From mboxrd@z Thu Jan 1 00:00:00 1970 From: Miklos Szeredi Subject: Re: [PATCH 00/32] VFS based Union Mount (V3) Date: Tue, 19 May 2009 12:35:01 +0200 Message-ID: References: <1242662968-11684-1-git-send-email-jblunck@suse.de> <20090519102939.GK16526@bolzano.suse.de> Cc: miklos@szeredi.hu, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk, bharata@in.ibm.com, dwmw2@infradead.org, mszeredi@suse.cz, vaurora@redhat.com To: jblunck@suse.de Return-path: Received: from fxip-0047f.externet.hu ([88.209.222.127]:50383 "EHLO pomaz-ex.szeredi.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751179AbZESKfL (ORCPT ); Tue, 19 May 2009 06:35:11 -0400 In-reply-to: <20090519102939.GK16526@bolzano.suse.de> (message from Jan Blunck on Tue, 19 May 2009 12:29:39 +0200) Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Tue, 19 May 2009, Jan Blunck wrote: > The directory in the topmost filesystem is created during > lookup. The contents of the directory isn't copied up presistently > at that point in time. Therefore you have an empty directory in the > topmost filesystem after the lookup. This was necessary to get rid > of the union_relookup_topmost() calls during create, mknod, mkdir > etc. > > When readdir is called, the topmost directory is filed up with > fallthru entries which are persistently stored. This is only > necessary to get readdir right wrt POSIX. During lookup the fallthru > dentry, which is in fact a special negative dentry, is ignored and > therefore the lookup continues on the lower filesystem. So this means that the topmost branch always needs to be writable, right? It isn't possible to make a union of two iso9660 filesystems, for example? Thanks, Miklos