int submodule_move_head(const char *path,
			 const char *old,
			 const char *new,
			 unsigned flags)
{
	int ret = 0;
	struct child_process cp = CHILD_PROCESS_INIT;
	const struct submodule *sub;
	int *error_code_ptr, error_code;

	if (!is_submodule_active(the_repository, path))
		return 0;

	if (flags & SUBMODULE_MOVE_HEAD_FORCE)
		/*
		 * Pass non NULL pointer to is_submodule_populated_gently
		 * to prevent die()-ing. We'll use connect_work_tree_and_git_dir
		 * to fixup the submodule in the force case later.
		 */
		error_code_ptr = &error_code;
	else
		error_code_ptr = NULL;

	if (old && !is_submodule_populated_gently(path, error_code_ptr))
		return 0;

	sub = submodule_from_path(null_sha1, path);

	if (!sub)
		die("BUG: could not get submodule information for '%s'", path);

	if (old && !(flags & SUBMODULE_MOVE_HEAD_FORCE)) {
		/* Check if the submodule has a dirty index. */
		if (submodule_has_dirty_index(sub))
			return error(_("submodule '%s' has dirty index"), path);
	}

	if (!(flags & SUBMODULE_MOVE_HEAD_DRY_RUN)) {
		if (old) {
			if (!submodule_uses_gitfile(path))
				absorb_git_dir_into_superproject("", path,
					ABSORB_GITDIR_RECURSE_SUBMODULES);
		} else {
			char *gitdir = xstrfmt("%s/modules/%s",
				    get_git_common_dir(), sub->name);
			connect_work_tree_and_git_dir(path, gitdir);
			free(gitdir);

			/* make sure the index is clean as well */
			submodule_reset_index(path);
		}

		if (old && (flags & SUBMODULE_MOVE_HEAD_FORCE)) {
			char *gitdir = xstrfmt("%s/modules/%s",
				    get_git_common_dir(), sub->name);
			connect_work_tree_and_git_dir(path, gitdir);
			free(gitdir);
		}
	}

	prepare_submodule_repo_env(&cp.env_array);

	cp.git_cmd = 1;
	cp.no_stdin = 1;
	cp.dir = path;

	argv_array_pushf(&cp.args, "--super-prefix=%s%s/",
			get_super_prefix_or_empty(), path);
	argv_array_pushl(&cp.args, "read-tree", "--recurse-submodules", NULL);

	if (flags & SUBMODULE_MOVE_HEAD_DRY_RUN)
		argv_array_push(&cp.args, "-n");
	else
		argv_array_push(&cp.args, "-u");

	if (flags & SUBMODULE_MOVE_HEAD_FORCE)
		argv_array_push(&cp.args, "--reset");
	else
		argv_array_push(&cp.args, "-m");

	argv_array_push(&cp.args, old ? old : EMPTY_TREE_SHA1_HEX);
	argv_array_push(&cp.args, new ? new : EMPTY_TREE_SHA1_HEX);

	if (run_command(&cp)) {
		ret = -1;
		goto out;
	}

	if (!(flags & SUBMODULE_MOVE_HEAD_DRY_RUN)) {
		if (new) {
			child_process_init(&cp);
			/* also set the HEAD accordingly */
			cp.git_cmd = 1;
			cp.no_stdin = 1;
			cp.dir = path;

			prepare_submodule_repo_env(&cp.env_array);
			argv_array_pushl(&cp.args, "update-ref", "HEAD", new, NULL);

			if (run_command(&cp)) {
				ret = -1;
				goto out;
			}
		} else {
			struct strbuf sb = STRBUF_INIT;

			strbuf_addf(&sb, "%s/.git", path);
			unlink_or_warn(sb.buf);
			strbuf_release(&sb);

			if (is_empty_dir(path))
				rmdir_or_warn(path);
		}
	}
out:
	return ret;
}
int submodule_move_head(const char *path,
			 const char *old,
			 const char *new,
			 unsigned flags)
{
	int ret = 0;
	struct child_process cp = CHILD_PROCESS_INIT;
	const struct submodule *sub;
	int *error_code_ptr, error_code;

	if (!is_submodule_active(the_repository, path))
		return 0;

	if (flags & SUBMODULE_MOVE_HEAD_FORCE)
		 
		error_code_ptr = &error_code;
	else
		error_code_ptr = NULL;

	if (old && !is_submodule_populated_gently(path, error_code_ptr))
		return 0;

	sub = submodule_from_path(null_sha1, path);

	if (!sub)
		die("BUG: could not get submodule information for '%s'", path);

	if (old && !(flags & SUBMODULE_MOVE_HEAD_FORCE)) {
		 
		if (submodule_has_dirty_index(sub))
			return error(_("submodule '%s' has dirty index"), path);
	}

	if (!(flags & SUBMODULE_MOVE_HEAD_DRY_RUN)) {
		if (old) {
			if (!submodule_uses_gitfile(path))
				absorb_git_dir_into_superproject("", path,
					ABSORB_GITDIR_RECURSE_SUBMODULES);
		} else {
			char *gitdir = xstrfmt("%s/modules/%s",
				    get_git_common_dir(), sub->name);
			connect_work_tree_and_git_dir(path, gitdir);
			free(gitdir);

			 
			submodule_reset_index(path);
		}

		if (old && (flags & SUBMODULE_MOVE_HEAD_FORCE)) {
			char *gitdir = xstrfmt("%s/modules/%s",
				    get_git_common_dir(), sub->name);
			connect_work_tree_and_git_dir(path, gitdir);
			free(gitdir);
		}
	}

	prepare_submodule_repo_env(&cp.env_array);

	cp.git_cmd = 1;
	cp.no_stdin = 1;
	cp.dir = path;

	argv_array_pushf(&cp.args, "--super-prefix=%s%s/",
			get_super_prefix_or_empty(), path);
	argv_array_pushl(&cp.args, "read-tree", "--recurse-submodules", NULL);

	if (flags & SUBMODULE_MOVE_HEAD_DRY_RUN)
		argv_array_push(&cp.args, "-n");
	else
		argv_array_push(&cp.args, "-u");

	if (flags & SUBMODULE_MOVE_HEAD_FORCE)
		argv_array_push(&cp.args, "--reset");
	else
		argv_array_push(&cp.args, "-m");

	argv_array_push(&cp.args, old ? old : EMPTY_TREE_SHA1_HEX);
	argv_array_push(&cp.args, new ? new : EMPTY_TREE_SHA1_HEX);

	if (run_command(&cp)) {
		ret = -1;
		goto out;
	}

	if (!(flags & SUBMODULE_MOVE_HEAD_DRY_RUN)) {
		if (new) {
			child_process_init(&cp);
			 
			cp.git_cmd = 1;
			cp.no_stdin = 1;
			cp.dir = path;

			prepare_submodule_repo_env(&cp.env_array);
			argv_array_pushl(&cp.args, "update-ref", "HEAD", new, NULL);

			if (run_command(&cp)) {
				ret = -1;
				goto out;
			}
		} else {
			struct strbuf sb = STRBUF_INIT;

			strbuf_addf(&sb, "%s/.git", path);
			unlink_or_warn(sb.buf);
			strbuf_release(&sb);

			if (is_empty_dir(path))
				rmdir_or_warn(path);
		}
	}
out:
	return ret;
}