support multiple working directories
> attached to a repository. Such a repository may have a main working
> directory, created by either "git init" or "git clone" and one or more
> linked working directories. These working directories and the main
> repository share the same repository directory.
>
> Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
> ---
> diff --git a/Documentation/gitrepository-layout.txt b/Documentation/gitrepository-layout.txt
> index 17d2ea6..7629e38 100644
> --- a/Documentation/gitrepository-layout.txt
> +++ b/Documentation/gitrepository-layout.txt
> @@ -133,6 +138,11 @@ being a symref to point at the current branch.  Such a state
>  is often called 'detached HEAD.'  See linkgit:git-checkout[1]
>  for details.
>
> +config::
> +       Repository specific configuration file. This file is ignored

> +       $GIT_COMMON_DIR is set and "$GIT_COMMON_DIR/config" will be
> +       used instead.
> +
>  branches::
>         A slightly deprecated way to store shorthands to be used
>         to specify a URL to 'git fetch', 'git pull' and 'git push'.
> diff --git a/environment.c b/environment.c
> index fee12a6..6b74f68 100644
> --- a/environment.c
> +++ b/environment.c
> @@ -149,9 +149,18 @@ static void setup_git_env(void)
>                 git_dir = DEFAULT_GIT_DIR_ENVIRONMENT;
>         gitfile = read_gitfile(git_dir);
>         git_dir = xstrdup(gitfile ? gitfile : git_dir);
> -       git_object_dir = git_path_from_env(DB_ENVIRONMENT, "objects", &git_db_env);
> -       git_index_file = git_path_from_env(INDEX_ENVIRONMENT, "index", &git_index_env);
> -       git_graft_file = git_path_from_env(GRAFT_ENVIRONMENT, "info/grafts", &git_graft_env);
> +       git_common_dir = getenv(GIT_COMMON_DIR_ENVIRONMENT);
> +       if (git_common_dir) {
> +               git_common_dir_env = 1;
> +               git_common_dir = xstrdup(git_common_dir);
> +       } else
> +               git_common_dir = git_dir;
> +       git_object_dir = git_path_from_env(DB_ENVIRONMENT, git_common_dir,
> +                                          "objects", &git_db_env);
> +       git_index_file = git_path_from_env(INDEX_ENVIRONMENT, git_dir,
> +                                          "index", &git_index_env);
> +       git_graft_file = git_path_from_env(GRAFT_ENVIRONMENT, git_dir,
> +                                          "info/grafts", &git_graft_env);

>         if (getenv(NO_REPLACE_OBJECTS_ENVIRONMENT))
>                 check_replace_refs = 0;
>         namespace = expand_namespace(getenv(GIT_NAMESPACE_ENVIRONMENT));
> diff --git a/path.c b/path.c
> index 3deb80c..8a6586c 100644
> --- a/path.c
> +++ b/path.c
> @@ -90,6 +90,38 @@ static void replace_dir(struct strbuf *buf, int len, const char *newdir)
>                 buf->buf[newlen] = '/';
>  }
>
> +static const char *common_list[] = {
> +       "/branches", "/hooks", "/info", "/logs", "/lost-found", "/modules",
> +       "/objects", "/refs", "/remotes", "/rr-cache", "/svn",
> +       "config", "gc.pid", "packed-refs", "shallow",
> +       NULL
> +};
> +
> +static void update_common_dir(struct strbuf *buf, int git_dir_len)
> +{
> +       char *base = buf->buf + git_dir_len;
> +       const char **p;
> +
> +       if (is_dir_file(base, "logs", "HEAD"))
> +               return; /* keep this in $GIT_DIR */
> +       for (p = common_list; *p; p++) {
> +               const char *path = *p;
> +               int is_dir = 0;
> +               if (*path == '/') {
> +                       path++;
> +                       is_dir = 1;
> +               }
> +               if (is_dir && dir_prefix(base, path)) {
> +                       replace_dir(buf, git_dir_len, get_git_common_dir());
> +                       return;
> +               }
> +               if (!is_dir && !strcmp(base, path)) {
> +                       replace_dir(buf, git_dir_len, get_git_common_dir());
> +                       return;
> +               }

> +       }
> +}
> +
>  static void adjust_git_path(struct strbuf *buf, int git_dir_len)
>  {
>         const char *base = buf->buf + git_dir_len;