From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.cn.fujitsu.com ([183.91.158.132]:60678 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751690AbdK0JnA (ORCPT ); Mon, 27 Nov 2017 04:43:00 -0500 Received: from G08CNEXCHPEKD01.g08.fujitsu.local (unknown [10.167.33.80]) by cn.fujitsu.com (Postfix) with ESMTP id D64E9487F179 for ; Mon, 27 Nov 2017 17:42:52 +0800 (CST) Date: Mon, 27 Nov 2017 17:41:56 +0800 From: Lu Fengqi To: Subject: How about adding an ioctl to convert a directory to a subvolume? Message-ID: <20171127094156.GC29491@fnst.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Sender: linux-btrfs-owner@vger.kernel.org List-ID: Hi all, As we all know, under certain circumstances, it is more appropriate to create some subvolumes rather than keep everything in the same subvolume. As the condition of demand change, the user may need to convert a previous directory to a subvolume. For this reason，how about adding an ioctl to convert a directory to a subvolume? Users can convert by the scripts mentioned in this thread(https://www.spinics.net/lists/linux-btrfs/msg33252.html), but is it easier to use the off-the-shelf btrfs subcommand? After an initial consideration, our implementation is broadly divided into the following steps: 1. Freeze the filesystem or set the subvolume above the source directory to read-only; 2. Perform a pre-check, for example, check if a cross-device link creation during the conversion; 3. Perform conversion, such as creating a new subvolume and moving the contents of the source directory; 4. Thaw the filesystem or restore the subvolume writable property. In fact, I am not so sure whether this use of freeze is appropriate because the source directory the user needs to convert may be located at / or /home and this pre-check and conversion process may take a long time, which can lead to some shell and graphical application suspended. Please give your comments if any. -- Thanks, Lu