From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 07F68C677F1 for ; Sun, 15 Jan 2023 17:01:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231378AbjAORB3 (ORCPT ); Sun, 15 Jan 2023 12:01:29 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51054 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231356AbjAORB1 (ORCPT ); Sun, 15 Jan 2023 12:01:27 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D7501EC63; Sun, 15 Jan 2023 09:01:25 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 7DBB4B80B88; Sun, 15 Jan 2023 17:01:24 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0B724C433F0; Sun, 15 Jan 2023 17:01:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1673802083; bh=nm20lFRKKc6XWXsbu7enzGnNJtA20g3rsePVT32eB4E=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=arS7eNFYyrrPNVCfshIxQnCZlqWjtByG3mWM+t9r1SIRcZQNDQ+sAjlL5eDCJL38L umLKf3S0QodgIrV+acG2lo10aLFsw1WnhZnK0+6c+nf5yiciwPKXiPDDyhyiMi/9D9 W98Jr0WtFvJdFOeXPsx2m9zBnikOgWgBnQVmg0hhMsOBTnmowpwUzbRtCcU8CTnVmE OdY0x0ukh92zILzKOvx/gymehWetx9GZMUVpPkWckOGgv8RFLu9J/5LUod5gBvYFu1 vHttD/PpfDM88yyQz945s8MxxE1BQ6jOYLOsHjVE1j7lngK5BrjdeXNpQVdDQHF9/d BOeH4+nCXOAEw== Date: Sun, 15 Jan 2023 09:01:22 -0800 From: "Darrick J. Wong" To: Matthew Wilcox Cc: Christoph Hellwig , Andreas Gruenbacher , Dave Chinner , Alexander Viro , linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, cluster-devel@redhat.com, Christoph Hellwig Subject: Re: [RFC v6 04/10] iomap: Add iomap_get_folio helper Message-ID: References: <20230108213305.GO1971568@dread.disaster.area> <20230108194034.1444764-1-agruenba@redhat.com> <20230108194034.1444764-5-agruenba@redhat.com> <20230109124642.1663842-1-agruenba@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Tue, Jan 10, 2023 at 01:34:16PM +0000, Matthew Wilcox wrote: > On Tue, Jan 10, 2023 at 12:46:45AM -0800, Christoph Hellwig wrote: > > On Mon, Jan 09, 2023 at 01:46:42PM +0100, Andreas Gruenbacher wrote: > > > We can handle that by adding a new IOMAP_NOCREATE iterator flag and > > > checking for that in iomap_get_folio(). Your patch then turns into > > > the below. > > > > Exactly. And as I already pointed out in reply to Dave's original > > patch what we really should be doing is returning an ERR_PTR from > > __filemap_get_folio instead of reverse-engineering the expected > > error code. > > Ouch, we have a nasty problem. > > If somebody passes FGP_ENTRY, we can return a shadow entry. And the > encodings for shadow entries overlap with the encodings for ERR_PTR, > meaning that some shadow entries will look like errors. The way I > solved this in the XArray code is by shifting the error values by > two bits and encoding errors as XA_ERROR(-ENOMEM) (for example). > > I don't _object_ to introducing XA_ERROR() / xa_err() into the VFS, > but so far we haven't, and I'd like to make that decision intentionally. Sorry, I'm not following this at all -- where in buffered-io.c does anyone pass FGP_ENTRY? Andreas' code doesn't seem to introduce it either...? --D