From: Amir Goldstein Subject: Re: [LSF/FS TOPIC] Ext4 snapshots status update Date: Wed, 23 Mar 2011 22:19:38 +0200 Message-ID: References: <20110204002043.GA15658@noexit> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: lsf-pc@lists.linuxfoundation.org, linux-fsdevel , Ext4 Developers List , Theodore Tso , Chris Mason To: Joel Becker Return-path: Received: from mail-qy0-f181.google.com ([209.85.216.181]:35990 "EHLO mail-qy0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932896Ab1CWUTj convert rfc822-to-8bit (ORCPT ); Wed, 23 Mar 2011 16:19:39 -0400 In-Reply-To: <20110204002043.GA15658@noexit> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Fri, Feb 4, 2011 at 2:20 AM, Joel Becker wrote: > On Fri, Feb 04, 2011 at 12:33:39AM +0200, Amir Goldstein wrote: >> I have been working on porting Next3 snapshots to Ext4 >> with a group of 4 CS students. >> >> This is where it all happens: >> https://github.com/amir73il/ext4-snapshots >> >> Ext4 snapshots prototype is already working! >> Would you like to see a demo? >> >> I would like to present the progress of our work >> and discuss the remaining issues and how they should be best address= ed. >> >> Additionally, I would like to discuss the need for a unified snapsho= ts API that >> would serve both Ext4 and Btrfs. >> This could be useful for someone that wants to implement a generic >> snapshots management system. > > =A0 =A0 =A0 =A0ocfs2 definitely wants to be a part of that discussion= , as we > already do snapshots and thin clones. =A0ocfs2 snapshots are actually= just > thin clones marked readonly. =A0They can be placed anywhere in the > filesystem and are first-class inodes. =A0They do not live in a hidde= n > space like Next3 snapshots seem to. > =A0 =A0 =A0 =A0I've already got a design for a front-end snapshot pro= gram that > implements a policy on top this generic behavior. =A0This design woul= d > cover both first-class and hidden style snapshots, because it assume > snapshots are in a distinct namespace. =A0I haven't gotten around to > implementing it yet, but btrfs and other snapshottable filesystems we= re > part of the design goal. > > Joel > Hi Joel, Any chance of getting a copy of that design of yours, to get a head sta= rt for LSF? Here are some other generic snapshot related topics we may want to disc= uss: 1. Collaborating the use of inode flags COW_FL, NOCOW_FL, suggested by = Chris. 2. How to deal with mmap write to COW file, when you get ENOSPC. 3. Adding buffer_remap() flag for buffered I/O code, meaning, there is an existing mapping to initialize a page on partial write, but still ne= ed to call get_block() to get a (possibly) new mapping. I'll be staying for Collaboration summit, so I've got plenty of time if you like to exchange some ideas. Amir. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html