From: Jamie Lokier Subject: Re: [PATCH 13/35] fallthru: ext2 fallthru support Date: Mon, 19 Apr 2010 14:30:28 +0100 Message-ID: <20100419133028.GA3631@shareable.org> References: <1271372682-21225-8-git-send-email-vaurora@redhat.com> <1271372682-21225-9-git-send-email-vaurora@redhat.com> <1271372682-21225-10-git-send-email-vaurora@redhat.com> <1271372682-21225-11-git-send-email-vaurora@redhat.com> <1271372682-21225-12-git-send-email-vaurora@redhat.com> <1271372682-21225-13-git-send-email-vaurora@redhat.com> <1271372682-21225-14-git-send-email-vaurora@redhat.com> <20100419124025.GG10776@bolzano.suse.de> <1271682168.14748.718.camel@macbook.infradead.org> <20100419132344.GI10776@bolzano.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: David Woodhouse , Valerie Aurora , Alexander Viro , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Theodore Tso , linux-ext4@vger.kernel.org To: Jan Blunck Return-path: Received: from mail2.shareable.org ([80.68.89.115]:56950 "EHLO mail2.shareable.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754775Ab0DSNal (ORCPT ); Mon, 19 Apr 2010 09:30:41 -0400 Content-Disposition: inline In-Reply-To: <20100419132344.GI10776@bolzano.suse.de> Sender: linux-ext4-owner@vger.kernel.org List-ID: Jan Blunck wrote: > On Mon, Apr 19, David Woodhouse wrote: > > > On Mon, 2010-04-19 at 14:40 +0200, Jan Blunck wrote: > > > On Thu, Apr 15, Valerie Aurora wrote: > > > > > > > Add support for fallthru directory entries to ext2. > > > > > > > > XXX - Makes up inode number for fallthru entry > > > > XXX - Might be better implemented as special symlinks > > > > > > Better not. David Woodhouse actually convinced me of moving away from the > > > special symlink approach. The whiteouts have been implemented as special > > > symlinks before. > > > > I certainly asked whether you really need a real 'struct inode' for > > whiteouts, and suggested that they should be represented _purely_ as a > > dentry with type DT_WHT. > > > > I don't much like the manifestation of that in this patch though, > > especially with the made-up inode number. (ISTR I had other > > jffs2-specific objections too, which I'll dig out and forward). > > Yes, this patches still have issues that Val and me are aware off. I can't > remember anything jffs2-specific though. > > We return that inode number because we don't want to lookup the name on the > other filesystem during readdir. Therefore returning DT_UNKNOWN to let the > userspace decide if it needs to stat the file was the easiest workaround. I > know that POSIX requires d_ino and d_name but on the other hand it does not > require anything more on how long d_ino is valid. Although the lifetime of d_ino might very, I know some programs (not public) that will break if they see a d_ino which is wrongly matching the st_ino of another file somewhere on the same st_dev. They will assume the name is a hard link to the other file, without calling stat(), which I think is a reasonable assumption and a useful optimisation. So the made-up d_ino should at least be careful to not match an inode number of another file which has a stable st_ino. Why not zero for d_ino? -- Jamie