From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Subject: Re: partially encrypted filesystem Date: Wed, 03 Dec 2003 20:25:09 -0500 Sender: linux-fsdevel-owner@vger.kernel.org Message-ID: <3FCE8CF5.4030006@pobox.com> References: <1070485676.4855.16.camel@nucleon> <20031203214443.GA23693@wohnheim.fh-wedel.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Cc: =?ISO-8859-1?Q?J=F6rn_Engel?= , linux-kernel@vger.kernel.org, "linux-fsdevel@vger.kernel.org" Return-path: Received: from parcelfarce.linux.theplanet.co.uk ([195.92.249.252]:37802 "EHLO www.linux.org.uk") by vger.kernel.org with ESMTP id S262925AbTLDBZ1 (ORCPT ); Wed, 3 Dec 2003 20:25:27 -0500 To: Linus Torvalds In-Reply-To: List-Id: linux-fsdevel.vger.kernel.org Linus Torvalds wrote: > With an encrypted filesystem, you can't do that. Or rather: you can do it > if the filesystem is read-only, but you definitely CANNOT do it on > writing. For writing you have to marshall the output buffer somewhere > else (and quite frankly, it tends to become a lot easier if you can do > that for reading too). > > And that in turn causes problems. You get all kinds of interesting > deadlock schenarios when write-out requires more memory in order to > succeed. So you need to get careful. Reading ends up being the much easier > case (doesn't have the same deadlock issues _and_ you could do it in-place > anyway). FWIW zisofs and ntfs have to do this too, since X on-disk compressed pages must be expanded to X+Y in-memory pages... Jeff