From: Jamie Lokier Subject: Re: [PATCH 1/4] vfs: vfs-level fiemap interface Date: Wed, 17 Sep 2008 16:02:12 +0100 Message-ID: <20080917150212.GD22613@shareable.org> References: <1221331767-16870-1-git-send-email-tytso@mit.edu> <20080914134711.GA21746@infradead.org> <20080914180132.GC13074@mit.edu> <20080914180843.GA31649@infradead.org> <20080914195811.GE13074@mit.edu> <20080915144754.GA16491@infradead.org> <20080916064514.GH3241@webber.adilger.int> <20080916220346.GB10562@mit.edu> <20080917141840.GB8750@logfs.org> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Theodore Tso , Andreas Dilger , Christoph Hellwig , linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, akpm@linuxfoundation.org, Mark Fasheh , mtk.manpages@gmail.com To: =?iso-8859-1?Q?J=F6rn?= Engel Return-path: Received: from mail2.shareable.org ([80.68.89.115]:49084 "EHLO mail2.shareable.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752352AbYIQPCY (ORCPT ); Wed, 17 Sep 2008 11:02:24 -0400 Content-Disposition: inline In-Reply-To: <20080917141840.GB8750@logfs.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: J=F6rn Engel wrote: > Apart from the typo above, here is a more discouraging version: >=20 > In general, accessing the block device directly is strongly discour= aged. > Exceptions exist mainly in the form of boot loaders like lilo and g= rub, > at a time when the filesystem is not (cannot be) mounted. >=20 > If the flag DATA_ENCODED is set, however, even this exception is no > longer valid. The content is encoded in some form. Details are > unknown, it could be compressed, encrypted or something else. I'm not clear about something from the above description. If I were writing a journalling / tree-like filesystem, and I did store data in blocks without encoding, but fsync() only waits for them to be committed to journal, not their final destination, and also they might be moved around - should I set DATA_ENCODED or not? (And should I return the temporary location in the long-running journal since that's the only place the data is committed at the time of the call?) Assume that even reading after unmounting is not 100% safe, because the data blocks could be relocated after calling FIEMAP (when the filesystem must be mounted), and before the unmount. -- Jamie -- 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