From: "Alexey Zaytsev" Subject: Re: Mentor for a GSoC application wanted (Online ext2/3 filesystem checker) Date: Mon, 21 Apr 2008 04:27:19 +0400 Message-ID: References: <20080419012952.GE25797@mit.edu> <20080419185603.GA30449@mit.edu> <480A42F6.2030005@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: "Theodore Tso" , linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, "Rik van Riel" To: "Eric Sandeen" Return-path: Received: from wa-out-1112.google.com ([209.85.146.179]:39703 "EHLO wa-out-1112.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753553AbYDUA1U (ORCPT ); Sun, 20 Apr 2008 20:27:20 -0400 Received: by wa-out-1112.google.com with SMTP id m16so2692934waf.23 for ; Sun, 20 Apr 2008 17:27:19 -0700 (PDT) In-Reply-To: <480A42F6.2030005@redhat.com> Content-Disposition: inline Sender: linux-ext4-owner@vger.kernel.org List-ID: On Sat, Apr 19, 2008 at 11:07 PM, Eric Sandeen wrote: > Theodore Tso wrote: > > On Sat, Apr 19, 2008 at 01:44:51PM +0400, Alexey Zaytsev wrote: > >> If it is a block containing a metadata object fsck has already read, > >> than we already know what kind of object it is (there must be a way > >> to quickly find all cached objects derived from a given block), and > >> can update the cached version. And if fsck has not yet read the > >> block, it can just be ignored, no matter what kind of data it > >> contains. If it contains metadata and fsck is intrested in it, it > >> will read it sooner or later anyway. If it contains file data, why > >> should fsck even care? > > It seems to me that what the proposed project really does, in essence, > is a read-only check of a filesystem snapshot. It's just that the > snapshot is proposed to be constructed in a complex and non-generic (and > maybe impossible) way. Maybe complex and non-generic, but also quite efficient. Only the actually used matadata is cached, and everything is done in userspace. > > If you really just want to verify a snapshot of the fs at a point in > time, surely there are simpler ways. If the device is on lvm, there's > already a script floating around to do it in automated fasion. (I'd > pondered the idea of introducing META_WRITE (to go with META_READ) and > maybe lvm could do a "metadata-only" snapshot to be lighter weight?) How do you tell data from metadata on this level? > > -Eric >